[17872-92-3] · C10H16O2SSi · Phenylsulfonyl(trimethylsilyl)methane · (MW 228.42)
(the lithio anion reacts with carbonyl compounds to afford vinyl sulfones2 via a modified Peterson alkenation procedure;3 double alkylation, reduction, and sila-Pummerer rearrangement provides ketones4)
Alternate Name: phenyl trimethylsilylmethyl sulfone.
Physical Data: mp 28-30 °C; bp 121 °C/0.01 mmHg.
Solubility: readily sol THF, DME, ether.
Form Supplied in: white solid; widely available.
Preparative Method: can be readily prepared via several routes,5 of which the most suitable for large-scale preparation involves the reaction of sodium thiophenolate with (Chloromethyl)trimethylsilane, the sulfide obtained then being oxidized to the sulfone with buffered Peracetic Acid.6
Purification: distillation under reduced pressure.
Handling, Storage, and Precautions: store under an inert atmosphere at 0-4 °C.
The Peterson alkenation reaction provides a useful method for the preparation of alkenes.3 The scope of the reaction can be expanded to give a-heterosubstituted alkenes by the use of a-heteroatom-substituted carbanions. The lithio anion generated from the title reagent (1) reacts with carbonyl compounds to give the corresponding vinyl sulfones via a modified Peterson alkenation procedure (eq 1).2,5,7,8 Both aldehydes and ketones are suitable substrates, although complications can arise when enolizable ketones are employed.5 The solvent has a marked effect on the reaction, with the highest yields being obtained with DME.5
The reaction can tolerate a wide range of functionality, including ethers, esters, and epoxides. The vinyl sulfones are generally obtained as mixtures of (E) and (Z) isomers, although the degree of selectivity is highly substrate dependent.5,9 The aldehyde (2) was converted to the corresponding vinyl sulfone as a single (E) isomer in 96% yield. The vinyl sulfone obtained is an intermediate in the total synthesis of the antifeedant ajugarin I (eq 2).10
The use of ether as solvent allows the trapping of the intermediate alkoxide by acetylation.5 The b-acetoxy-a-silyl sulfone (3), isolated from the reaction of benzaldehyde and the lithium anion of (1) followed by trapping with Acetic Anhydride (eq 3), was shown by NMR to be a single diastereoisomer. However, attempted stereospecific elimination was found to give mixtures of (E)- and (Z)-sulfones.5
Greater (E) stereoselectivity can be achieved in the preparation of vinyl sulfones from carbonyl compounds by the use of the related a-sulfonylphosphonates.11
a-Silyl sulfides undergo sila-Pummerer rearrangement to provide aldehydes and ketones.12 Access to the ketones is inhibited by the difficulty in deprotonating and hence alkylating the a-silyl sulfides. The a-silyl sulfone (1) is readily deprotonated with n-Butyllithium and subsequent alkylation with an alkyl halide proceeds smoothly.13 The process can be repeated a second time to provide dialkylated a-silyl sulfones (eq 4).4
The lithio anion is formed in THF at 0 °C and can be alkylated with a range of simple alkyl and alkenyl halides. The a-silyl sulfones thus obtained are then reduced with either Diisobutylaluminum Hydride or Lithium Aluminum Hydride to give a-silyl sulfides capable of undergoing the sila-Pummerer rearrangement.4
a-Silyl sulfone (1) can be doubly deprotonated by the use of a second equivalent of n-BuLi.14 Reaction of the dianion (4) with Dichlorotitanium Diisopropoxide prior to reaction with benzaldehyde provides the a-silylvinyl sulfone (eq 5). The a-silylvinyl sulfone is obtained in good yield as a 2:1 mixture of (E) and (Z) isomers.14a
The lithio anion of (1) also reacts with simple amides to provide 2-aminovinyl sulfones.15 Deprotonation is performed with Lithium Diisopropylamide at -70 °C in THF, and the resultant 2-aminovinyl sulfones are obtained in moderate to good yields with excellent (E) selectivity.
Steven V. Ley & Michael C. Willis
University of Cambridge, UK