[62761-90-4] · C13H24SSi2 · Phenylthiobis(trimethylsilyl)methane · (MW 268.62)
(formation of vinylsilanes and as a methoxycarbonyl anion equivalent)
Physical Data: bp 88 °C/0.16 mmHg.
Solubility: sol most common organic solvents.
Analysis of Reagent Purity: 1H NMR.
Preparative Method: synthesized from phenylthiotrimethylsilylmethane.2
Handling, Storage, and Precautions: use in a fume hood.
The most general utility of the title reagent (1) involves Peterson alkenation reactions. Deprotonation of this reagent, followed by addition to carbonyl-containing substrates, affords phenylthiovinylsilanes (eq 1).3
The reduction of the carbon-sulfur bond in (1) with Lithium Naphthalenide also produces an alkenation reagent (eq 2).4 This protocol is limited, however, to use with nonenolizable ketones and aldehydes. Lithiobis(trimethylsilyl)methane, the active intermediate in this reaction, can also be produced through the deprotonation of Bis(trimethylsilyl)methane.
When (1) is treated with a fluoride source, a mild alkenation reagent is produced (eq 3).5 The efficient transformation of enolizable ketones and aldehydes under these conditions, as opposed to the lithium naphthalenide reduction process, aptly demonstrates this fact.
The lithium anion of (1) adds exclusively in Michael fashion to cyclohexenone (eq 4).6 In comparison, lithiobis(phenylthio)methane predominantly adds to the carbonyl, providing a 2:1 mixture of the possible regioisomers. As with many other 1,4-conjugate additions, substitution at the alkene terminus alters the reaction regioselectivity (eq 5).6
Styrene oxide reacts with lithiophenylthiobis(trimethylsilyl)methane to afford cyclopropane-containing products (eq 6).7 This reaction is limited, due to the complexity of its mechanism: the alkenation reagent must serve to generate both alkenic and carbenic species. For this reason, only styrene oxide and trimethylsilyloxirane undergo this transformation.
The alkylation of lithiophenylthiobis(trimethylsilyl)methane with an alkyl halide, followed by electrochemical oxidation of the resulting thiobis(silane), provides a homologated methyl ester (eq 7).8 The electrochemical oxidation, due to its mild nature, can be tolerated by a wide variety of functional groups.
Jeffrey A. McKinney
Zeneca Pharmaceuticals, Wilmington, DE, USA