合成路线1

Synthesis of intermediate (L): The condensation of aldehyde intermediate (XLIII) with iodovinyl intermediate (XXXIII) by means of NiCl2/CrCl2 bispyridinyl ligand in THF, followed by a treatment with DMP, gives the adduct (XLIV), which is treated with PPTS to yield the bis spiroketal (XLV) with undesired configuration at the new stereocenter. The treatment of (XLV) with HF/pyridine in acetonitrile gives rise to a desilylation of the TBDMS group with concomitant isomerization of the new stereocenter yielding a separable mixture of two diastereomers (XLVI) and (XLVII). Compound (XLVII) has the desired configuration, and (XLVI) can be recovered by isomerizing it again to the starting diastereomeric mixture. The silylation of (XLVII) with TBDMS-OTf, followed by selective monodesilylation of the primary OH group with HF/pyridine in THF, gives the ethanol derivative (XLVIII), which is oxidized with tetrapropylammonium perruthenate (TPAP) and NaClO2 and silylated with TBDPSCl to yield the silyl ester (XLIX). Finally, this compound is selectively deprotected with DDQ and oxidized with DMP to afford the desired aldehydic intermediate (L).