ZIRCONOCENE-CATALYZED EPOXY ESTER ORTHO ESTER REARRANGEMENT - A NEW METHOD FOR THE PROTECTION OF POLYFUNCTIONALIZED CARBOXYLIC ACIDS AND THE ASYMMETRIC SYNTHESIS OF ORTHO ESTERS

摘要

In situ prepared Cp-2(Cl)Zr+ catalyzes the formation of ortho esters from epoxy esters. Acid-sensitive alpha-amino and alpha-hydroxy acid derivatives are converted in high yield to 2,7,8-trioxabicyclo[3.2.1]octanes (ABO-esters) using this protocol. This strategy is complementary to the OBO-ester technology, and orthogonal methods for the deprotection of ABO- and OBO-esters have been developed. The syntheses of the mushroom components (S)-gamma-hydroxyleucine lactone and (S)-alpha-vinylglycine underline the value of ABO-ester protective group strategy. Using chiral epoxy alcohol derivatives, the first convenient and general asymmetric synthesis of bicyclic ortho esters has been achieved. (C) 1997 Elsevier Science Ltd. [References: 44]