Diastereomeric Bis Research Articles

Dimerization and comments on the reactivity of homophthalic anhydride

Homophthalic anhydride (HPA) dimerizes under the influence of base to provide, sequentially, the (3–4′)-C-acyl dimer, a pair of chiral diastereomeric bis(lactones), 3-(2-carboxybenzyl)isocoumarin-4-carboxylic acid, and finally, 3-(2-carboxybenzyl)isocoumarin. The structures of the bis(lactones) were misassigned in 1970 based on the (presumed) cis thermal decarboxylative elimination reaction of the lower melting one. The preferred pathway should be trans–anti, however, and crystallographic analysis of one of the bis(lactones) reverses the earlier assignment. The formal cycloaddition reaction of HPA with imines occurs in preference to HPA dimerization; the mechanistic implications of this reactivity difference are discussed.

Photochemical reactions of tetrachloro-1,4-benzoquinone (chloranil) with tricyclo[4.1.0.02,7]heptane (Moore's hydrocarbon) and bicyclo[4.1.0]hept-2-ene (2-norcarene)

Solutions of chloranil (CA) in benzene were irradiated in the presence of Moore's hydrocarbon (MH) and 2-norcarene (NC). These reactions brought about four common products, namely 2,3,5,6-tetrachlorohydroquinone (TCH) and three 1 : 1 cycloadducts, whose C7H10 subunits were reorganised in comparison to the skeletons of MH and NC. As the fifth product, a norcar-3-en-2-yl ether of TCH was formed in the case of NC, whereas MH gave rise to a substance having the structure of the diastereomeric bis(endo-2-norcaryl) ethers of TCH. A control experiment demonstrated that this substance is also produced from MH and TCH without irradiation. In view of the known addition of acids onto MH to give norcaranes substituted in position 2 and the known acid-catalysed isomerisation of MH to NC, it seems obvious that TCH was the only genuine product of the photoreaction of CA with MH. Being an acid, TCH then not only took up two equivalents of MH furnishing the bisethers referred to but also catalysed the rearrangement of MH to NC, which served as a substrate for excited CA to yield the three 1 : 1 cycloadducts mentioned.

Multifunctional and Reactive Enantiopure Organometallic Helicenes: Tuning Chiroptical Properties by Structural Variations of Mono‐ and Bis(platinahelicene)s

Acetylacetonato-platina[6]- and -platina[7]helicenes have been prepared from 2-pyridyl-substituted benzophenanthrene ligands by following a two-step cycloplatination reaction. The photophysical properties (UV-visible absorption and emission behavior) and chiroptical properties (circular dichroism and molar rotation) of the resolved enantiomers have been measured. These metallahelicenes constitute a novel family of easily accessible helicene derivatives that exhibit large and tuneable chiroptical properties that can be rationalized theoretically and compared to the parent [6]- and [7]carbohelicenes. Furthermore, they are red phosphors at room temperature and their large chiroptical properties can be modulated by oxidation of the metal center to Pt(IV). Hetero- and homochiral diastereomeric bis(metallahelicene)s that possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands have also been prepared. It is shown that the heterochiral (P,M)-bis(Pt(III)-[6]helicene) 9a(1) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene) 9a(2). Spectral assignments and an analysis of the optical rotation of these systems were made with the help of time-dependent density functional theory. The calculations highlight the contributions of the metal centers to the chiroptical properties. For 9a(1) and 9a(2), σ-π conjugation between the helicenes and the Pt-Pt moiety may contribute strongly to the optical rotation and electronic circular dichroism.

From Hetero- to Homochiral Bis(metallahelicene)s Based on a PtIII−PtIII Bonded Scaffold: Isomerization, Structure, and Chiroptical Properties

Hetero- and homochiral diastereomeric bis(metallahelicene)s have been synthesized. They possess a rare Pt(III)-Pt(III) scaffold bridged by benzoato ligands. It is shown that heterochiral (P,M)-bis(Pt(III)-[6]helicene) can isomerize into the homochiral (P,P)- and (M,M)-bis(Pt(III)-[6]helicene). A theoretical study shows a unique σ-π conjugation between the two π-helices and the σ-Pt(III)-Pt(III) scaffold that impacts the strong chiroptical properties.

Bis(hydroxy-isoindolinone)s: Synthesis, Stereochemistry, Polymer Chemistry, and Supramolecular Assembly

Pseudoacid chlorides of 2,5-bis(4-fluorobenzoyl) terephthalic acid and 4,6-bis(4-fluorobenzoyl) isophthalic acid condense with primary amines to afford diastereomeric bis(hydroxyindolinone)s in good isolated yields and with diamines to give high molecular weight poly(hydroxyindolinone)s. Bis-N-pyrenemethyl bis(hydroxyindolinone)s assemble, even in dipolar solvents such as DMSO, with macrocyclic diimide-sulfones to give [3]pseudorotaxanes stabilized by electronically complementary aromatic pi-pi-stacking and shape-complementary van der Waals interactions.

