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Transannular Diels-Alder Reaction Catalyzed by Chiral Oxazaborolidine
E. P. Balskus, E. N. Jacobsen*
Harvard University, Cambridge, USA
22 November 2007 (online)
While catalytic, asymmetric intermolecular and intramolecular Diels-Alder reactions are well established, the present paper provides the first report of the corresponding transannular Diels-Alder (TADA) reaction. A survey of various Lewis and Brønsted acid catalysts revealed that oxazaborolidine 1 was the only catalyst able to promote cyclization of macrolactone 2 (n, m = 1). Subsequently, various-sized macrocycles containing α,β-unsaturated lactone or ketone dienophilic moieties were cyclized to furnish tricyclic endo products containing medium-to-large-sized rings in good to excellent diastereo- and enantioselectivities.