Martin Ligand Research Articles

Aziridine Formation with Retention of Configuration from a Pentacoordinated 1,2-Thiazetidine Bearing Two Chiral Centers at the 3- and 4-Positions

Abstract Tetracoordinated and pentacoordinated 1,2-thiazetidines bearing the Martin ligand, trans-5 and trans-6, were synthesized as stable compounds. The X-ray crystallographic analyses showed that trans-5 and trans-6 have distorted pseudotrigonal bipyramidal (pseudo-TBP) and TBP structures, respectively, and that the two phenyl groups at the 3- and 4-positions of both compounds are cis to each other. Thermal isomerization of the aziridine cis-11, which is considered a thermolysis product of trans-6, occurred even at relatively low temperature (100 °C) in solution and made it difficult to determine the stereochemistry of the aziridine formation from trans-6 in solution. Flash vacuum pyrolysis, which potentially prevents the isomerization of the product, was applied to trans-6 to give eventually the stereochemistry-retained aziridine cis-11. This result indicates a ligand coupling pathway in the aziridine formation process from trans-6.

Synthesis, Structure, and Thermolysis of Tetracoordinated 1λ4,2‐Selenazetidines Bearing Two Chiral Centers at the 3‐ and 4‐Positions

ABSTRACTThe title trans and cis isomers (trans‐3 and cis‐3) were successfully synthesized as stable compounds by taking advantage of the Martin ligand. The X‐ray crystallographic analysis of trans‐3 showed that it has a distorted pseudotrigonal bipyramidal structure, and that the two phenyl groups at the 3‐ and 4‐positions are cis to each other. The thermolysis of trans‐3 in the presence of excess dimethyl acetylenedicarboxylate (DMAD) gave a mixture of the corresponding aziridines (trans‐7 and cis‐7) and cycloadducts (11a and 11b) of the azomethine ylides formed by ring opening of the aziridines with DMAD. Heating of cis‐7 and excess DMAD under the same conditions gave diastereomeric mixtures of both the aziridines and the cycloadducts, which means that the stereochemistry of the aziridine formation from the 1,2‐selenazetidine cannot be determined in this system.

Chemistry of Four-Membered Ring Compounds Containing a Hypervalent Sulfur Atom and a Heteroatom at the Neighbor Positions

Title compounds containing tetracoordinated and pentacoordinated sulfur together with oxygen, nitrogen, or sulfur were successfully synthesized as stable compounds. They contain the Martin ligand, which is well known to be able to stabilize such highly coordinated main group compounds. X-ray crystallographic analyses revealed that they have distorted trigonal bipyramidal (TBP) or pseudo-TBP structures. In marked contrast to group 13–15 element analogues, which afford the corresponding alkenes upon heating, thermolyses of compounds bearing an oxygen or nitrogen atom gave the corresponding oxiranes or aziridine, suggesting the possibility that these compounds are intermediates of the Corey-Chaykovsky reaction of sulfur ylides with carbonyl compounds or imines. Thermolysis of 1λ4,2-dithietanes also gave the corresponding thiiranes. The stereochemistry (retention of configuration) of formation of these three-membered ring compounds is also described.

Efficient synthesis of tetradecafluoro-4-phenylheptan-4-ol by a Cannizzaro-type reaction and application of the alcohol as a bulky Martin ligand variant for a new anti-apicophilic phosphorane

Alcohols 8 bearing two identical perfluoroalkyl groups were prepared by the reaction of the corresponding perfluoroalkyl phenyl ketones 7 with 0.5 equivalents of t-BuOK via Cannizzaro-type disproportionation. Utilizing the new bulky bidentate ligand with two n-C(3)F(7) groups generated from 8c, anti-apicophilic phosphorane 5a and its stable isomer 6a were synthesized. The crystal structures of 5a and 6a were slightly affected by the steric repulsion of heptafluoropropyl groups. Kinetic studies on the isomerization of 5a to 6a showed that the new ligand was effective for decreasing the isomerization rate compared with its C(2)F(5) analog 3a to about half.

Solution and Crystal Structure of a Hexacoordinate Phosphoranate Bearing Two Martin Ligands and Two Methyl Groups

A hexacoordinate phosphoranate bearing two Martin ligands and two methyl groups was synthesized by the reaction of the monocyclic phosphorane bearing a hydroxy group with KH, and was crystallized in the presence of 18-crown-6 ether. The crystal structure of the phosphoranate could be regarded as an intermediate model in the reaction of the O-equatorial methylphosphorane with a methyl anion.

