Organometallic reactions. Part VI. The addition of the Sn–O bond to the carbonyl group

Abstract

Tributyltin methoxide and bistributyltin oxide react at the carbonyl group of many aldehydes and of certain more reactive ketones to give the 1 : 1 adducts (A). In the case of chloral and of 1,1,3-trichloro-1,3,3-trifluoropropane-2-one, the n.m.r. spectra show that 1 : 2 adducts (B) can also be formed, and, with chloral, repetition of this process gives the polymer (C). R₃Sn·OR[graphic omitted]R₃Sn·O·CR″R″′·OR′[graphic omitted] (A) R₃Sn·[O·CR″R″′]₂·OR′[graphic omitted]R₃Sn·[O·CR″R″′]_a·OR′(B)(C) The 1 : 1 adduct (A) can alternatively react with other carbonyl compounds by a reversible exchange of the organotin reagent. Acetyl chloride or methanol similarly react by displacing the carbonyl compound OCR″R‴. If one or both of the groups R″ and R‴ is a trihalogenomethyl group, methanolysis can alternatively involve displacement of the carbonyl compound R″CO·OR′, liberating the haloform; in consequence, organotin compounds catalyse the methanolysis of hexachloroacetone to methyl trichloroacetate and chloroform. It is suggested that all these reactions proceed through a 6-membered cyclic transition state.