Stereodivergent synthesis of the first bis(cyclobutane) γ-dipeptides and mixed γ-oligomers

Diastereomeric bis(cyclobutane) γ-dipeptides, a new class of γ-peptides, have been synthesized efficiently from both enantiomers of conveniently protected 3-amino-2,2-dimethyl-1-carboxylic acid. These amino acids have been prepared in very good overall yields through enantiodivergent synthetic routes starting from (−)- cis-pinononic acid. Mixed γ-oligomers have also been prepared from GABA and cyclobutane residues.

New Enantiopure Bis(thioether) and Bis(sulfoxide) Ligands from Benzothiophene

AbstractThe C2‐symmetric compound 2,3,2,3‐tetrahydro‐2,2‐bi(benzo[b]thiophenyl) and three diastereomeric bis(oxide) derivatives can be synthesized in a few steps from benzo[b]‐thiophene by oxidative homocoupling of (R)‐2,3‐dihydro‐benzo[b]thiophene 1‐oxide. This new family of enantiopure bis(thioether) and bis(sulfoxide) ligands forms stable chelating PdII complexes. The fused pentacyclic structure of the complexes imparts a rigid chiral environment around the metal centre. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Stereodivergent syntheses of the first bis(cyclobutane) β-dipeptides

The efficient synthesis of methyl 2-benzyloxycarbonylamino-(1 S,2 R)-cyclobutane-1-carboxylate starting from 2-methoxycarbonyl-(1 R,2 S)-cyclobutane-1-carboxylic acid is described. This β-amino acid derivative is antipodal with respect to the (1 R,2 S)-compound that was previously synthesized in our laboratory from the same chiral hemi ester. In turn, these enantiomeric β-amino acids have been self-condensed and coupled with one another to provide, respectively, enantiomeric and diastereomeric bis(cyclobutane) β-dipeptides. These products are the first reported β-amino acid oligomers containing two directly linked cyclobutane residues.

Synthesis and Absolute Configuration of Novel Mono- and Dinuclear Cobalt(III) Complexes Containing S-Phenylalanine

Two diastereomers of bis(1,3-diaminopropane)(S-phenylalaninato)cobalt(III) were prepared by reaction of S-phenylalanine with carbonatobis(1,3-diaminopropane)cobalt(III). The diastereomers were separated on an optically active Sephadex QAE column and their absolute configurations assigned by means of circular dichroism. In addition, 1HNMR spectra of the diastereomers were analyzed in terms of the population of the three predominant rotamers of the coordinated S-phenylalaninato ligand. One out of 24 theoretically possible diastereomers of the dinuclear species di- µ -hydroxo- tetrakis(S-phenylalaninato)dicobalt(III) was obtained by direct synthesis and its absolute configuration deduced from CD spectra.

Bis(phospholane) Ligands Containing Chiral Backbones. Matching and Mismatching Effects in Enantioselective Hydrogenation of α-Keto Esters

The preparation of a series of new bis(phospholane) ligands is described. A convenient procedure that allows the synthesis of secondary 2,5-dialkylphospholanes and their borane adducts has been developed. Use of the borane adducts to prepare diastereomeric bis(phospholane) ligands possessing chiral 2,4-pentane backbones also is described. Stereochemical matching and mismatching effects within these ligands are assessed in rhodium-catalyzed asymmetric hydrogenation reactions. In the hydrogenation of α-keto esters, substantially higher enantioselectivities (up to 78% ee) are observed with catalysts derived from the matched ligand relative to the analogous mismatched ligand and the ligand possessing an achiral 1,3-propane backbone. Two diastereomeric rhodium catalyst precursors have been characterized by X-ray crystallography, and the results have been analyzed in an effort to correlate the hydrogenation data with specific structural features of the catalysts.

Synthesis of four diastereomeric 3,5-dialkoxy-2,4-dimethylalkanals by a simple extension of the non-aldol aldol process to bis(propionates).

[formula: see text] The synthesis of all four diastereomers of bis(propionates), 3,5-dialkoxy-2,4-dimethylalkanals, by non-aldol aldol chemistry is described. The epoxy alcohols (3, 4) were converted into the mesylates (9, 11) which were cleanly rearranged to the desired 3,5-bis(oxygenated)-2,4-dimethylalkanals (10, 12) in high yield. The epoxy mesylates (13, 16) gave the desired products (14, 17) in good yield on treatment with TMSOTf and a hindered base.

