Efficient Entry to Highly Functionalized β-Lactams by Regio- and Stereoselective 1,3-Dipolar Cycloaddition Reaction of 2-Azetidinone-Tethered Nitrones. Synthetic Applications

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Racemic as well as optically pure 2-azetidinone-tethered nitrones, both cyclic and acyclic, were smoothly prepared from 4-oxoazetidine-2-carbaldehydes. The regio- and diastereoselectivities of the intermolecular 1,3-dipolar cycloaddition reactions of 2-azetidinone-tethered nitrones with substituted alkenes and alkynes were investigated. 2-Azetidinone-tethered nitrones on reacting with various dipolarophiles yielded isoxazolinyl-, isoxazolidinyl-, or fused polycyclic-beta-lactams, exhibiting good regio- and facial stereoselectivity in the most of the cases. In addition, some interesting transformations of these cycloadducts were performed, yielding aziridinyl beta-lactams or functionalized beta-alkoxycarbonyl gamma-lactams (derivatives of the aza analogue of paraconic acid).