Dynamic aspects of hypervalent compounds effected by the formation of three center‐four electron bond in heteroatoms

AbstractHypervalent bond (three center‐four electron bond: 3c‐4e) is the central feature of the structure and reactivity of hypervalent compounds. The SSS bond of thiathiophthene, the so‐called no‐bond resonance compound, is realized as one of the examples of 3c‐4e bond centered at the sulfur atom (10‐S‐3). A variety of reactions such as cycloaddition‐elimination, bond‐switching rearrangement, and bond‐switching equilibration of sulfur‐containing heterocycles are exemplified to proceed through the presence of hypervalent 10‐S‐3 species. In the transition state of edge inversion, it is predicted that a vacant p‐type orbital is perpendicular to the square planar species. Antimony(III) and bismuth(III) compounds bearing a bidentate Martin ligand and a phenyl, or 2‐dimethylaminomethylphenyl, or 2,6‐bis(dimethylaminomethyl)phenyl group were prepared. The rates of inversion of these compounds at the central atom of Sb or Bi were accelerated significantly by the coordination of the dimethylamino group and also of pyridine from the solvent, where 3c‐4e bond is formed by the coordination to stabilize the transition state. Finally, the presence of rapid bond‐switching equilibration between NB···N bond of 1,8‐bis(dimethylamino)‐9‐(substituted)borylanthracenes was shown to proceed through 10‐B‐5 species at the transition state. It is concluded that the bond‐switching equilibration takes place as a piston rod in the range of 1.32 Å. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:161–175, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20326

Synthesis and Application of a Bidentate Ligand Based on Decafluoro‐3‐phenyl‐3‐pentanol: Steric Effect of Pentafluoroethyl Groups on the Stereomutation of O‐Equatorial C‐Apical Spirophosphoranes

1,1,1,2,2,4,4,5,5,5-Decafluoro-3-phenyl-3-pentanol was prepared by a Cannizzaro-type disproportionation reaction, and the dimetallated compound was used as a bidentate ligand, which is bulkier than the Martin ligand (1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol). A P-H spirophosphorane was synthesized by utilizing the new bidentate ligand, and the structure of the product was essentially the same as that of the P-H phosphorane with Martin ligands. Phosphoranes that exhibit reversed apicophilicity (O-equatorial) were also synthesized and could be converted into the corresponding stable stereoisomers (O-apical). The crystal structures of O-equatorial phosphoranes and the O-apical isomers were slightly affected by the steric repulsion of pentafluoroethyl groups. Kinetic measurements revealed that the stereomutation of O-equatorial methylphosphorane to the O-apical isomer was slowed. The activation enthalpy for the stereomutation of the former to the latter was higher than that of the phosphorane with Martin ligands by 5.1 kcal mol(-1).

A New Method for the Formation of Anti‐apicophilic (O‐cis) Spirophosphoranes – Kinetic Studies on the Stereomutation of O‐cis Arylspirophosphoranes to Their O‐trans Isomers

AbstractP–H spirophosphorane 4 bearing two Martin ligands was converted to dianions (5a–n), bearing R groups, with excess organolithium reagents (RLi). Subsequent oxidation with I2 at ambient temperature gave anti‐apicophilic (O‐cis) spirophosphoranes 2a–n. All anti‐apicophilic phosphoranes 2a–n isomerized irreversibly to the O‐trans spirophosphoranes 3a–n, respectively. For 2,6‐dialkylphenyl derivatives 2k–n, the barrier for pseudorotation between enantiomers 2‐RP and 2‐Sp was rather high, and thus the interconversion could not be observed on the NMR timescale. The activation parameters for the pseudorotation of the triisopropylphenyl (TIP) derivative 2n to 3n were almost identical with those of nBu derivative 2b to 3b, i.e., ΔH‡ = 21.3 kcal mol–1, ΔS‡ = –9.4 eu. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The Ligand‐Exchange Process of P–Hapical Phosphoranes and the Thermal Formation and Pseudorotation of Anti‐Apicophilic Spirophosphoranes

