Isopropyl Derivatives Research Articles

Effect of α-Substitution on the Reactivity of C(sp3)-H Bonds in Pd0-Catalyzed C-H Arylation.

We report mechanistic studies on the reactivity of different α-substituted C(sp3)-H bonds, -CHnR (R = H, Me, CO2Me, CONMe2, OMe, and Ph, as well as the cyclopropyl and isopropyl derivatives -CH(CH2)2 and -CHMe2) in the context of Pd0-catalyzed C(sp3)-H arylation. Primary kinetic isotope effects, kH/kD, were determined experimentally for R = H (3.2) and Me (3.5), and these, along with the determination of reaction orders and computational studies, indicate rate-limiting C-H activation for all substituents except when R = CO2Me. This last result was confirmed experimentally (kH/kD ∼ 1). A reactivity scale for C(sp3)-H activation was then determined: CH2CO2Me > CH(CH2)2 ≥ CH2CONMe2 > CH3 ≫ CH2Ph > CH2Me > CH2OMe ≫ CHMe2. C-H activation involves AMLA/CMD transition states featuring intramolecular O → H-C H-bonding assisted by C-H → Pd agostic bonding. The "AMLA coefficient", χ, is introduced to quantify the energies associated with these interactions via natural bond orbital 2nd order perturbation theory analysis. Higher barriers correlate with lower χ values, which in turn signal a greater agostic interaction in the transition state. We believe that this reactivity scale and the underlying factors that determine this will be of use for future studies in transition-metal-catalyzed C(sp3)-H activation proceeding via the AMLA/CMD mechanism.

Aqueous Polyelectrolyte Electrodeposition: The Effects of Alkyl Substitution and Varying Supporting Electrolyte Concentrations on the Deposition Efficiency

AbstractThe controlled growth of surface‐modifying polymer films by electrodeposition often fails because of the lack of redox activity of these compounds. Here, electroactive complexants help to electrodeposit non‐electroactive polymers. Hence, we investigate the counterion‐induced electrodeposition of polyelectrolytes: three quaternized poly(N,N‐dialkylaminoethyl methacrylate)s (qPDAAEMA), in particular their methyl, ethyl, and isopropyl derivatives (i. e. qPDMAEMA, qPDEAEMA, and qPDPAEMA), provide transparent solutions in the presence of hexacyanoferrate(II) (ferrocyanide) at specific concentration windows of the KCl supporting electrolyte. Below a certain KCl concentration, insolubility dominates irrespective of the hexacyanoferrate valency, whilst above an upper threshold, full solubility is observed. Between these limits, oxidation reversibly electrodeposits polymer/hexacyanoferrate(III) (ferricyanide) complexes. Hydrodynamic voltammetry (and data analysis using in‐house software) provides access to the deposition efficiency (DE). qPDEAEMA with ethyl substituents shows highest DEs; larger or smaller substituents fall short because of a balance between “hydrophobicity” and charge separation, shifting the window toward smaller salt concentrations with increasing alkyl size. We always observe a DE maximum close to the minimum salt concentration, whilst electrochemical quartz crystal microbalance (EQCM) measurements indicate a change in film water content close to the maximum. These effects, being also discussed in terms of polymer conformation, can direct the future engineering of electroassisted coatings.

Structural and Spectroscopic Studies of Steric and Electronic Substituent Effects in a Series of Magnesium Aminodiboranates Mg[(BH3)2NMeR]2.

