Cycloaddition-modification-ring cleavage

Stmctural features of olefin cycloadducts (i.e., isoxazolines) were extended when regioselective 4-endo- and 3 -exo-deprotonations were discovered, with the broad range of ensuing reactions of these carbanions that are common with electrophiles (19-22, 26-28). Thus, sequences consisting of cycloaddition-modification-ring cleavage were utilized to build up complex structures (17, 20-23). 

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