Synthesis and X-ray Analysis of Dihydro-1,2,4,5-trioxazine. Evidence of a Steowise Mechanism for the Cycloaddition of Carbonyl Oxides with Nitrones

Article abstract of DOI:10.1021/jo00034a018

Carbonyl oxides, derived by ozonolysis of vinyl ethers, readily undergo <3 + 3> cycloaddition reactions with nitrones affording dihydro-1,2,4,5-trioxazines in fair to excellent yield.The structures of dihydro-3,5,6-triphenyl-1,2,4,5-trioxazine (5f) and dihydro-3-cyclohexyl-5-methyl-6,6-diphenyl-1,2,4,5-trioxazine (5t) were unambiguously determined by X-ray analysis.Ozonolysis of 1-cyclohexyl-2-methoxyethene in the presence of either (E)- or (Z)-α-(4-methylphenyl)-α-phenyl-N-methylnitrone gave a 1:1 mixture of two stereoisomeric cycloadducts.This result, in conjunction with the structure of the relevant 5t, suggests that the <3 + 3> cycloaddition proceeds by a stepwise mechanism.