CYCLOADDITION OF THERMOLYTICALLY GENERATED METHOXYMETHYLSILYLENE TO α,β-UΝSATURATED KETONES AND IMINES

Co-thermolyses of l,2-dimethyl-l,l,2,2-tetramethoxydisilane 1 with 1,4-diheterodienes proceed with unsymmetrical decay of 1 and formal [l+4]-cycloaddition of methoxymethylsilylene to give, e. g., the 1methoxy-l-methyl-l,3,2-dioxasilacyclopentene 2 or the 1,3,2-diazasilacyclopentene 3. Co-thermolytic conversions of 1 with unsaturated ketones or imines, however, afford mixtures of double bond isomers, 1oxa-or 1-aza-2-silacyclopent-4-enes and 1-oxa-or l-aza-2-silacvclopent-3-enes 4-9, respectively.The 4-ene isomers are the major products in case of oxa-and N-alkyl-azasilacyclopentenes, the 3-ene isomers dominate in a N-phenyl-azasilacyclopentene.The results can be explained by stepwise cycloadditions of intermediate methoxymethylsilylene via transient oxa-or azasiliranes.

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