N,N ‐Bis(trimethylsilyl)ynamines: Cycloaddition Reactions with Dimethyl Acetylenedicarboxylate and Ketenes

N , N ‐Bis(trimethylsilyl)ynamines 1 react with dimethyl acetylenedicarboxylate ( 2 ) in a molar ratio of 1:2 to afford 3‐cyclopropenylfurans 3 . Configuration and conformation of 3a are confirmed by X‐ray crystallography. Addition of a further mol of 1 furnishes the fumarates 4 . With ketenes 5 ( 5c , d are prepared in situ) a competition between the formation of cyclic butenone derivatives 6 and allenic imidates 7 is observed, depending on the substitution pattern of 1 . After hydrolytic workup, the corresponding amides 10 or the vinylogous amides 9 are obtained in good yield. These experiments indicate that the silylated ynamines 1 show a completely different, more selective reactivity towards dimethyl acetylenedicarboxylate compared to N , N ‐dialkyl‐substituted ynamines, yielding furan derivatives instead of anilines. Towards ketenes, however, a similar cycloaddition reactivity as for N , N ‐dialkylynamines is observed.