Regiodivergent Stereoselective Access to Fused Alkylideneazetidines

Following
recent advances in the generalization and simplification
of 2H-azetine synthesis, a regiodivergent approach
to fused 2- and 3-alkylideneazetines was designed via the intermediate
formation of unprecedented vinylazetine structures. Concise sequences
to the latter are described from which an expected unsaturated fused
ring system was isolated with very high yields and regio- and stereoselectivities
by [4 + 2] cycloadditions.