The magnesium N,N-dimethylaminodiboranate compound Mg[(BH3)2NMe2]2, the most volatile compound of magnesium known, serves as an excellent chemical vapor deposition (CVD) precursor for the growth of thin films such as the dielectric material MgO. To explore how the thermal stability and physical properties of magnesium aminodiboranates depend on the steric and electronic properties of the nitrogen-bound substituents, we have made a series of analogues of Mg[(BH3)2NMe2]2, in which one of the two methyl substituents on nitrogen is replaced with an ethyl, iso-propyl, or tert-butyl group. In the crystal structure of Mg[(BH3)2NMe(t-Bu)]2, the magnesium center is coordinated to two chelating (BH3)2NMe(t-Bu) ligands, each of which binds in a κ2,κ2 fashion so that the magnesium center forms eight Mg-H contacts. Unlike Mg[(BH3)2NMe2]2, however, which has a linear N···Mg···N angle and is an isolated molecule in the solid state, the N···Mg···N angle in Mg[(BH3)2NMe(t-Bu)]2 is distinctly nonlinear (149.9°) because hydrogen atoms of BH3 groups of nearby molecules form two additional Mg-H contacts with the magnesium center. When the complexes are heated in toluene solution, the (BH3)2NMeR- groups reversibly undergo B-N bond cleavage (with concomitant migration of a hydrogen atom) to release the aminoborane BH2═NMeR and form magnesium borohydride, Mg(BH4)2. For the methyl, ethyl, and iso-propyl derivatives, the equilibrium strongly favors Mg[(BH3)2NMeR]2. In contrast, for the tert-butyl derivative, the equilibrium strongly favors BH2═NMe(t-Bu) and Mg(BH4)2. The results suggest that more strongly electron-donating groups slightly strengthen the B-N bonds and disfavor B-N bond cleavage, provided that the groups are not too large. In contrast, sterically bulky ligands disfavor B-N bond reformation, thus promoting the dissociative equilibrium that involves B-N bond cleavage. Interestingly, the rates at which the complexes approach equilibrium depend only weakly on the nature of the R group, at least within the series studied. These findings are relevant to the potential use of magnesium aminodiboranates as CVD precursors to the superconducting phase MgB2.

Analytical Separation of Closantel Enantiomers by HPLC.

Closantel is an antiparasitic drug marketed in a racemic form with one chiral center. It is meaningful to develop a method for separating and analyzing the closantel enantiomers. In this work, two enantiomeric separation methods of closantel were explored by normal-phase high-performance liquid chromatography. The influences of the chiral stationary phase (CSP) structure, the mobile phase composition, the nature and proportion of different mobile phase modifiers (alcohols and acids), and the column temperature on the enantiomeric separation of closantel were investigated in detail. The two enantiomers were successfully separated on the novel CSP of isopropyl derivatives of cyclofructan 6 and n-hexane-isopropanol-trifluoroacetic acid (97:3:0.1, v/v/v) as a mobile phase with a resolution (Rs) of about 2.48. The enantiomers were also well separated on the CSP of tris-carbamates of amylose with a higher Rs (about 3.79) when a mixture of n-hexane-isopropanol-trifluoroacetic acid (55:45:0.1, v/v/v) was used as mobile phase. Thus, the proposed separation methods can facilitate molecular pharmacological and biological research on closantel and its enantiomers.

Strong intramolecular hydrogen bonds and steric effects involving C═S groups: An NMR and computational study.

A number of 5-acyl rhodanines and thiorhodanines with bulky acyl groups (pivaloyl and adamantoyl), not previously available, have been synthesized. The compounds are shown to exist in the enol form. Structures have been calculated using both the MP2 approach and the B3LYP-GD3BJ functional and the 6-311++G(d,p) basis set. Hydrogen bond energies are estimated by subtracting energies of a structure with the OH group turned 180° from those of the intramolecularly hydrogen-bonded one. Properties such as OH chemical shifts, two-bond isotope effects on 13 C chemical shifts, electron densities at the bond critical point from atoms in molecules analysis, and the hydrogen bond energies show that the sterically hindered compounds have stronger hydrogen bonds than methyl or isopropyl derivatives. The combination of oxygen and sulfur derivatives enables a detailed analysis of hydrogen bond energies.

