Formation of 1-aza-2-silacyclopentanes and unexpected products from the insertion of phenylisocyanate into 2,2-dimethyl-1-(trimethylsilyl)-1-aza-2-silacyclopentane
by intramolecular condensation reactions and substitution reactions at the silicon atom. The products tend to undergo ring-opening polymerisation. In contrast to literature reports, they can only be isolated as N-substituted derivatives. Phenylisocyanate inserts into the Si-N bonds of cyclic aminosilanes to form seven-membered heterocycles. Furthermore, phenylisocyanate reacts with N-H bonds in the same