Synthesis and X-ray crystal structure of (-)-calicheamicinone

Diels-Alder reaction between ketene acetal 3 and the beta-nitroacrylate est er 12 of (-)-8-phenylmenthol gave optically pure ketone 17. This substance was modified in such a way as to remove the chiral auxiliary and afford the epimeric silyl ethers 20M and 20m. Following procedures worked out using r acemic materials, both 20M and 20m were converted into optically pure (-)-c alicheamicinone (1). This is a crystalline substance, and an X-ray structur e determination was carried out. (C) 1999 Elsevier Science Ltd. Ail rights reserved.