Propylene Polymerization with Chiral and Achiral Unbridged 2-Arylindene Metallocenes

Unbridged 2-arylindenyl metallocene complexes, such as bis(2-phenylindenyl)zirconium dichloride, in the presence of methyaluminoxane (MAO) are catalyst precursors for the synthesis of elastomeric polypropylenes. The effects of 1-methyl substitution on the polymerization behavior of these unbridged 2-arylindene complexes have been studied. The reaction of the lithium salt of 1-methyl-2-phenylindene with ZrCl4 leads to the formation of two diastereomers of bis(1-methyl-2-phenylindenyl)zirconium dichloride: rac- and meso-(1-Me-2-PhInd)2ZrCl2. The two isomers have been separated by fractional crystallization and identified by X-ray crystallography. X-ray crystallographic analysis reveals that the dihedral angles between the planes of the phenyl and the indenyl rings have significantly increased upon 1-methyl substitution (28−34° compared to 10−12° for unsubstituted (2-PhInd)2ZrCl2), which suggests strong steric repulsion between the 1-methyl and 2-phenyl groups. In ethylene polymerization, the productivity o...

Assignment of Absolute Configuration to Metabolically Formedtrans-Dihydrodiols of Dibenzo[a,l]pyrene by the Exciton Chirality Method Using a New Red-Shifted Chromophore

Abstract Absolute configuration was assigned to the enantiomers of the metabolically formed trans-11,12-dihydrodiol of dibenzo[a,l]pyrene by application of a CD spectroscopic method. For this purpose (±)-trans-11,12-dihydrodiol was converted to its diastereomeric bis(menthoxyacetates) followed by preparative separation of the diastereomers on silica gel. Hydrolysis of the two diastereomers gave the (+)- and (−)-11,12-dihydrodiols. To achieve assignment of the absolute configuration by the nonempirical exciton chirality method both the (+)- and (−)-dihydrodiol were transformed to their bis-4[4′-(dimethylamino)phenylazo]benzoates. The CD spectra of the bis-4[4′-(dimethylamino)phenylazo]benzoates revealed that (R,R)-configuration is associated with the (−)-11,12-dihydrodiol, whereas the (+)-11,12-dihydrodiol possesses (S,S)-configuration. Based on this assignment the absolute structures of the stereoselectively synthesized enantiomeric fjord-region 11,12-dihydrodiol 13,14-epoxides being potential ultimate ca...

ChemInform Abstract: Reaction of Diastereomeric Bis(cyclohexyl)‐2,2′‐diones with Hydrogen Peroxide. Structure of the Resulting Adducts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

2,6‐Dicyano‐1,5‐dimethyl‐4,8‐diphenylsemibullvalene. — Synthesis, Structure and the Reactions with Triplet Oxygen

AbstractAddition of trimethylsilyl cyanide to the diphenylbicyclo[3.3.0]octanedione 8c is catalyzed by the potassium cyanide/18‐crown‐6 complex and produces a mixture of the diastereomeric bis[O‐(trimethylsilyl)cyanohydrins] endo‐ and exo‐10c (3:2). The hydrogen fluoride—pyridine complex in phosphorus oxychloride as solvent and, subsequently, an excess of pyridine convert the mixture of diastereomers 10c into the unsaturated y,y′‐diphenyldinitrile 11. This is converted into the red semibullvalene 4 in a single step by treatment with hexachloroethane and concentrated aqueous sodium hydroxide in the presence of tetrabutylammonium hydroxide as phase‐transfer catalyst — Above 30°C, 4 isomerizes in solution to a mixture of the cyclooctatetraenes 12 and 13. While the red crystals of 4 are stable in the atmosphere, in the dark affording the endoperoxide 16 and the yellow 2H‐pyran derivative 17 (7:1) which result from parallel reactions. Only at temperatures as high s 110°C, 16 slowly rearranges to 17 which reacts further to yield well‐defined but still unknown products. The simultaneous formation of 16 and 17 at low temperatures is interpreted in terms of endo and exo attack, respectively, of triplet oxygen at the benzylic carbon atoms of the semibullvalene 4 or the isomeric bicyclic diradical 21. — The structures of the new compounds are based on spectroscopic evidence and X‐ray diffraction analyses of 4, endo‐10c, 11, 16, and 17. The semibullvalene 4 exists as a pair of rapidly rearranging degenerate valence tautomers in solution and in the crystal as well. In the solid state, 4 exhibits apparent C2 symmetry and equal atomic distances C2–C8 and C4–C6 (201.9 pm). Because true degeneracy is highly unlikely in the crystal, the equal distribution of two non‐equivalent valence tautomers at room termperature results from a fortuitous cancelling of the ΔH° and TΔS° terms governing the equilibrium. — The red colour of 4 in the crystal and in solution is due to a maximum at 444 nm which disappears on cooling. Thus, 4 not only belongs to the family of thermochromic semibullvalenes and barbaralanes devoid of a long wavelength chromophor like 1, 6 and 14, but also shows the most intensive maximum at the longest wavelength observed so far.

