The C15-C16 bond of FK-506 was formed via sulfone anion coupling follo
wed by chelation controlled reduction of the C15 ketone. Efficient met
hylation of the CIS-OH was accomplished by a combination of Me3OBF4-4
Angstrom molecular sieves in the presence of Proton Sponge((R)). A pro
cedure was developed to avoid epimerization al the C2 position of the
pipecolinate section during alkaline hydrolysis. A reductive fragmenta
tion of the C21-C24 [6,6]-spiroketal iodide using active Zn/Ag-graphit
e delivered the alpha'-allyl aldol section. The C9-C10 [5,6]-spiroketa
l acetonide was de-blocked via a novel beta-elimination, using a combi
nation of LiHMDS-Mg(HMDS)(2) in HMPA-DME (1:1), to afford an enediol a
cetal, which was oxidized with dimethyl dioxirane to generate the C8-C
10 alpha, beta- diketoamide acetal function. Final desilylations compl
eted the total synthesis of FK-506. (C) 1997 Elsevier Science Ltd.