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

Abstract

We report a n unusual rearrangement 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 a n intramolecular Paterno-Buchi photocyclization of the enol pyruvate alkene and the ketone group of the pyruvate ester, leading to a 2,2,3,34etrasubstituted oxetane ring. Upon standing for 1 week in CDC4 or in the presence of CF~COZD, the primary photoproduct underwent a slow epoxide-opening reaction with participation by the oxetane-substituted carbomethoxy group to form a n unusual fused tetracyclic lactone. The chemistry described here suggests a t least one plausible pathway, with appropriate stereoelectronic constraints, by which oxidation of shikimic acid a t C6 might be achieved.

Intramolecular 2 + 2 Cycloaddition in a Baccatin. From a Tetracyclic to a Hexacyclic Molecule

“…Irradiation of solutions of 9 with light of only moderate intensity rapidly accelerated the conversion into 10 , consistent with formulation of the reaction as a 2 + 2 or Paterno−Buchi cyclization − …”