Ynamines ketenimines

The use of ynamines, ketenimines and mercuric acetate as electrophiles in DMSO oxidations has also been reported but, as yet, appear to offer no advantages over the reagents described above. 

Some examples dealing with the [4 + 2] cycloaddition of ketenimines have been recorded (Scheme 58). Thus, thioketones and ynamines reacted with N-aryl ketenimines 257 through the carbon—nitrogen and the conjugated aromatic carbon—carbon double bonds to yield benzothiazine derivatives 258 (80JOC3766 82JOC3998) and substituted quinolines 259 (73JA5417), respectively. Simple ketenimines 261 were formed by reaction... 

In the absence of dipolarophiles the intermediate loses sulfur to give the carbodiimide however, the intermediate may be trapped with a number of alkenes, heterocumulenes and other reagents such as ynamines, ketenes, isocyanates, isothiocyanates, carbodiimides, ketenimines, sulfonylimines, imines, nitriles, thiocarbonyl compounds, Wittig reagents and the already mentioned enamines (80AG277). Contemporary knowledge of the chemistry of these sulfonyliminothiatriazolines is mainly due to the meticulous work of L abbe and his coworkers (80AG277). 

Metal ynamines (metal ynamides, 180) are aza-analogues of metal ynolates and have not been studied as well as the ynamines (181), in spite of being much more reactive than the latter. l,4-Diphenyl-l,2,3-triazolyllithium (183), prepared by lithiation of 1,4-diphenyl-1,2,3-triazole (182), is converted into lithium ynamine (lithium ynamide) (184) on thermal elimination of nitrogen (equation 72). This ynamine (184) is methylated in moderate yields either by methyl iodide to give a ketenimine (185) and a dimerization product (186), or... 

The silylated lithium ynamine 192 is generated by metaUation with BuLi of 5 -methyl Af-phenyl-trimethylsilylethanimidothioate (190), via a ketenimine intermediate (191), as shown in equation 75. The interconversion between 191 and 192 can be discerned by silylation taking place at both the N- and -positions to afford the Af-silylynamide 193 and the bis(/ -silyl)ketenimine 194. In equation 76 are shown three possible synthetic... 

There are only few reports of [2 + 2] cycloadditions with ketenimines. " In most cases, reactions occur across the C=C bond. Only ynamines and polyfluorinated alkenes cycloadd to the C=N bond. 

Few reactions of alkynes with C—X bonds are valuable for the preparation of four-membered hetero-cycles. Ynatnines react with aldehydes and ketones in the presence of Lewis acids to give unstable oxetene derivatives which undergo electrocyclic opening (Scheme 43). Open-chain products are also obtained with thiocarbonyl compounds,Schiff bases and iminium salts. Reactions of ynamines with carbon dioxide, ketenes, - ketenimines and isocyanates " often give mixtures of products and are of little preparative value. 

The addition of fer/-butyl isocyanide to the cyclopropene 1 leads eventually to a ketenimine 2, apparently by ring opening of an intermediate dipolar species. Reaction with ynamines has also been reported. ... 

The cyclopropenone (130) undergoes decarbonylation on flash photolysis in water.The resultant ynamine (131) is accompanied by the enamine (132). The enamine is formed from the carbene (133) and its trapping with water. The ynamine (131) is unstable and transforms into the ketenimine (134). The photo-... 

An isodesmic reaction has been employed to study substituent effects on the stability of ketenimines, XCH=C=NH. A (negative) correlation with the electronegativity of the substituent X was found. The sensitivity to the substituent effect is less than that for ketenes or isocyanates, but more than that found for diazomethanes or allenes. Particular stabilizing effects are found for tt-acceptors, e.g. X = AIH2, BH2, 0=CH, HO2C, CN, NO2, and HSO2 (suggesting cyano-cation resonance stmctures are important), and for X = Li (i.e. ynamine resonance). 

The proclivity of ynamines towards reaction with carbonyl groups is further illustrated by formation of (138 cis and trans) from addition of (139) to propiolaldehyde and of ketenimines (140) from ynamines and alkyl isocyanates. 

From Af-phenyl substituted ketenimines 15 and ynamines the linear 1 1 adducts 16 are formed, which undergo an intramolecular cyclization reaction to give 4-aminoquinoline derivatives 17. 

The vinyl ketenimines 132 react with ynamines at 0 °C by a [2+2] cycloaddition across the C=N bond to generate the allene 133, which undergoes electrocyclic ring closure to... 

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