Synthesis and applications of chiral organoboranes generated from sulfonium ylides

The reactions of aryl-stabilized sulfonium ylides with trialkyl/triarylboranes have been investigated. Clean monohomologation of the boranes with only a small amount of the higher homologation products (<10%) was observed. The homologation products were isolated as the alcohols (treatment with H2O2/NaOH) and amines (treatment with NH2OSO3H). Although the reactions were conveniently conducted at 5 degrees C, the ylide reaction with tributylborane was very fast even at -78 degrees C (complete after 15 min). Use of chiral sulfides rendered the reactions asymmetric, and high enantioselectivity (>95% ee) was observed in all cases. The ylide-borane reaction was applied to short syntheses of the anti-inflammatory agents neobenodine and cetirizine, both of which contain a chiral diarylmethylalkoxy and diarylmethylamino moiety, respectively.     

Synthesis of some sulfonium salts and ylides containing the isoxazole nucleus

Some dimethylisoxazolylmethylsulfonium salts and the corresponding ylides were synthetized and their chemical behaviour studied. Dimethylsullonium-5-isoxazolyl methylides (XIa,b) give 5-isoxazolyloxiranes (XIIa,d) and XIII when allowed to react with carbonyl compounds. Ring opening products from these oxiranes are also reported.     

Spectra and structure of sulfonium C-mononitro ylides

Conclusions Based on the data of the vibrational spectra and quantum-chemical calculation, in its electronic structure the nitro group in sulfonium C-nitro ylides is closer to the nitro groups in nonionized nitro compounds than in their salts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1403–1406, June, 1981.     

Spectra and structure of sulfonium C-dinitro ylides

Conclusions Based on the data of the vibrational spectra of sulfonium C-dinitro ylides and the quantum-chemical calculation of the electronic structure of the molecule the nitro groups of dinitro ylides in their electronic structure differ substantially from the nitro groups of both the gem-dinitroalkanes and their salts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1407–1409, June, 1981.     

Stereochemistry of methylation of cyclic sulfonium ylides

Low temperature methylation of 6-membered sulfonium ylides is highly stereoselective and configurational inversion has been established in at least one case. No appreciable stereoselectivity has been observed in 5-membered ylides.     

Carbon-13 NMR spectroscopy of sulfonium ylides

C-13 NMR data for a series of stabilized and unstabilized ylides indicate flattening at the ylidic carbon with respect to the parent salts. For unstabilized ylides association between the carbanionic center and the lithium cation cannot be neglected.     

硫叶立德途径立体控制合成乙烯基型环氧化合物

在相转移条件下(CH3CN/KOH/RT)乙烯基型硫叶立德和醛反应高产率地得到以反式为主的产物,而在低温溴化锂存在下(LiBr/KHMDS/THF/-90℃)得到以顺式为主的产物,对于通过反应条件的变换而改变反应产物立体化学的机理,给出了一个初步的解释。     

Sulfur ylides. 5. Reactions of phthalimide-containing keto-stabilized sulfonium ylides

Some reactions of phthalimide-containing keto-stabilized sulfur ylides have been investigated. It was established that in addition to the formation of the usual products for keto-stabilized sulfur ylides, the reaction with acrylonitrile is accompanied by a rearrangement and leads to 1,1-disubstituted cyclopropanes.Institute of Chemistry, Bashkir Science Center, Urals Branch, Russian Academy of Sciences, 450054 Ufa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 720–726, March, 1992.     

Reaction of sulfonium ylides complexed with tricarbonylchromium

Oxiranes and olefins are obtained from the reactions of free and complexed phenylmethylsulfonium methylides with tricarbonylchromium with benzophenone, benzaldehyde and cyclohexanone. Good yields of olefins are obtained from the Cr(CO)₃ complexes with benzophenone, but yields of 0.1-0.5% are obtained with benzaldehyde and cyclohexanone.     

Reactions of distabilized β-dicarbonyl sulfonium and iodonium ylides with isocyanates

The reactions of tosyl isocyanate with diethyl diphenylsulfuranylidenemalonate, 2-dimethylsulfuranylidenedimedone, and 2-dimethylsulfuranylideneindane-1,3-dione afforded 1,3-ditosyl-5,5-diethoxycarbonylimidazolidine-2,4-dione and tosylimination products at the keto groups, respectively. Phenyliodonium ylides derived from diethyl malonate and ethyl acetate react with 3,4-dichlorophenyl isocyanate to form substituted oxazolin-2-ones. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 854–861, May, 2006.     

