TANDEM 1,3-DIPOLAR CYCLOADDITION AND ELECTROPHILIC CYCLIZATION REACTIONS - CYCLIC ETHER SUBUNITS OF POLYETHER ANTIBIOTICS FROM UNSATURATED ISOXAZOLINES

A new strategy for the construction of polyether antibiotic substructural units [spiroketals (I), tetrahydrofurans (II), and tetrahydropyrans (III)] consisting of bis-addition of an oxygen nucleophile across an a,co-diene moiety (i.e., IV) is described. The method exploits a tandem 1,3-dipolar cycloaddition/electrophilic cyclization sequence that proceeds via the intermediacy of an isoxazoline. Experiments presented illustrate the versatility of this strategy, which provides a unique exploit of the control elements operative in dipolar cycloaddition and electrophilic cyclization chemistry. © 1990, American Chemical Society. All rights reserved.