Equimolar amounts of trichlorovinylsilane (9), lithium-tert-butyl, and 1,3-enynes were reacted to yield the corresponding isomeric silacyclobutanes and silacyclobutenes competitively. As reaction pathway the mixture 9/tBuLi is discussed to give a silene equivalent, Cl2Si=CHCH2tBu (10), yielding the four-membered ring silacycles by formal [2 + 2] cycloaddition reactions of 10 with the C=C double or the C=C triple bond of the 1,3-enyne. The relative ratio of the products formed depends on the polarity of the multiple bonds in the enyne, which is mainly determined by the substituent pattern. Thus, from the organosubstituted 1,3-enynes R1 C=C-C(R2)=CR3R4 (R1 = Me, Et, SiMe3, Ph; R2 = H, Me, Ph; R3=Me, OMe, Ph; R4=H; and R1C=C-R' (R' = 1-cyclohexenyl, cyclohexanevinylidyne)) and 9/tBuLi the silacyclobutanes 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 reaction mixtures. The silacyclobutanes and -butenes are thermally stable and can be distilled under vacuo up to temperatures of about 150°C without decomposition. The experimental results are confirmed qualitatively by semiempiric calculations at the AM-1 level and their analysis using FMO theory. The solid state structure of the silacyclobutene 19 (C17H30Cl2Si2) has been determined by single crystal X-ray diffractometry. 19 is orthorhombic, space group P212121, a = 1030.94(2) pm, b = 1244.6(2) pm, c = 1605.5(3) pm, Z = 4.Key words: neopentylsilene, dichloroneopentylsilene, silacyclobutenes, silacyclobutanes, 1,3-enynes.
