An aldol approach to a building block corresponding to the C21–C26-part of FK506

Starting from D-tartrate 2 , the chiral aldehyde 10 was prepared in 8 steps. Key steps include the reductive opening of the p-methoxybenzyl acetal 4 and the elongation of the aldehyde 7 via Wittig and hydroboration reaction providing the alcohol 9 . Subsequent Evans aldol reaction provided compound 12 which corresponds to the C21–C26 part of the immunosuppressive FK506.