Six Ring Nitrogen Systems

Six Ring Nitrogen Systems.—ReducedPyridines. A -Substituted-l,2-dihydropyridines are of interest since they are implicated in indole-alkaloid biosynthesis. One of the few accessible derivatives is the carbamate (209), which on photolysis gives the 2-azabicyclo[2,2,0]hex-5-ene ester (210). Conditions for the conversion of the latter into the amine (211) have now been found, and several alkylations of this compound have been carried out thermolysis of these compounds has given jV-substituted 

2- dihydropyridines. ° Thermolysis of allenic amidines gave high yields of 

A useful synthesis of 2-piperidones from 3-substituted butyric esters, aldehydes, and amines in acetic acid has been reported. Yields vary, and the reactions are best 

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Fused Five and Six Ring Nitrogen Systems.—The acid catalysed reactions of alkyli-dene bisurethanes with conjugated dienes gave various azacyclic and azabicyclic molecules formed by 1,4 (or 1,6)-addition to the conjugated system by the acylimine (241). > In new work the first example of a formal 1,3-cycIoaddition during the reaction of (241) with dienes has been observed (Scheme 107). 

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