Investigations on the thermoresponsive behavior of copoly(2-oxazoline)s in water

Polymers with a lower critical point solution temperature (LCST) are widely investigated responsive materials and are already in use for smart materials applications, e.g., for medicinal purposes. Hydrogels prepared from these polymers usually exhibit a shrinking behavior over a broad temperature range, rather than an expected sharp phase transition. One reason for this is their cloud point temperature (Tcp) dependence on the concentration in water. Here, we investigate this behavior on the example of copolymers prepared by copolymerization of 2-ethyl-2-oxazoline (EtOx) with the respective heptyl (HepOx), butyl (BuOx), and isopropyl (iPrOx) derivatives, respectively. The resulting copolymers show greatly different dependencies of their TCP on concentration. While P(EtOx-stat-HepOx)s show a strong linear increase of Tcp on polymer concentration, the Tcp of P(EtOx-stat-BuOx)s is only slightly raising at higher concentration. P(EtOx-stat-iPrOx)s have two plateau regions in their water/polymer phase diagram. In general, copolymers with less strong differences in their hydrophobicity might be best suited for discretely thermo-switchable hydrogels, because they show the lowest dependence of Tcp on polymer concentration.

Fast photorefractive response in polymeric composites enabled by the control of chromophore free volume.

The molecular orientation of a chromophore importantly affects the electro-optic characteristics of polymeric photorefractive composites. We designed methyl, ethyl, and isopropyl derivatives of 4-piperidinobenzylidene-malononitrile (PDCST) with the aim of enhancing molecular orientation properties, and investigated the effects of alkyl substitution on the electro-optic properties and response times of polymeric photorefractive composites. The three alkyl-substituted PDCSTs showed enhanced electro-optic responses and photorefractive grating buildup rates.

Structure‐Activity Analysis of Bisphenol‐Z Derivatives for Anticancer Activity

Much of the research surrounding bisphenol derivatives focuses on their use as polymers and plasticizers for industry. Research has demonstrated that bisphenol‐A (BPA) adversely affects humans via endocrine disruption through hormonal modulation. Despite the recent explosion in BPA research, little effort has been devoted to researching the biological activities of other bisphenol derivatives, including bisphenol‐Z (BPZ). Initial screening of BPZ revealed moderate in vitro anticancer activity against four diverse human cancer cell lines (A375 malignant melanoma, A‐172 glioblastoma, HT‐29 colorectal adenocarcinoma, and MCF7 breast adenocarcinoma) with IC50 values of approximately 65 μM following 24 hour treatments. In an attempt to enhance the activity of BPZ, seven analogs with varying degrees of polarity, lipophilicity, and sterics on the cyclohexane ring were synthesized. Screening of these analogs revealed that polar substitutions resulted in a loss of activity, while a simple methyl substitution had similar activity to BPZ. Anticancer activity was enhanced relative to BPZ following substitution with an ethyl, isopropyl, or N‐palmitoyl group at the 4‐ position. The most active compounds from this structure‐activity study were the N‐palmitoyl (LS4) and isopropyl (LS6) derivatives with 24 hour IC50 values ranging from 25 to 53 μM and 33 to 42 μM respectively.Given the increased activity of LS4 and LS6, additional studies were performed including a trypan blue exclusion assay and a Caspase‐Glo® 3/7 assay. The results of these studies revealed exclusion of trypan blue at supra‐IC50 concentrations six hours after treatments, suggestive of a non‐necrotic mechanism of death. To determine if caspase‐dependent apoptosis was involved, we performed a Caspase‐Glo® 3/7 assay. Functional screening of executioner caspase‐3 and ‐7 revealed significant increases in activity following a 12 hour treatment with LS4 in all cells lines. This effect was least evident in the MCF7 cells, potentially due to a mutation wherein these cells lack expression of caspase‐3. In contrast, LS6 failed to activate executioner caspases‐3 and ‐7 in these same cell lines.In conclusion, this structure‐activity study revealed that nonpolar substitution at the 4‐ position of BPZ enhanced anticancer activity. Additionally, membrane integrity remained intact following exposure to LS4 and LS6. While LS4 activated executioner caspases‐3/7, LS6 failed to activate this hallmark pathway of apoptotic death. Further investigations are ongoing to elucidate the mechanisms of cell death, identify putative cellular targets, and determine potential selectivity against normal human cell lines.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Synthesis, Structural Characterization, and H2 Evolution Study of a Spheroid‐Shape Hydride‐Rich Copper Nanocluster

