[62762-20-3] · C11H16SSi · 1-Phenylthio-1-trimethylsilylethylene · (MW 208.43)
(a reagent for C2 homologation and a Michael acceptor)
Solubility: very sol most organic solvents.
Preparative Methods: by lithiation of Phenyl Vinyl Sulfide with Lithium Diisopropylamide, followed by silylation,1,2 or the base-induced elimination of 2-chloro-1-trimethylsilyl-1-phenylthioethane,2 or the lithiation of ethyl phenyl sulfoxide with LDA followed by silylation,3 or the Pd-catalyzed coupling reactions of trimethylstannyl phenyl sulfide with 1-bromo-1-trimethylsilylethylene.4
Handling, Storage, and Precautions: use in a fume hood.
Organolithiums undergo smooth additions to 1-phenylthio-1-trimethylsilylethylene at low temperature. The resulting adduct anions are stabilized by two anion-stabilizing substituents, phenylthio and trimethylsilyl. They can be quenched with a variety of electrophiles. Sulfines are formed by treatment with Sulfur Dioxide (eq 1),5 phenyl 1-silylalkyl sulfides by hydrolytic quenching with NH4Cl,1 alkanals by oxidation with m-Chloroperbenzoic Acid and subsequent rearrangement reaction (eq 2),6,7 phenyl silylalkyl sulfides by alkylation with a variety of alkylating agents,8 and vinyl sulfides by condensation with aldehydes.8
When activated with Lewis acid catalysts or silver ion, 1-phenylthio-1-trimethylsilylethylene reacts with a,b-unsaturated acid chlorides at a low temperature in CH2Cl2.2,9 The cation intermediates undergo a silicon-directed Nazarov cyclization to give 3-phenylthio-substituted cyclopentenone derivatives (eq 3). The phenylthio moiety at the b-position of cyclopentenones can be effectively utilized for the introduction of an alkyl substituent by addition/elimination.
Although the adduct anions formed by addition of organolithiums to 1-phenylthio-1-trimethylsilylethylene have high stability at low temperature, at higher temperatures (0 °C) in THF the anions may react with another molecule of 1-phenylthio-1-trimethylsilylethylene. The final anions undergo intramolecular alkylation under the reaction conditions to give cyclopropane derivatives in high yields (eq 4).10 Employment of sulfur-stabilized anions as donor molecules is even more effective (eq 5).11
The benzyllithium intermediates formed by metalation of o-toluamide derivatives with LDA at -78 °C react with 1-trimethylsilyl-1-phenylthioethylene. The resulting adduct anions undergo intramolecular cyclization on to the adjacent amide moiety to provide a convenient route for cyclohexanone annulation (eq 6).12
1-Phenylsulfinyl-1-trimethylsilylethylene (1)2 and 1-phenylsulfonyl-1-trimethylsilylethylene (2) are used as synthetic analogs of 1-phenylthio-1-trimethylsilylethylene. The sulfoxide (1) is an electron-deficient alkene so it is a highly reactive dienophile in Diels-Alder reactions. The cycloadduct with Cyclopentadiene undergoes the sila-Pummerer rearrangement to a thioacetal, which is then hydrolyzed to the ketone (eq 7).6 By this sequence, (1) becomes a useful synthetic equivalent of ketene. The sulfone (2) works as an excellent acceptor molecule for the Michael addition reactions using the aryllithium donors generated by the directed lithiation of o-chloroarenes. The adducts then undergo intramolecular cyclizations by the aid of metal amides to offer an excellent entry to benzocyclobutene derivatives.13
Kyushu University, Kasuga, Japan