合成路线1

The synthesis of the dihydropyranyl acetaldehyde intermediate (XVII) has been obtained as follows: The reduction of the pentanedioic acid monoethyl ester (I) with BH3 gives the hydroxyester (II), which is oxidized with DMP to yield the aldehyde (III). The reaction of (III) with the chiral borane (IV) affords the 5-hydroxyoctenoic ester (V), which is treated with dimethylamine to provide the corresponding amide (VI). The reaction of (VI) with propenal diethylacetal (VII) gives ether (VIII), which is submitted to a ring closing metathesis reaction catalyzed by a Ru catalyst to yield the dihydropyran derivative (IX). The reaction of (IX) with tert-butyldimethylsilyloxy ethylene (X) catalyzed by LiClO4 affords the dihydropyranyl acetaldehyde (XI), which is reduced with NaBH4 and protected with Tes-Cl to provide the butyramide (XII). The reaction of (XII) with MeLi gives the pentanone (XIII), which is treated with Ph-NTf2 and KHMDS to yield the enol triflate (XIV). The reaction of (XIV) with Tms-CH2-MgCl affords the methylene derivative (XV), which is selectively desilylated with K2CO3 to provide the dihdyropyranyl ethanol compound (XVI). Finally, this compound is oxidized with DMP to obtain the target dihydropyranyl acetaldehyde intermediate (XVII).