The structure of sulfonium ylides stabilized by the malonylide moiety

The crystal structures of four thioxanthenium bis(carbomethoxy)methylides and methylides of di-(p-nitro-phenyl)sulfonium and dimethylsulfonium have been determined. The carbanion moiety in all cases is planar and the pi-system is rotated 90° with respect to the sulfur lone pair. All compounds exhibit a pseudo-equatorial orientation of the carbanion system except for the 2,4-dimethylthioxanthenium ylide. The compounds are described in terms of the geometries around the sulfur atom, the interplanar angles and sulfur-oxygen and oxygen-oxygen interactions. Surprisingly, the sulfur atom is not symmetrically placed with respect to the two phenyl rings in the thioxanthenium compounds. The sulfur is coplanar with one phenyl ring but is significantly out of the plane of the other. The ¹³C and ¹H spectra of the ylides are discussed along with the temperature dependence which indicates restricted rotation about the ⁺S? C^? bond in several cases. The factors contributing to the stability of the ylides are analyzed.     

Asymmetric synthesis of cyclopropyl phosphonates using chiral terpenyl sulfonium and selenonium ylides

The asymmetric cyclopropanation of a vinylphosphonate using optically active sulfonium and selenonium ylides derived from (−)-menthol and (+)-limonene was developed. The ylides were generated in situ by the reaction of the corresponding sulfonium or selenonium salt in the presence of potassium carbonate or DBU as a base. The transfer of the CHPh and CHCO₂Et groups into the cyclopropane ring showed moderate diastereoselectivity and excellent enantioselectivity (up to 99:1) for the trans- and cis-products. The absolute configuration of phenyl cyclopropyl was assigned based on comparison to their tolyl analogues.     

Photocationic and radical polymerizations of epoxides and acrylates by novel sulfonium salts

Novel sulfonium salts [methyl‐, 2‐indany‐, or 1‐ethoxycarbonylethyl methyl‐2‐naphthylsulfonium hexafluorophosphate and 2‐indany‐, 1‐ethoxycarbonylethyl‐, 2‐methyl‐2‐phenylpropyl‐, 2‐phenylpropyl‐, 2‐phenylethyl‐, 2‐(4‐methoxyphenyl)‐ethyl‐, or 3‐(4‐methoxyphenyl)‐2‐propyl methylphenylsulfonium hexafluorophosphates] were synthesized by the reaction of dimethylsulfate and the corresponding sulfides followed by anion exchange with KPF₆. These sulfonium salts could polymerize epoxy monomers at lower temperatures than previously reported for benzylsulfonium salt initiators. In particular, sulfonium salts with naphthyl groups showed higher photoactivity than already reported for di(4‐tert‐butylphenyl)iodonium and triphenylsulfonium hexafluorophosphates. These sulfonium salts showed higher activity in photoradical polymerization and photocationic polymerization. The photopolymerization was accelerated by the addition of 4‐methoxy‐1‐naphthol, N‐ethylcarbazole, 2,4‐dimethylthioxanthone, phenothiazine, and 2‐ethyl‐9,10‐dimethoxyanthracene as photosensitizers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3816–3827, 2003     

Carbon-carbon bond-forming reaction of cyclic sulfonium ylides stabilized by a carbonyl group

Rhodium(II)-catalyzed decomposition of diazoketones 1 and 5 bearing a cyclic dithioacetal, in the presence of aldehyde and ClTi(Oi-Pr)(3), afforded both or one of the C=C-bonded products, i.e., ring-enlarged enone 2 and ring-transformed thiophenone 3, that were formed between aldehyde and intermediate bicyclosulfonium ylide. The stereochemistry of the exocyclic C=C bond in the products was exclusively Z. The sulfonium atom that transiently composed the ylide was incorporated into products, but no oxirane was formed.     

Discriminating non-ylidic carbon-sulfur bond cleavages of sulfonium ylides for alkylation and arylation reactions

A sulfonium ylide participated alkylation and arylation under transition-metal free conditions is described. The disparate reaction pattern allowed the separate activation of non-ylidic S-alkyl and S-aryl bond. Under acidic conditions, sulfonium ylides serve as alkyl cation precursors which facilitate the alkylations. While under alkaline conditions, cleavage of non-ylidic S-aryl bond produces O-arylated compounds efficiently. The robustness of the protocols were established by the excellent com...