Organisch-Chemisches Institut der Universität Wien, Österreich A-1090, Währingerstrasse 38 Austria
Abstract:
The first step in the reaction of trimethylsilylmethylene-dimethylsulfurane 1 (prepared from (CH3)3SiCH2S?(CH3)2ī with 1 equivalent (CH3)3COK) with carbonyl compounds (R1)(R2)CHCOCH2R32 leads Peterson-like way to the non-isolable vinylsulfoniumdimethylsilanolate-intermediate B or its recombined product A. Depending on the reaction conditions and the nature of the substituents R1, R2 and R3 there exist five different pathways to the end products 3–7. Frequently one can find an elimination of trimethylsilanole followed by a 2,3-sigmatropic rearrangement of an allyl-substituted methylene - sulfurane - intermediate to the 2,3,3 - trialkyl - 5 -thiahex -1 - enes 3 CH3SCH2C(R1)(R2)C(CH2R3)=CH2]. Sometimes this formation of 3 is suppressed by means of two equivalents of (CH3)3COK. In this case demethylation of the assumed precursor B arises yielding the E,Z-vinylsulfides 4 CH3SCH=C(CH2R3)(CHR1R2)], whereas the formation of the methylthiomethyl-dialkylcar-binoles 5 CH3SCH2C(OH)(CH2R3)(CHR1R2)] can be explained by the demethylation of the precursor A. Treatment with five equivalents of (CH3)3COK yields in one case the 2,2,5,7 - tetramethyl - 5 - hydroxy - 3 - oxaoctane (7a) as a consequence of a extrusion of dimethylsulfide. Frequently also epoxides of type 6 CH2-C(CH2R3)(CHR1R2)] can be isolated. Their formation is compared with the well-known preparation of epoxides by the dimethylsulfonium-methylide on the one and dimethylsulfoxoniummethylide on the other side.