An Approach to 6-Oxygenated Shikimic Acid Derivatives by Photolysis of the Pyruvate Ester of Dimethyl Epoxychorismate

Abstract

We report an unusual rearrangenaent of a synthetic epoxychorismic acid derivative which provides access to the 6-substituted shikimic acid framework. Photolysis of the pyruvate ester of dimethyl epoxychorismate triggered an intramolecular Paterno-Buchi photocyclization of the enol pyruvate alkene and the ketone group of the pyruvate ester, leading to a 2,2,3,3-tetrasubstituted oxetane ring. Upon standing for 1 week in CDCl 3 or in the presence of CF 3 CO 2 D, the primary photoproduct under- went a slow epoxide-opening reaction with participation by the oxetane- substituted carbomethoxy group to form an unusual fused tetracyclic lactone. The chemistry described here suggests at least one plausible pathway, with appropriate stereoelectronic constraints, by which oxi- dation of shikimic acid at C6 might be achieved