Reaction with vinyl sulfide anions

Synthesis of Vinyl Sulfides. Anion (2) adds to aldehydes, ketones, and enones, in the last-named case in either 1,2- or 1,4-manner depending on the reaction conditions.In the case of 1,2-addition the -hydroxysilane adduct usually cannot be isolated owing to rapid elimination (Peterson alkenation) to vinyl sulfides (eq 5), which can be hydrolyzed to the corresponding aldehydes. The vinyl sulfides are not formed stereoselectively unless there are proximate bulky substituents. Peterson alkenation products have also been observed in the reaction of (2) with amides, ureas, and carbonates. ... 

B. Preparation of Vinyl Sulfides by the Reaction of (Phenylthio)carbenes with Nitrile Anions... 

An explanatory mechanism for the formation of vinyl sulfides is shown in Scheme 24. In route a, (phenylthio)carbene 77 generated from chlorosulfide 75 reacts with the nitrile anion to form (phenylthio)carbanion 79, which then undergoes elimination of cyanide ion to produce vinyl sulfide 76. In route b, 75 reacts first with the nitrile anion 74 to produce P-(phenylthio)nitrile 78 followed by base-catalyzed P-elimination. However, route b is unlikely because 79 cannot be generated from 68 due to a larger pKa value of its ot proton than that of the nitrile. In fact, the reaction of chlorosulfide 75a with lithionitrile 80 gave a different product 81 in 63% yield. 

Ketone synthesisAddition of an alkyl- or aryllithium to 1 forms an anion (a) that undergoes a Wittig-Horner reaction with an aldehyde to form a vinyl sulfide (2),... 

Since the sulfide substituents can be removed reductively, the cyclisations of 273 and 276 are synthetically equivalent to cyclisations onto disubstituted double bonds, giving compounds such as 275.142>143 Like the corresponding cyclisations onto monosubstituted alkenes they are highly stereoselective, with the sense of stereoselectivity being solvent-dependent the products 274 and 277 are trans as shown for a cyclisation conducted in THF in pentane complete cis selectivity is obtained. Similar cyclisations onto vinyl sulfides have been used to explore the stereochemical course of the anionic cyclisation reaction, and are discussed below.146... 

Pentannelation (6,208-209). The deprotonation of vinyl sulfides such as 1 was originally thought to afford allyl anions (2). Actually, the vinyl hydrogen is abstracted instead. The resulting anions 3 undergo cycloaddition reactions with unsaturated O OH O-----Li... 

PhenyIthiovinyllithium, CH2=CSC6H5 (1), 8, 281. The anion can be obtained conveniently by reaction of phenyl vinyl sulfide in THF with n-butyllithium and TMEDA at -90 . 

In the original study by Peterson, the alkenation procedure was found to be compatible with sulfur and phosphorus substitution. The alkenation reaction has been tqrplied successfully to a variety of substituted alkenes. Because of the aiuon-stabilizing nature of the thiophenyl, the p-hydroxysiliuie is not isolated and the elimination to the alkene takes place directly to form a 1 1 mixture of ( )- and (Z)-isomers. Ager studied the reaction of the lithio anions of phenyl (trimethylsilyl)methyl sulfides (318) with a variety of carbonyl compounds (equation 72). Yields of this process were good, and addition occurred even with enolizable substrates. This reaction was extended to vinyl sulfones. In contrast to the sulfide case, the substituted sulfone silyl anion behaves as a base, leading to undesired enolization. The best yields were observed for the case where R is a hydrogen or phenyl. 

Vinyl sulfides and selenides can be alkylated efficiently at the a-position in a two step-one pot reaction which involves their a-metallation and further reaction of the resulting anion with alkyl halides. 

Elimination of Thiophenol from Thioacetals. Conversion of thioacetals to vinyl sulfides is accomplished under exceptionally mild conditions by treatment with (CuOTOa-CeHe (eq 45). The reaction involves an a-phenylthio carbocation intermediate. Three factors contribute to the effectiveness of this synthetic method the Lewis acidity of a copperfT) cation that is unencumbered by a strongly coordinated counter anion, the solubility of the copper(I) triflate-benzene complex, and the insolubility of CuSPh in the reaction mixture. An analogous elimination reaction provides an effective route to phenylthio enol ethers from ketones (eq 46). ... 

Synthesis of Vinyl Sulfides. Treatment of furanoses with anion 2 induced the ring-opening reaction via addition to the aldehyde of the omega hydroxy aldehyde in equilibrium followed by the rapid elimination of the /8-hydroxysilane which afforded vinyl sulfides (eq 12) in moderate yields (50-61%) with poor stereoselectivity (ElZ 2 3). Alternatively, modified Horner-Wittig reactions afforded the desired products in much higher yields (72-100%) with improved selectivity for the E-stereoisomer (E/Z, as high as 17 1). 

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