Synthesis and halocyclization of 3-cyano-4,6-dimethyl-2-pyridone allyl derivatives

Abstract

The sequence of condensation, alkylation, and halocyclization reactions during the synthesis of the target 2,3-dihydro[1,3]oxazolo[3,2-a]-pyridinium salts was investigated. The effect of basic catalysis on the chemoselectivity of the reaction of malononitrile with acetylacetone has been revealed. In neutral media, the selectivity of the formation of 3-cyano-4,6-dimethyl-2-pyridone increases. The presence of Et3N, on the other hand, leads to the formation of side products. Allylation of 3-cyano-4,6-dimethyl-2-pyridone proceeds with the formation of regioisomeric 1-allyl-3-cyano-4,6-dimethyl-2-pyridone and 2-allyl-3-cyano-4,6-dimethyloxypyridine in a 3:1 ratio, while the high chemoselectivity of halocyclization of allyl derivatives with iodine or bromine results in practically quantitative yields of 2,3-dihydro[1,3]oxazolo[3,2-a]pyridinium salts.