合成路线1

The silylation of the acetonide (XVIII) with Tms-Cl and LDA in THF gives dienolate (XIX), which is enantioselectively condensed with acrolein (XX) by means of Carreira's Ti catalyst in ethyl ether to yield the chiral allyl alcohol (XXI). The reaction of (XXI), N,O-dimethylhydroxylamine (XXII) and Me2AlCl affords the amide (XXIII), which is selectively reduced with Me4NBH(OAc)3 in HOAc/acetonitrile to provide the dihydroxyamide (XXIV). The silylation of the OH groups of (XXIV) with Tbdms-Cl and imidazole gives the disilylated compound (XXV), which is submitted to a Grignard reaction with vinylmagnesium bromide (XXVI) in THF to yield the vinyl ketone (XXVII). The Michael addition reaction with Ph2P(O)-Li and simultaneous triflation with (XXVIII) in THF affords the enol triflate (XXIX), which is cyclized by means of Pd(OAc)2, PPh3 and TEA in THF to provide the phosphorane (XXXa-b) as an inseparable mixture of the (Z)- and (E)-isomers. Finally, this mixture is submitted to photochemical isomerization with a medium-pressure UV mercury lamp in the presence of 9-fluorenone, furnishing the target intermediate, the (Z)-isomer (X) with a 95 % yield.