合成路线1

The C1-C6 building block (V) (segment A) can be obtained as follows. Protection of (–)-pantolactone (X) as the tetrahydropyranyl ether (XI) using dihydropyran and pyridinium tosylate, followed by reduction of the lactone ring with DIBAL in cold toluene, gives the lactol (XII). Subsequent Wittig reaction of the cyclic hemiacetal (XII) with methylene triphenylphosphorane affords the hydroxy olefin (XIII), which is protected as the benzyl ether (XIV) by treatment with benzyl bromide and potassium tert-butoxide. Hydroboration of olefin (XIV) followed by quenching with alkaline H2O2 provides the primary alcohol (XV) as the major isomer, which is converted to the acetonide (XVI) by treatment with 2,2-dimethoxypropane and p-toluenesulfonic acid. After catalytic hydrogenolysis of the benzyl ether (XVI), the deprotected alcohol (XVII) is oxidized to aldehyde (XVIII) under Swern conditions. Then, addition of 3-butenylmagnesium bromide (XIX) to the aldehyde (XVIII) provides alcohol (XX), which is oxidized to the target ketone (V) by treatment with N-methylmorpholine N-oxide and a catalytic amount of tetrapropylammonium perruthenate (3). Scheme 2.