Amidation reactions, silver-mediated oxidation

The synthesis of the C29-C43 EF segment 479 is summarized in Scheme 68. Methylation of 467 under Prater s conditions stereoselectively afforded 2,3-anti compound 468 (dr = 5-8 1). After TES protection followed by thioester reduction, aldol reaction of the resulting aldehyde with thioketene acetal afforded a-alcohol 469 under Felkin-Anh selectivity. TES deprotection and silver-mediated lactonization followed by TES protection and lactone reduction gave lactol 470. Dehydration, debenzylation, and oxidation furnished aldehyde 471, which was transformed to benzotriazolyl amide 472. 

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