Cyanoketenes cycloadditions

Another reactive ketene which undergoes efficient cycloaddition with allenes is tert-butyl-cyanoketene (TBCK). Again mixtures of isomeric cycloadducts are obtained when unsymmet-rically substituted or 1,3-disubstituted allenes are employed.10-12... 

The unusual incorporation of the cyano group of l-butyl cyano ketene was observed in the reaction of an azomethine with excess of r-butyl cyanoketene resulting in pyrimido[6,l-d][l,3,5] dioxazine (29). It was said to proceed via an intermediate adduct (98), which further underwent [2 + 2 + 2] cycloaddition in the presence of two molecules of ketene (Scheme 10) <78CC820). 4-Isothiocyanato-4-methyl-2-pentanone and A -(2-hydroxyethyl)hydrazine in refluxing ethanol led to... 

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. 

Acrylonitrileundergoes a [2+2] cycloaddition reaction with ketene alkylsilyl acetals. Like cyanoketenes, cyanoacetylenes readily undergo cycloaddition reactions, and research was given an additional stimulus by their observation in the atmosphere of Titan. ... 

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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