AbstractThis study reports on new bis‐2‐butyl dithiophosphate‐stabilized polyhydrido copper nanoclusters, [Cu32(H)20{S2P(O2Bu)2}12], 1H, and [Cu20H11{S2P(O2Bu)2}9], 2H. The clusters 1H and 2H have been characterized by a variety of techniques including multinuclear NMR (1H, 2H, 31P), electrospray ionization mass spectrometry (ESI‐MS), and low temperature X‐ray crystallography. The presence of hydride ligands was supported by the 2H NMR spectrum of the deuteride analogs [Cu32(D)20{S2P(O2Bu)2)12], 1D and [Cu20D11{S2P(O2Bu)2}9], 2D. The metal skeleton of 1H revealed that a hexacapped rhombohedron of fourteen copper atoms was sandwiched between two sets of eighteen (9x2) copper atoms in a cup shape and the entire cluster is an elongated triangular gyrobicupola. The metal core is stabilized by 20 hydride ligands via various (μ3, μ4, μ5)‐H coordination modes and 12 dithiophosphate ligands coordinated either in tetrametallic tetraconnective (η4: μ2, μ2) or trimetallic tetraconnective (η3: μ2, μ2) patterns. The structural motif of 2H showed fascinating correlations with 1H having an elongated triangular orthobicupola framework of eighteen (9x2) copper atoms with an encapsulated linear Cu2 unit along the C3 axis and protected by 11 (μ3, μ4)‐H and 9 dithiophosphate ligands in a tetrametallic tetraconnective (η4: μ2, μ2) mode. The isopropyl derivatives, [Cu32(H)20{S2P(OiPr)2}12], 3H and [Cu20(H)11{S2P(OiPr)2}9], 4H, were used to study H2 evolution under different physico‐chemical conditions and proved to be excellent models for hydrogen storage materials. Additionally, following H2 evolution under sunlight irradiation, mild thermolysis (∼60 oC) and acidification, cluster 3H converted into [Cu8(H){S2P(OiPr)2}6]+, 5H. Intriguingly 5H can react with Cu+ salt in the presence of [BH4]− and re‐form 3H. Cluster 4H also reproducibly re‐formed via the reaction between 5H and [BH4]− from which a continuous cycle of cluster conversion and H2 evolution is proposed. Rhombus‐shaped copper nanoparticles fabricated from further reductions of 3H and 4H showed the intermediary role of metal hydrides in the formation of metal nanoparticles under wet chemical methods.

Crystal structures of three sterically congested disilanes.

In the three sterically congested silanes, C24H38Si2 (1) (1,1,2,2-tetra-isopropyl-1,2-di-phenyl-disilane), C24H34Br4Si2 (2) [1,1,2,2-tetra-kis-(2-bromo-propan-2-yl)-1,2-di-phenyl-disilane] and C32H38Si2 (3) (1,2-di-tert-butyl-1,1,2,2-tetra-phenyl-disilane), the Si-Si bond length is shortest in (1) and longest in (2), with (3) having an inter-mediate value, which parallels the increasing steric congestion. A comparison of the two isopropyl derivatives, (1 and 2), shows a significant increase in the Si-C(ipso) distance with the introduction of bromine. Also, in the brominated compound 2, attractive inter-molecular Br⋯Br inter-actions exist with Br⋯Br separations ca 0.52 Å shorter than the sum of the van der Waals radii. In compound 2, one of the bromo-isopropyl groups is rotationally disordered in an 0.8812 (9):0.1188 (9) ratio. Compound 3 exhibits 'whole mol-ecule' disorder in a 0.9645 (7):0.0355 (7) ratio with the Si-Si bonds in the two components making an angle of ca 66°.

The empirical comparison of cyclofructans and cyclodextrins as chiral selectors in capillary electrophoretic separation of atropisomers of R,S-1,1'-binaphthalene-2,2'-diyl hydrogen phosphate.

