Rhodium-catalysed asymmetric ring opening of oxabicyclic alkenes with heteroatom nucleophiles

We describe a new rhodium catalysed asymmetric ring opening (ARO) reaction of oxabenzonorbornadienes. This reaction produces a new carbon-oxygen bond via an intermolecular allylic displacement of the bridgehead oxygen with a wide variety of alcohols and phenols. This reaction occurs under neutral reaction conditions, and no activation of the alcohol nucleophile is required. It proceeds with very high regio- and diastereoselectivity (> 99:1), and excellent enantioselectivity (up to 99%ee). Symmetrical substitution patterns on the aromatic ring of the oxabenzonorbornadienes had no effect on the course of the reaction nor the enantioselectivity. The reaction produces an unusual stereochemical outcome for oxabicyclic ring openings since the trans rather than the cis product is formed. Very low catalyst loadings can be used, typically 0.25 mol% of the catalytically active rhodium species. (C) 2001 Elsevier Science B.V. All rights reserved.