Total synthesis of patulolide C and its homo-, nor, and iso analogs
摘要:
The stereospecific total synthesis of the naturally occurring macrolide patulolide C 19Eb as well as its iso, nor, and homo analogs is described by applying the photoinduced rearrangement of enantiomerically pure epoxy diazomethyl ketones 14 to gamma-hydroxy alpha,beta-unsaturated esters 15 as the key step. The required epoxy diazomethyl ketones 14 are obtained by a Sharpless epoxidation of an appropriate allylic alcohol, followed by ruthenium tetraoxide oxidation to an oxiranecarboxylic acid, conversion into a mixed anhydride, and treatment with diazomethane. Macrolide 19Zb, which is a geometrical isomer of 19Eb, turned out to be a diastereomer of natural macrolide isopatulolide C, which implies the 4R,11R configuration for this natural material. X-ray diffraction analyses of 19Ea and 19Eb show that there is a considerable difference in spatial arrangement; particularly, the different torsion angles between the carbonyl and olefinic bonds are note worthy. The conformational behavior of these macrolides is also deduced from the NMR and UV spectra.
Total synthesis of patulolide C and its homo-, nor, and iso analogs
摘要:
The stereospecific total synthesis of the naturally occurring macrolide patulolide C 19Eb as well as its iso, nor, and homo analogs is described by applying the photoinduced rearrangement of enantiomerically pure epoxy diazomethyl ketones 14 to gamma-hydroxy alpha,beta-unsaturated esters 15 as the key step. The required epoxy diazomethyl ketones 14 are obtained by a Sharpless epoxidation of an appropriate allylic alcohol, followed by ruthenium tetraoxide oxidation to an oxiranecarboxylic acid, conversion into a mixed anhydride, and treatment with diazomethane. Macrolide 19Zb, which is a geometrical isomer of 19Eb, turned out to be a diastereomer of natural macrolide isopatulolide C, which implies the 4R,11R configuration for this natural material. X-ray diffraction analyses of 19Ea and 19Eb show that there is a considerable difference in spatial arrangement; particularly, the different torsion angles between the carbonyl and olefinic bonds are note worthy. The conformational behavior of these macrolides is also deduced from the NMR and UV spectra.
α,β-unsaturated esters is achieved, involving successively the Sharpless epoxidation of allylicalcohols, oxidation to glycidic acids, conversion into α,β-epoxy diazomethyl ketones, and irradiation in ethanol at 300 nm. Intermediates in the photo-induced rearrangement are epoxy ketenes, which undergo ethanolysis with simultaneous opening of the epoxide, preferably via a transition state involving the