Total synthesis and structure determination of plakortones

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Total synthesis of plakortone C and F was investigated.After alkylation of the propionate of Evans' chiral auxiliary and removal of the auxiliary, the carboxylic acid was transformed to the corresponding dimethyl amide, which was subjected to iodolactonization. The lactone, obtained diastereoselctively, was reduced to the diol, whose primary alcohol was protected as a trityl ether. The ketone derived in few steps as a precursor of the alkylidenecarbene was reacted with lithiotrimethylsilyldiazomethane to give a dihydrofuran. Allylic oxidation, followed by DIBAL reduction gave a lactol, which was treated with Ph_3CHCO_2Bn. The resulting saturated ester was a mixture of diastereomers, which were separable and each epimers could be epimerized with DBU.Hydrolysis of the ester, followed by iodolactonization and subsequent radical reduction afforded lactone aldehyde with the desired core part. After one carbon elongation, the aldehyde was subjected Wittig reaction to give αβ-unsaturated ester. The ester and lactone were reduced with DIBAL to lactol alcohol. The lactol was protected and the alcohol was oxididized to aldehyde, which was exposed to the enatioselective ethylation. Elimination and Claisen rearrangement of ortho-acetate of the alcohol gave the ester which was reduced to the hydrocarbon. Oxidation of the lactol part produced the final compound. The NMR spectra of the synthetic compound and, those of the natural one were not identical, therein, the natural product must be its diastereomer. The synthesis of the natural product will be accomplished in the similar way as the mute established in this investigation.