X = Y - ZH systems as potential 1,3-dipoles part 35. Generation of nitrones from oximes. Class 3 processes. Tandem intramolecular Michael addition (1,3-azaprotio cyclotransfer) - Intermolecular 1,3-dipolar cycloaddition reactions

Article abstract of DOI:10.1016/S0040-4020(01)89883-5

Aldoximes and ketoximes possessing γ- or δ-alkenyl substituents undergo thermal conversion to 5-and 6- membered cyclic nitrones via a 1,3-azaprotio cyclotransfer, a 2n + 2oσ + 2π concerted process, rather than a Michael addition. The reactions can be performed as a tandem nitrone formation-cycloaddition sequence or, if required, the intermediate nitrones can be isolated. The cycloadditions usually proceed via an exo-transition state and show both regio- and diastereofacial-specificity. Preliminary attempts at chiral induction via a menthyl auxiliary are reported.