Characteristics of the Intermediates in the Cyclization Reactions of Heterocycle-fused[l,4]oxazine Derivatives:Stepwise versus Concerted

摘要

The reaction mechanisms for the cyclizations of N-methyl-2-(2-chloropyridin-3-yloxy)acetamide to 1-methyl-pyrido[3,2-b][l,4]oxazin-2-one and l-methyl-pyrido[2,3-b][l,4]oxazin-2-one were investigated using ab initio Hartree-Fock,second-order Moller-Plesset perturbation,single point coupled cluster with both single and double substitution,and density functional theory methods.The 5-membered spiro intermediate (2) is optimized from the cyclization of the acyclic reactants through the proton-transfer reaction,and this intermediate proceeds continuously to the 6-membered intermediate through either a stepwise or a concerted reaction.In the stepwise reaction,an N-bridge-type intermediate as a stable structure is optimized,whereas,in the concerted reaction,the O-bridge-type intermediate is not optimized.