Native cyclofructans and their isopropyl derivatives were studied as chiral selectors in capillary electrophoresis and compared with α- and β-cyclodextrin. R,S-1,1'-Binaphthalene-2,2'-diyl hydrogen phosphate was used as a model chiral compound. The empirical observation of the enantioselectivity of native cyclofructans and isopropyl derivatives of cyclofructans was described and compared with the cyclodextrins. The influence of methanol and acetonitrile, as the most commonly used organic solvents, and sodium dodecyl sulfate as a micelle forming additive on the separation of R,S-1,1'-binaphthalene-2,2'-diyl hydrogen phosphate atropisomers was achieved. The different enantiorecognition abilities resulting from unlike interaction mechanism with R,S-1,1'-binaphthalene-2,2'-diyl hydrogen phosphate were observed for the studied cyclodextrins and cyclofructans, especially when methanol or sodium dodecyl sulfate were used as modifiers of the separation conditions.

Chiral Ag(i) and Pt(ii) complexes of ditopic NHC ligands: synthesis, structural and spectroscopic properties

The butyl and isopropyl derivatives (4I, 5Br) of chiral pool derived bis-imidazolium dehydrohexitol salts have been prepared. The ditopic N-heterocyclic carbenes 4 and 5 form dinuclear Ag(I) and Pt(II) complexes. All compounds were fully characterised by multinuclear NMR spectroscopy. The bis-imidazolium salt 4I and platinum complexes cis-[Pt(2)(μ-2)(dmso)(2)Cl(4)] and cis-[Pt(2)(μ-4)(dmso)(2)Cl(4)] were characterised by X-ray crystallography. In the case of the Pt(II) complexes, the carbene ring is positioned in a sterically preferred orientation, approximately perpendicular to the platinum coordination plane. The (1)H, (13)C, (15)N and (195)Pt NMR spectra of the platinum complexes show the presence of rotamers due to hindered rotation about the carbene-metal bond.

A detailed thermodynamic profile of cyclopentyl and isopropyl derivatives binding to CK2 kinase

The detailed understanding of the molecular features of a ligand binding to a target protein, facilitates the successful design of potent and selective inhibitors. We present a case study of ATP-competitive kinase inhibitors that include a pyradine moiety. These compounds have similar chemical structure, except for distinct terminal hydrophobic cyclopentyl or isopropyl groups, and block kinase activity of casein kinase 2 subunit α (CK2α), which is a target for several diseases, such as cancer and glomerulonephritis. Although these compounds display similar inhibitory potency against CK2α, the crystal structures reveal that the cyclopentyl derivative gains more favorable interactions compared with the isopropyl derivative, because of the additional ethylene moiety. The structural observations and biological data are consistent with the thermodynamic profiles of these inhibitors in binding to CK2α, revealing that the enthalpic advantage of the cyclopentyl derivative is accompanied with a lower entropic loss. Computational analyses indicated that the relative enthalpic gain of the cyclopentyl derivative arises from an enhancement of a wide range of van der Waals interactions from the whole complex. Conversely, the relative entropy loss of the cyclopentyl derivative arises from a decrease in the molecular fluctuation and higher conformational restriction in the active site of CK2α. These structural insights, in combination with thermodynamic and computational observations, should be helpful in developing potent and selective CK2α inhibitors.

Cyclopropyl and Isopropyl Derivatives of 11-cis and 9-cis Retinals at C-9 and C-13: Subtle Steric Differences with Major Effects on Ligand Efficacy in Rhodopsin

