Cyanoketenes with alkynes

The addition reactions of cyanoketenes with alkynes have already been discussed. Cyanoketenes, however, also undergo reaction with ketenes, the reaction pathway depending on the structure of the ketene. ... 

Alkynyl cyanoketenes readily undergo [2+2] cycloadditions with alkenes, and the reaction has now been extended to alkynes ". The initial reaction is conventional, 71 forming 72. However, 72 can then rearrange to form the dibenzopyran, 74. 

Cyanoketenes, N=C—CH=C—O, have the tendency to react with alkenes and alkynes to yield a cycloaddition product. Because the ketenic carbonyl carbon has electrophilic character, the reagent will behave as an electrophile. The -butyl derivative, N=C—C( -Bu)=C=0, has received the most attention. Its reactions with alkenes and alkynes have been reviewed by Moore and Gheorghiu. The additions occur either in a 2n +2n concerted fashion or through a zwitterionic intermediate. Moore and coworkers also studied the cycloaddition of chlorocyanoketene to alkynes ". ... 

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