2,6‐Dicyan‐4,8‐diphenylbarbaralan

2,6‐Dicyano‐4,8‐diphenylbarbaralane[1]Conjugate addition of the phenylcuprate reagent, obtained from phenyllithium, copper(I) cyanide, and boron trifluoride–diethylether, to the bicyclo[3.3.1]nonadienedione 3 affords the diphenylbicyclo[3.3.1]nonanedione 4 in high yield. Catalyzed by the potassium cyanide/18‐crown‐6 complex, addition of trimethylsilyl cyanide produces a mixture of the diastereomeric bis[O‐(trimethylsilyl)cyanohydrins] exo,exo‐, exo,endo‐ and endo,endo‐5. The hydrogen fluoride – pyridine complex in phosphorus oxychloride as solvent and, subsequently, an excess of pyridine convert the diastereomers 5 into the unsaturated γ,γ′1‐diphenyldinirile 6. This is brominated by N1‐bromosuccinimide to yield the γ,γ′1‐dibromodinitriles exo‐ and endo‐ 7 (6:1). The predominant diastereomer exo‐7 is debrominated by the zinc‐copper couple to afford the orange‐red title compound 2 in 78% yield. More conveniently, the unsaturated dinitrile 6 is converted to 2 in a single step by treatment with hexachloroethane and concentrated aqueous sodium hydroxide in the presence of tetrabutylammonium hydroxide as phase‐transfer catalyst. Surprisingly, low yields of 2 are also obtained when the bis[O‐(trimethylsilyl)cyanohydrins] 5 or the unsaturated dinitrile 6 are treated with phosphorus oxychloride in boiling pyridine. – The structures of the new compounds are based on spectroscopic evidence and X‐ray diffraction analyses of 2, 4, and endo,endo‐5. The conformations of 4 and endo,endo‐5 in solution are inferred on the basis of vicinal proton coupling constants and a comparison with coupling constants calculated with the aid of the Karplus equation and torsional angles obtained by X‐ray diffraction analyses. – While the barbaralane 2 exists as a pair of very rapidly rearranging degenerate valence tautomers in solution, the degeneracy is lifted in the crystal lattice. As a result, the crystal consists of two rapidly rearranging but non‐equivalent valence tautomers in a ratio of 9:1 as estimated from the apparent atomic distance C2–C8 of 2 and the C2–C8 bond length of non‐rearranging barbaralanes. – The colour of 2 in the crystal and in solution results from a maximum at 436 nm which increases on heating of the solution to 450 K. Cooling to 77 K results in reversible fading and the disappearance of the maximum. Thus, 2 is a barbaralane like 1 which exhibits colour though it is lacking a classical long‐wavelength chromophore.

NMR INVESTIGATIONS ON DIASTEREOMERIC MIXTURES OF BIS(DIALKOXYTHIOPHOSPHORYL) SULFANES AND -POLYSULFANES CONTAININGsec. BUTOXY GROUPS. ASSIGNMENT OF31P,13C AND1H NMR SIGNALS IN A MIXTURE OF SEVEN DIASTEREOMERS USING SHIFT-CORRELATED 2D NMR SPECTRA

Abstract Synthesizing compounds of the structure diastereomeric mixtures were obtained. If possible, the 31P chemical shifts and P[sbnd]P coupling constants of the individual diastereomers were determined from the 31P NMR spectra of these diastereomeric mixtures. In addition, the mixture of the seven diastereomers of bis(di-sec. butoxythiophosphoryl)disulfane was analyzed using shift-correlated 31P[sbnd]31P {1H}, 13C-31P {1H}, 13C-1H {31P} and 1H-1H {31P) 2D NMR spectra. In this way, the 31P, 13C and 1H chemical shifts and the corresponding coupling constants were assigned to the diastereomers. The appearance of regions of similar chemical shift into which the 1H, 13C and 31P signals of identical atoms or atom groups can be classified is characteristic of all the diastereomeric mixtures investigated. These regions can be explained mainly by the symmetry relations of a molecule moiety (sBuO)2P(S)S[sbnd].

