Three-Component Homo 3 + 2 Dipolar Cycloaddition. A Diversity-Oriented Synthesis of Tetrahydro-1,2-oxazines and FR900482 Skeletal Congeners

[reaction: see text] The reaction of nitrones, formed in situ by reaction of hydroxylamines with aldehydes, with 1,1-cyclopropanediesters results in the formation of tetrahydro-1,2-oxazines via a homo 3 + 2 dipolar cycloaddition. This three-component coupling allows for the formation of a diverse array of cycloadducts with excellent diastereoselectivity (>95%) and yields (66-96%). The procedure has been used in the two-step preparation of congeners of the FR900482 skeleton.