Unexpected Course of [2+3] Cycloaddition of 2-nitropropene to (Z)-C,N-diphenylnitrone

The [2+3] cycloaddition of 2-nitropropene to (Z)-C,N-diphenylnitrone leads to 3,4-trans-2,3-diphenyl-4-nitro-4- methyl- and 3,5-trans-2,3-diphenyl-5-nitro-5-methylisoxazolidines as primary reaction products. This, however, is not the only pathway of 2-nitropropene conversion. In the reaction conditions, the nitroalkene also undergoes isomerisation and the resulting trans- and cis-1-nitropropenes yield respective stereoisomeric 2,3-diphenyl-4-nitro-5-methylisoxazolidines in the reaction with (Z)-C,N-diphenylnitrone.