AbstractMonocyclic P–Hapical phosphoranes 10 bearing a ring‐opened Martin ligand are formed upon treatment of the P–Hequatorial spirophosphorane 7 with more than 2 equiv. of alkyllithium compounds. A ligand‐exchange process of these phosphoranes 10 involving the interconversion of the bidentate Martin ligand with the monodentate Martin ligand was found to proceed, probably through a hexacoordinate phosphorus atom. Heating of 10 in nondonating solvents furnished alkylspirophosphoranes 5, whereas heating of 10 in donor solvents led to the formation of anti‐apicophilic phosphoranes 6, a new class of phosphoranes in which the less apicophilic carbon substituent occupies an apical position and the more apicophilic oxygen atom occupies an equatorial position. These phosphoranes 6 were found to completely convert into their energetically more stable Cequatorial,Oapical stereoisomers 5 upon heating. On the basis of kinetic examinations of the cyclization process of 10, the formation of 6 can be rationalized by the enhanced nucleophilicity of the hydroxy group in the donor solvents. The isomer 5b was estimated to be more stable than 6b (R = nBu) by 12 kcal mol–1 from kinetic studies on the pseudorotation of 6b to 5b. This is in good agreement with theoretical calculations with analogous 5a and 6a (R = Me), which estimate the difference in energy to be 14.1 kcal mol–1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

New Aspects in the Chemistry of Three‐membered Ring Compounds Containing a Highly Coordinate Main Group Element

Abstract The title compounds were synthesized by taking advantage of the Martin ligand. Their structures were determined by X‐ray crystallography. Pentacoordinate thiasiliranides were hydrolyzed to give the corresponding thiol. Pentacoordinate chalcogenaphosphiranes were found to have polar P‐chalcogen bonds, which were confirmed by their reactions with CF 3SO3Me to give the corresponding 1‐(methylchalcogena)alkylphosphonium triflates and by the solvent‐dependent NMR studies.

Synthesis and Reactions of β-Oxophosphoranes / Ylides Containing a Cyclic or Acyclic P-Moiety

β-Oxophosphoranes / ylides, versatile intermediates in synthetic organic chemistry can be prepared by the novel reaction of P-aryl cyclic phosphine oxides, such as 2,3-dihydro- and 2,3,4,5-tetrahydro-1H-phosphole 1- oxides, as well as 1,2-dihydrophosphinine 1-oxides with dialkyl acetylenedicarboxylates (DAAD). The reaction involves a spirocyclic oxaphosphete intermediate formed by the (2+2) cycloaddition of the P=O bond and the acetylene moiety and follows an inverse Wittig protocol that was evaluated by PM3 and Hartree-Fock ab initio quantum chemical calculations. The interaction of iminophosphine derivatives of the Martin ligand with acetylenic diacid esters follows a similar reaction path affording β-iminophosphoranes / ylides. In these cases, the azaphosphete is an intermediate, or one component of an equilibrium system. Another synthetic method for β- oxophosphoranes / ylides comprises the acylation of stabilised phosphonium ylides in position α. Under flash vacuum pyrolytic conditions, the b-oxophosphoranes / ylides are fragmented to the mixture of the corresponding acetylene and phosphine oxide. This reaction path is exactly the opposite of the formation of b-oxophosphoranes from a phosphine oxide and acetylene derivative that was mentioned above. Some other reactions of heterocyclic b- oxophosphoranes / ylides, such as reduction, deacylation and alkoholysis are also discussed that lead to valuable families of compound. Keywords: oxophosphoranes/Ylides, acyclic p-moiety, p-aryl cyclic phosphine oxides, dialkyl acetylenedicarboxylates, spirocyclic oxaphosphete, hartree-fock ab initio quantum

Synthesis, Structure, and Thermolysis of a Pentacoordinate 1,2-Oxastibetane

Isomeric pentacoordinate 1,2-oxastibetanes bearing the Martin ligand have been synthesized by the reactions of bromo(2-hydroxyalkyl)stiboranes with sodium hydride of which one of the isomers was characterized by X-ray crystallographic analysis and NMR spectroscopy. Thermolysis of the isomer shown (CD3CN, 140 degrees C) afforded the oxirane with retention of configuration, while its thermolyses in the presence of lithium bromide and LiBPh4.3DME provided the oxirane with inversion of configuration and the olefin. The addition of the salts in the thermolyses of this pentacoordinate 1,2-oxastibetane controls both the stereochemistry of the oxirane formed and the ratios of the three main products.

Syntheses, Structures, and Thermolyses of Three‐ and Four‐Membered Heterocyclic Compounds Containing Highly Coordinate Main Group Elements

AbstractFor Abstract see ChemInform Abstract in Full Text.