Retinal is the natural ligand (chromophore) of the vertebrate rod visual pigment. It occurs in either the 11-cis (rhodopsin) or the 9-cis (isorhodopsin) configuration. In its evolution to a G protein coupled photoreceptor, rhodopsin has acquired exceptional photochemical properties. Illumination isomerizes the chromophore to the all-trans isomer, which acts as a full agonist. This process is extremely efficient, and there is abundant evidence that the C-9 and C-13 methyl groups of retinal play a pivotal role in this process. To examine the steric limits of the C-9 and C-13 methyl binding pocket of the binding site, we have prepared C-9 and C-13 cyclopropyl and isopropyl derivatives of its native ligands and of α-retinal at C-9. Most isopropyl analogues show very poor binding, except for 9-cis-13-isopropylretinal. Most cyclopropyl derivatives exhibit intermediate binding activity, except for 9-cis-13-cyclopropylretinal, which presents good binding activity. In general, the binding site shows preference for the 9-cis analogues over the 11-cis analogues. In fact, 13-isopropyl-9-cis-retinal acts as a superagonist after illumination. Another surprising finding was that 9-cyclopropylisorhodopsin is more like native rhodopsin with respect to spectral and photochemical properties, whereas 9-cyclopropylrhodopsin behaves more like native isorhodopsin in these aspects.

Comparison of photoenolization and alcohol release from alkyl-substituted benzoyl benzoic esters

Photolysis of 1B in argon-saturated solutions yields 4B and releases methanol. Laser flash photolysis of 1B shows formation of biradical 2B, which has a lifetime of ~50 ns and a λmax at 330 nm. Biradical 2B undergoes an intersystem crossing to form photoenols E-3B and Z-3B with a λmax at 390 nm. Laser flash photolysis shows that the lifetimes of E-3B and Z-3B are affected by the solvent. Density functional theory calculations demonstrate that the transition-state barrier for a 1,5-H atom shift from Z-3B to regenerate 1B is affected by the ortho-alkyl substituents, whereas the stereoelectronics of the alkyl substituent affect the transition-state barrier of E-3B as it undergoes electrocyclic ring closure to form 4B. The photoreactivity of 1B was compared with its analogous methyl and isopropyl derivatives 1A and 1C, respectively, to better estimate the effect of the alkyl substituent on reactivity.

Experimental and Theoretical Investigations of the Contact Ion Pairs Formed by Reactions of the Anions [(EPR2)2N]− (R = iPr, tBu; E = S, Se) with the Cations [(TePR2)2N]+ (R = iPr, tBu)

Reactions of the sodium salts [(EPR(2))(2)N]Na(TMEDA) (R = (i)Pr, (t)Bu; E = S, Se) with the iodide salts [(TePR(2))(2)N]I (R = (i)Pr, (t)Bu) in toluene produce the mixed-chalcogen systems [(EPR(2))(2)N][(TePR(2))(2)N] (6b, E = Se, R = (t)Bu; 6c, E = S, R = (t)Bu; 7b, E = Se, R = (i)Pr; 7c, E = S, R = (i)Pr). Compounds 6b, 6c, 7b, and 7c have been characterized in solution by variable-temperature multinuclear ((31)P, (77)Se, and (125)Te) NMR spectroscopy and in the solid state by single-crystal X-ray crystallography. The structures are comprised of contact ion pairs linked by bonds between Te and S or Se atoms. For the tert-butyl derivatives 6b and 6c, the anionic half of the molecule is coordinated in a bidentate (E,E') fashion to one Te atom of the cationic half to give a spirocycle, whereas in the isopropyl derivatives 7b and 7c, the anion acts as a monodentate ligand with only one E-Te bond and the second S or Se atom pointing away from the cation. A comparison of the chalcogen-chalcogen bond orders in 6b, 6c, and the all-tellurium system 6a (E = Te), as determined from the experimental bond lengths, shows that the Te-Te bond order in the cations decreases as the strength of the E-Te interaction increases. This trend is attributed to increased electron donation from the anion into the lowest unoccupied molecular orbital [sigma*(Te-Te)] of the cation along the series S < Se < Te. A similar trend is observed for the monodentate contact ion pairs 7b and 7c. Density functional theory calculations provided information about the relative energies of bidentate and monodentate contact ion pair structures and the extent of intramolecular electron transfer in these systems.

