研究了目标2,3-二氢[1,3]恶唑并[3,2- a ]-吡啶鎓盐的合成过程中的缩合，烷基化和卤环化反应的顺序。已经揭示了碱性催化对丙二腈与乙酰丙酮反应的化学选择性的影响。在中性介质中，3-氰基-4,6-二甲基-2-吡啶酮形成的选择性增加。Et 3的存在另一方面，N导致副产物的形成。3-氰基-4,6-二甲基-2-吡啶酮的烯丙基化继续进行，形成区域异构的1-烯丙基-3-氰基-4,6-二甲基-2-吡啶酮和2-烯丙基-3-氰基-4,6 -二甲氧基吡啶的比例为3：1，而烯丙基衍生物与碘或溴的卤代环化反应则具有很高的化学选择性，可实际定量地产生2,3-二氢[1,3]恶唑并[3,2- a ]吡啶鎓盐的产率。
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Synthesis and halocyclization of 3-cyano-4,6-dimethyl-2-pyridone allyl derivatives
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.
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