N,N-BIS(TRIMETHYLSILYL)YNAMINES - CYCLOADDITION REACTIONS WITH DIMETHYL ACETYLENEDICARBOXYLANE AND KETENES

N,N-Bis(trimethylsilyl)ynamines 1 react with dimethyl acetylenedicarbo xylate (2) in a molar ratio of 1:2 to afford 3-cyclopropenylfurans 3. Configuration and conformation of 3a are confirmed by X-ray crystallog raphy. Addition of a further mol of 1 furnishes the fumarates 4. With ketenes 5 (5c, d are prepared in situ) a competition between the forma tion of cyclic butenone derivatives 6 and allenic imidates 7 is observ ed, depending on the substitution pattern of 1. After hydrolytic worku p, 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 dime thyl acetylenedicarboxylate compared to N,N-dialkyl-substituted ynamin es, yielding furan derivatives instead of anilines. Towards ketenes, h owever, a similar cycloaddition reactivity as for N,N-dialkylynamines is observed.