Synthesis of Spirocyclic Amines by Using Dipolar Cycloadditions of Nitrones

Aliphatic ketones containing a chloride
and alkene were heated
with hydroxylamine to promote cascade, tandem condensation to oximes,
cyclization to nitrones, and 1,3-dipolar cycloaddition to tricyclic
isoxazolidines as single stereoisomers. Single regioisomers were obtained
when three atoms linked the ketone and dipolarophile to give five-membered
rings but mixtures resulted with four atoms in the tether unless a
terminal ester was located on the alkene. The N–O bond in the
products could be reduced to give spirocyclic amines and diamines.