SYNTHETIC STUDIES OF HALICHONDRIN-B, AN ANTITUMOR POLYETHER MACROLIDEISOLATED FROM A MARINE SPONGE .5. A HIGHLY CONCISE AND EFFICIENT SYNTHESIS OF THE C-37-APPROXIMATE-TO-C-54 TRICYCLIC JKL-RING PART

A concise and efficient synthesis of C(37)similar to C-54 tricyclic JK L-ring unit (2) of halichondrin B (1) utilizing C-2-symmetric spiroket al derivative (5) as a synthetic key intermediate, easily provided fro m dimethyl L-(+)-tartrate, is reported.