ChemInform Abstract: Synthesis of Optically Active Fjord‐Region 11,12‐Diol 13,14‐Epoxides and the K‐Region 9,10‐Oxide of the Carcinogen Benzo(g)chrysene.

Optically pure enantiomers of the diastereomeric pair of benzo(g)chrysene-11,12-diol 13,14-epoxides (Scheme VI) were synthesized from (11R,12R)- and (11S,12S)-dihydroxy-11,12-dihydrobenzo(g)chrysenes (16(R,R) and 16(S,S)). Two routes were employed to synthesize the racemic dihydrodiol 16. Although the Prevost method for introduction of the trans-vicinal oxygen atoms at C{sub 11} and C{sub 12} of 13,14-dihydrobenzo(g)chrysene (7) proceeded poorly, introduction of the trans-vicinal oxygen atoms was readily achieved by hydration of the tetrahydro 11,12-epoxide (9, Scheme II) or by NaBH{sub 4} reduction of benzo(g)chrysene-11,12-dione (17, Scheme IV). The latter method is the most effective for the synthesis of the racemic dihydrodiol 16, whereas the former method is preferred for the preparation of substantial amounts of the enantiomers of 16 since the diastereomeric bis-(-)-menthyloxy esters of the tetrahydrodiol 11 (Scheme V) are much more effectively separated by HPLC than are the corresponding derivatives of the dihydrodiol 16. The conformational preference of the hydroxyl groups in the series-1 diol epoxide in which the benzylic 11-hydroxyl group and the epoxide oxygen are cis (19, Figure 2) was found to be dependent upon solvent, with a quasidiequatorial conformation being preferred in DMSO-d{sub 6} and a quasidiaxial conformation being preferred in CDCl{sub 3}. As anticipated from prior studies of the ratesmore » of hydrolysis of the 3,4-diol 1,2-epoxides of benzo(c)phenanthrene, the present 11,12-diol 13,14-epoxides are relatively stable in neutral, aqueous media. Enantiomers of the K-region 9,10-oxide 24 were prepared from benzo(g)chrysene (Scheme IX).« less

Synthesis of optically active fjord-region 11,12-diol 13,14-epoxides and the K-region 9,10-oxide of the carcinogen benzo[g]chrysene

Optically pure enantiomers of the diastereomeric pair of benzo(g)chrysene-11,12-diol 13,14-epoxides (Scheme VI) were synthesized from (11R,12R)- and (11S,12S)-dihydroxy-11,12-dihydrobenzo(g)chrysenes (16(R,R) and 16(S,S)). Two routes were employed to synthesize the racemic dihydrodiol 16. Although the Prevost method for introduction of the trans-vicinal oxygen atoms at C{sub 11} and C{sub 12} of 13,14-dihydrobenzo(g)chrysene (7) proceeded poorly, introduction of the trans-vicinal oxygen atoms was readily achieved by hydration of the tetrahydro 11,12-epoxide (9, Scheme II) or by NaBH{sub 4} reduction of benzo(g)chrysene-11,12-dione (17, Scheme IV). The latter method is the most effective for the synthesis of the racemic dihydrodiol 16, whereas the former method is preferred for the preparation of substantial amounts of the enantiomers of 16 since the diastereomeric bis-(-)-menthyloxy esters of the tetrahydrodiol 11 (Scheme V) are much more effectively separated by HPLC than are the corresponding derivatives of the dihydrodiol 16. The conformational preference of the hydroxyl groups in the series-1 diol epoxide in which the benzylic 11-hydroxyl group and the epoxide oxygen are cis (19, Figure 2) was found to be dependent upon solvent, with a quasidiequatorial conformation being preferred in DMSO-d{sub 6} and a quasidiaxial conformation being preferred in CDCl{sub 3}. As anticipated from prior studies of the ratesmore » of hydrolysis of the 3,4-diol 1,2-epoxides of benzo(c)phenanthrene, the present 11,12-diol 13,14-epoxides are relatively stable in neutral, aqueous media. Enantiomers of the K-region 9,10-oxide 24 were prepared from benzo(g)chrysene (Scheme IX).« less

Bis(α,β-ditrifloxystyryl)mercury: Synthesis and crystal structure

Abstract Reaction of bis(α-diazophenacyl)mercury or its p -methyl derivative with triflic anhydride [(CF 3 SO 2 ) 2 O] leads to three diastereomeric bis(α,β-ditrifloxystyryl)mercury compounds. For ( E , E )-bis(α,β-ditrifloxystyryl)mercury, an X-ray structural determination was carried out. The reaction represents another example of attack of the anhydride on the oxygen atom of an α-diazocarbonyl compound.