Cyanoketenes with ketenes

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. ... 

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. ... 

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... 

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 ". ... 

Another new -lactam synthesis proceeds via the hitherto unknown chloro-cyanoketene, obtained by thermolysis of various /8-azidoenones. Hence, when the crotonolactone (160) was refluxed in benzene in the presence of dicyclohexyl-carbodi-imide 88% of the adduct (161) was obtained similarly thermolysis of (160) with ethoxymethylene aniline gave 48% of (162). The reactions are stereospecific, and only one diastereoisomer was obtained. Thermolysis of 4-azidopyrrolin-3-one (163) in benzene gave 58% of the j8-lactam (165) directly, the zwitterion (164) being implicated without direct evidence such intermediates have already been proposed as precursors of jS-lactams when ketenes add to imines. The f -stereo-... 

---