Examination of homo-[3 + 2]-dipolar cycloaddition: mechanistic insight into regio- and diastereoselectivity.
The reaction of 2,3-disubstituted-1,1-cyclopropanediesters with nitrones under Lewis acid conditions produces tetrahydro-1,2-oxazines in which the cis/trans relationship of the cyclopropanes is not conserved. Reacting nitrones with 2,3-cis-disubstituted cyclopropanes lead to 5,6-trans-oxazines, and 2,3-trans-disubstituted cyclopropanes lead to 5,6-cis-oxazines. This observed stereochemical inversion provides evidence for a stepwise annulation mechanism in the preparation of tetrahydro-1,2-oxazines.
Karadeolian
Avedis
A
Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada.
Kerr
Michael A
MA