Ketenes reactions with azines

Other groups that react with chloromethyleneiminium salts include hydroxylamines, hydrazines, oximes, imines, azines, anhydrides, imides and ketene O-alkyl-O -silyl acetal derivatives however, reactions with these compounds have been relatively infrequent. 

Because of their predictable behavior and reactivity, thioacyl isocyanates comprise the bulk of this work, and extensive studies of their [4 + 2] reactions with olefins,83 enamines,84 enol ethers,843 thioacyl isocyanates,85 imines,85 1 86 carbodiimides,84387 isocyanates,843 azirines,88 /3-enaminoke-tones,89 dianils,86d azines,90 hydrazones,91 imidazoline-4,5-diones,92 aryl cyanates,93 disubstituted cyanamides,93 aldehydes,94 ketones,94 ketenes,94 alkyl or aryl iminodithiocarbonates,95 and the carbon-carbon double bond of ketenimines96 have been detailed. In an extensive comparative study of the [4 + 2] cycloaddition reactions of thioacyl isocyanates, the heterocu-mulenes bearing strong electron-withdrawing substituents were found to be more stable and less prone to participate in cycloaddition reactions.84 Representative examples are summarized in Scheme 9-IV. 

A novel fragmentation of iV-arylidene- or Al-(aLkylideneamino)- 8-lactams can be induced by ozone to lead to various enol ethers after a reductive workup with sodium borohydride. The starting 8-lactams can be prepared via [2 + 2] cycloaddition of alkoxy ketenes and an azine and upon treatment with ozone at low temperature, yield the expected secondary ozonides (eq 59). Reduction of the ozonide leads to the corresponding N-nitroso intermediate, which is susceptible to fragmentation of the C4—N1 bond to give a zwitterion intermediate that rearranges to yield the product enol ethers. In the reaction sequence, fra 5- 8-lactams yield predominantly the E-enol ether while the d5- 8-lactams preferentially form the Z-configured enol ethers. 

Reactions of azines with ketenes 4,5-Dihydro-l,3-oxazin-6-ones from 2 ketene molecules... 

Thermal reaction of affenyf azines derived from propargylphosphonium salts with ketenes, isocyanates. CS2 or phthallc anhydride to form bi and Incyclic fused pyrazolo heterocycles... 

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