Insertion of CO2, COS and CS2 into the N-Si bond of extremely electron-rich 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine and formation of a new poly(N,S) heterocyclic system by multiple cycloaddition. Journal of Organometallic Chemistry, (501)1-2:283--292, 1995. [PUMA: bond carbon carbonyl crystal cycloaddn dioxide disulfide insertion mol nitrogen prepn pyrazine silicon silicon;sulfide silyl;diepiazanothiocinopyrazinethione structure;insertion sulfide]