SILAHETEROCYCLES .28. FACILE SYNTHESIS OF SILACYCLOBUTENES FROM SILENE ACETYLENE [2+2] CYCLOADDITION REACTIONS

The dichlorosilyl substituted silenes Cl2Si=CHCH2-t-Bu (2a) and Cl2Si=C(Ph)CH2-t-Bu (2b) and the bis(trimethylsiloxy) substituted derivative (Me3SiO)2Si=CHCH2-t-Bu (2c) are formed from reactions of the corresponding chlorovinylsilanes Cl3SiCH=CH2 (1a), Cl3SiC(Ph)=CH2 (1b), and (Me3SiO)2Si(Cl)CH=CH2 (1c) with Li-t-Bu. The reaction of the silenes with a variety of diorgano substituted acetylenes R3C=CR4 (R3, R4 = Me, SiMe3, Ph) yields the silacyclobutenes 4a-9c in a one step procedure; in some cases the ene products 5alpha-8gamma are formed in competition with the silene [2 + 2] cycloadducts. The substitution at C4 of the silacyclobutene skeleton can be modified, when different silene units are used (e.g. 2a --> 2b), while the substitution pattern at C2 and C3 will be modified by the use of different acetylenes. The dichlorosilyl functionality can be utilized for the synthesis of silicon substituted derivatives by simple reaction sequences. The silacylobutenes are thermally surprisingly stable and can be distilled in most cases under vacuum at temperatures up to 200-degrees-C without decomposition.