Diastereoselective Synthesis of the Key Intermediate of the BO-2727 Side Chain.

Abstract The key intermediate of the BO-2727 side chain 3 was prepared diastereoselectively by two alternative methods: via the aldol reaction of (2S,4R)-N-Boc- tert -butyldimethylsilyloxyprolinal 5 with in-situ -generated ketene acetal 9 in the presence of TiCl 4 (95% de) and via the catalytic hydrogenation of β-keto amide 6i using (S)-BINAP-Ru as a catalyst (98% de).