Homolytic alkylation of some 3,4‐quinolinediyl bis‐sulfides under minisci reaction conditions

Abstractmagnified imageReaction of hydrogen sulfate of 3,4‐quinolinediyl bis‐sulfides 1a, 2a, 3a, and 4a with isopropyl and cyclohexyl radicals formed from alkyl iodide/hydrogen peroxide/DMSO/Fe++ salt system took place at α‐quinolinyl position and led to the respective mono‐ and dialkyl derivatives 1b‐e, 2b‐e, 3b,c, and 4b,c. Action of sodium methoxide towards isopropyl derivatives 1b,c and 2b,c caused the 1,4‐dithiin ring opening to form (after S‐methylation) derivatives of 3,4′‐ and 3,3′‐diquinolinyl sulfides 6a,b and 7a,b.

Hydrogermolysis reactions involving the α-germylated nitriles R 3GeCH 2CN (R = Ph, Pr i, Bu t) and germanium amides R 3GeNMe 2 (R = Pr i, Bu t) with Ph 3GeH: Substituent-dependent reactivity and crystal structures of Pr i3GeGePh 3 and Bu t3Ge[NHC(CH 3)CHCN

The α-germylated nitriles R 3GeCH 2CN (R = Ph, Pr i , Bu t ) and germanium amides R 3GeNMe 2 (R = Pr i and Bu t ) have been prepared and characterized and their reactivity with Ph 3GeH in CH 3CN has been explored to investigate their utility for the construction of Ge–Ge bonds. In each case the phenyl and iso-propyl derivatives furnish the corresponding digermanes R 3GeGePh 3 (R = Ph, Pr i ) where the amide reagents are converted to R 3GeCH 2CN in situ which subsequently react with Ph 3GeH. The rate of the Ge–C bond cleavage reactions was found to depend on the steric and electronic properties of the organic substituents. Attempted synthesis of Bu t 3GeGePh 3 by these methods did not result in the desired product but rather in isolation of the 3-amidocrotononitrile species Bu t 3Ge[NHC(CH 3)CHCN]. The crystal structures of Pr i 3GeGePh 3 and Bu t 3Ge[NHC(CH 3)CHCN] have been determined.

Polymorphism in Fuchsones

Seven 2,6-disubstituted fuchsones (fuchsone = 4-(α,α-diphenylmethylene)-1,4-benzoquinone, R = H, Me, i-Pr, t-Bu, Ph, Cl, Br) were synthesized and crystallized from different solvents to find new polymorphs in this family of compounds. The chloro and isopropyl derivatives are dimorphic, methyl, and t-butyl compounds crystallized as trimorphs, but H-, Ph-, and Br-substituted compounds gave one crystal structure each. Polymorphism in a family of compounds is discussed for the first time with respect to different conformations adopted by the exodiphenylmethylene group at the 4-position of the benzoquinone ring. Depending on the acceptor availability of the fuchsone C═O and the conformation of the phenyl ring, different C−H···O interactions, and close packing motifs are optimized in these crystal structures. One polymorph of dichloro-fuchsone has Z′ = 4 due to offset in the stacking of symmetry-independent molecules. Phase transition in dimethyl fuchsone showed the β polymorph to be stable at high temperature, whereas the α form dominates at room temperature, making it an enantiotropic cluster. The three experimental polymorphs of dimethyl fuchsone lie within the 10 lowest-energy predicted crystal structures. Fuchsones represent easy to synthesize compounds derived via a molecular engineering approach for the study of conformational polymorphism.

Bicyclo[2.2.2]octane analogues of patchouli alcohol by Sakurai reaction and Nagata cyclization. Synthesis and olfactory properties of novel isopropyl derivatives

The synthesis of bicyclo(2.2.2)octane patchouli alcohol analogues by the Sakurai conjugate addition and Nagata cyclization is described. By this approach, complementary to those so far adopted and based on the Diels-Alder addition, known analogues 2, 3 and 20 and new analogues 8-11, with 1-isopropylbicyclo(2.2.2)octane structure, could be obtained. The olfactory properties of 8 and 10 were also evaluated.