SYNTHETIC APPROACH TO TETRAHYDROFURAN UNITS AND FIVE-MEMBERED RING LACTONES FUSED TO HEXOPYRANOSIDES ^*

Abstract

A stereoselective synthesis of the miharamycin sugar moiety epimer at C-3′ was accomplished in high yield starting from an appropriate (Z)-Wittig product, synthesized by Wittig reaction of a 4,6-O-benzylidene protected hexopyranosid-3-ulose with [(ethoxycarbonyl)methylene]triphenylphosphorane followed by iodine promoted isomerisation of the (E)-Wittig product formed. Reduction of the (Z)-isomer obtained in quantitative yield, cyclisation and dihydroxylation with osmium tetroxide, gave the target molecule containing a cis-fused tetrahydrofuran ring in its structure. Synthesis of five-membered rings trans-fused to the hexopyranosidic units succeeded via two different synthetic pathways. Stereoselective Reformatsky reaction of a 2,6-di-O-pivaloyl protected hexopyranosid-3-ulose, followed by cyclisation with dimethylzinc gave a 3,4-trans-fused lactone. The approach using the reaction of 2,3-and 3,4-epoxides with the dianion of phenylselenoacetic acid led to low yield but novel phenylseleno derivatives of trans-fused five-membered rings, namely a phenylselenolactone 2,3-trans-fused to a 4,6-O-benzylidenehexopyranoside and a phenylselenolactenol 3,4-trans-fused to a 6-O-pivaloyl-hexopyranoside.

^*Dedicated to the 60th birthday of Prof. Joachim Thiem.

ACKNOWLEDGMENTS

The authors are grateful to the Junta Nacional de Investigação Científica e Tecnológica for a research grant and Eng. Fernando Matos for running some NMR spectra.

Notes

^*Dedicated to the 60th birthday of Prof. Joachim Thiem.