THE SYNTHESIS AND DIMERIZATION OF TRANSIENT 1-SILABUTADIENES

3-Methyl-1-tris(trimethylsilyl)silyl-2-butenol(1) (6) and 3-Phenyl-1-t ris(trimethylsilyl)silyl-2-propenol(1) (7) were prepared by the reacti on of tris (trimethylsilyl) silyllithium (5) with 3,3-dimethylacrolein and (E)-cinnamaldehyde, resp. The alcohols 6 and 7 proved to be suita ble precursors for the generation of the transient 1-silabutadienes (M e(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 temperatu res eliminated trimethylsilanolate and gave 8 and 9, which were trappe d 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 quantiti es 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., besi des polymeric material. Treatment of the alcohol 6 with MeLi in tetrah ydrofuran caused a 1,3-Si,O-trimethylsilyl shift affording the alkoxys ilane (Me(3)Si)(2)SiH-CH(OSiMe(3))CH=CMe(2) 19.