The Synthesis and Dimerization of Transient 1‐Silabutadienes

3‐Methyl‐1‐tris(trimethylsilyl)silyl‐2‐butenol(1) ( 6 ) and (E)‐3‐Phenyl‐1‐tris(trimethylsilyl)silyl‐2‐propenol(1) ( 7 ) were prepared by the reaction of tris(trimethylsilyl)silyllithium ( 5 ) with 3,3‐dimethylacrolein and (E)‐cinnamaldehyde, resp. The alcohols 6 and 7 proved to be suitable precursors for the generation of the transient 1‐silabutadienes (Me 3 Si) 2 Si = CHCH = CR 1 R 2 8 and 9 ( 8 : R 1 = R 2 = Me; 9 : R 1 = H, R 2 = Ph) following the principle of the modified Peterson reaction. Thus, 6 and 7 after deprotonation with excess MeLi in ether at low temperatures eliminated trimethylsilanolate and gave 8 and 9 , which were trapped by the excess organolithium reagent undergoing nucleophilic 1,2‐ or 1,4‐addition reactions. In the absence of scavengers, e.g. when 8 and 9 were generated by treatment of 6 and 7 with stoichiometric quantities of MeLi in ether, the 1‐silabutadienes dimerize in a [2 + 2] head‐to‐head fashion to give the 1,2‐disilacyclobutanes 17 and 18 , resp., besides polymeric material. Treatment of the alcohol 6 with MeLi in tetrahydrofuran caused a 1,3‐Si,O‐trimethylsilyl shift affording the alkoxysilane (Me 3 Si) 2 SiHCH(OSiMe 3 )CH = CMe 2 19 .