Syntheses, Structures, and Thermolyses of Three- and Four-Membered Heterocyclic Compounds Containing Highly Coordinate Main Group Elements

Abstract Most titled compounds were synthesized by taking advantage of the Martin ligand. Their structures were determined by X-ray crystallography. Thermolyses of most of the four-membered ring compounds gave the corresponding Wittig-type products, while those of 1,2-oxasiletanides in the presence of proton source afforded the homo-Brook rearrangement products depending on bulkiness of the substituent at the 3-position. Pentacoordinate thiasiliranides were hydrolyzed to give the corresponding thiol, which seems to be formed via the initial cleavage of the Si–C bond followed by further hydrolysis of the corresponding thia-Brook rearrangement product. On the other hand, the most polarized bond of a pentacoordinate selenaphosphirane was found to be the P–Se bond, which was confirmed by its reaction with CF3SO3Me to give the corresponding 1-(methylseleno)alkylphosphonium triflate and by the solvent-dependent NMR study.

Stereospecific stilbene formation from β-hydroxy-α,β-diphenylethylphosphoranes. Mechanistic proposals based upon stereochemistry

Abstract All four diastereomers of β-hydroxy-α,β-diphenylethylspirophosphoranes bearing two Martin ligands were prepared from a P–H (equatorial) spirophosphorane. Treatment of these phosphoranes with t-BuOK or t-BuONa at low temperature (ca. −40°C) led to the formation of stilbene with complete stereospecificity. In half of the cases the reaction proceeded quantitatively, whereas the other half gave rise to retro-aldol reaction with the formation of varying amounts of benzaldehyde and benzylphosphorane. A kinetic examination revealed that of the four the quantitatively proceeding reaction that gives cis-stilbene was the fastest. Based on the experimental observations, a mechanistic rationale for the previously reported Wittig-type reaction of exceptionally high Z-selectivity using an ethoxycarbonylmethylspirophosphorane is presented.

Synthesis and structure of the first 1,2sigma5-selenaphosphirane.

A 1,2sigma5-selenaphosphirane bearing the Martin ligand was synthesized. Its structure in both the solid and the solution state was established by X-ray crystallographic analysis and NMR measurements, respectively. The selenaphosphirane has a polar P-Se bond, and the selenium atom is negatively charged. In the solution state, the degree of polarization of the P-Se bond depends on the acceptor number of the solvents.

Cocrystallization of Two Different Pseudorotamers of Monocyclic Phosphorane Bearing Two Martin Ligands

Solution and crystal structures of monocyclic pentacoordinate phosphoranes bearing two Martin ligands and two carbon substituents are described. When the two carbon substituents are different, relative apicophilicity of the two monodentate carbon substituents could be determined based on the equilibrium ratio of the pseudorotamers. In some cases, x-ray structural analysis could be carried out and the crystallized structure from CH 3 CN is consistent with the major pseudorotamer in solution (CD 3 CN). Furthermore, when the equilibrium ratio of pseudorotamers is almost unity, novel cocrystallization of two pseudorotamers in a single crystal was observed.

Synthesis of Four- and Five-Membered Heterocycles Derived from an Iminophosphorane

Reactions of an iminophosphorane bearing the Martin ligand with a ketone, an isothiocyanate, and an alkyne gave the corresponding cycloadducts, 1,3,2 u 5 -oxazaphosphetidine, 1,3,2 u 5 -diazaphosphetidine-4-thione, and 1,2 u 5 -azaphosphetine, respectively, while that with dimethyl acetylenedicarboxylate (DMAD) and successive hydrolysis afforded the 1,2 u 5 -oxaphosphole-(2 H )-one. Thermal reactions of the cycloadducts were also studied.

Fluoride Ion Abstraction of Phosphonium Cations from Their Counter Anion: A Novel Synthetic Method of Fluorophosphoranes

Abstract The phosphonium cations bearing the Martin ligand abstracted a fluoride ion from their counter anion, tetrafluoroborate, and the corresponding fluorophosphoranes were obtained in good yields.

Stereomutation and apicophilicity of diastereomeric spirophosphoranes (10-P-5)

Abstract The apicophilicity for a series of monodentate groups were determined by deducing activation parameters of equilibration between diastereomeric spirophosphoranes bearing a Martin ligand and a modified Martin ligand. The equilibration was shown to be an intramolecular process and the order of apicophilicity of the groups turned out to be OMe≈H>COMe≈SMe>NMe2>Me>n-Bu on the basis of activation enthalpy. The involvement of π-conjugation type interactions was revealed by X-ray structures of symmetric analogs bearing COMe (acceptor) and NMe2 (donor) groups.