Silaheterocycles 36 (1). Trichlorovinylsilane, lithium-tert-butyl, and 1,3-enynes: A versatile combination for the competitive formation of silacyclobutanes and silacyclobutenes

Equimolar amounts of trichlorovinylsilane (9), lithium-tert-butyl, and 1,3- enynes were reacted to yield the corresponding isomeric silacyclobutanes an d silacyclobutenes competitively. As reaction pathway the mixture 9 BuLi is discussed to give a silene equivalent, Cl2Si=CHCH2 Bu (10), yielding the f our-membered ring silacycles by formal [2 + 2] cycloaddition reactions of 1 0 with the C=C double or the Ctriple bondC triple bond of the 1,3-enyne. Th e relative ratio of the products formed depends on the polarity of the mult iple bonds in the enyne, which is mainly determined by the substituent patt ern. Thus, from the organosubstituted 1,3-enynes (RC)-C-1=C-C(R-2)=(CRR4)-R -3 (R-1=Me, Et, SiMe3, Ph; R-2=H, Me, Ph; R-3=Me, OMe, Ph; R-4=H; and (RC)- C-1=C-R' (R'=1-cyclohexenyl, cyclohexanevinylidyne)) and 9 BuLi the silacyc lobutanes 12, 13, and 15 and the silacyclobutenes 14,16-24, and 27 (from 10 and 3-hexyne) are prepared in a one-step synthesis and isolated from the r eaction mixtures. The silacyclobutanes and -butenes are thermally stable an d can be distilled under vacuo up to temperatures of about 150%C without de composition. The experimental results are confirmed qualitatively by semiem piric calculations at the AM-1 level and their analysis using FMO theory. T he solid state structure of the silacyclobutene 19 (C17H30Cl2Si2) has been determined by single crystal X-ray diffractometry. 19 is orthorhombic, spac e group P2(1)2(1)2(1), a=1030.94(2) pm, b=1244.6(2) pm, c=1605.5(3) pm, Z=4 .