Reactions of Group IV organometallic compounds. Part XXVI. Insertion reactions of isocyanates and isothiocyanates to N-trimethylsilyl-(diphenylmethylene)amine and subsequent [4 + 2] cycloadditions of isocyanates with their adducts

Abstract

N-Trimethylsilyl(diphenylmethylene)amine reacted with 1 mol. equiv. of methyl, phenyl, or benzoyl isocyanate, and with the corresponding isothiocyanates, by the selective cleavage of the Si–N bond. The n.m.r. spectra of the 1:1 insertion product (III)–(VIII) showed the non-equivalency of trimethylsilyl proton signals at low temperature. The concept of 1,3-transfer of the trimethylsilyl group was preferred to that of hindered rotation about the C–N bond for the interpretation of these splittings. With 2 mol. equiv. of methyl or phenyl isocyanate, the silylamine gave the 1,3-substituted 3,4-dihydro-4,4-diphenyl-6-trimethylsilyloxy-1,3,5-triazin-2(1H)-ones (XVIII) by [4 + 2] cyclo additions of isocyanates with the imidate form (B) of the 1:1 adducts.