Asymmetric Synthesis of Loganin. Stereospecific Formation of (1R,2R)- and (1S,2S)-2-Methyl-3-cyclopenten-1-ol And (2R)- and (2S)-2-Methylcyclopentanone

Abstract

A short asymmetrically induced synthesis of loganin pentaacetate (6) has been completed. 5-Methylcy-clopentadiene (7) underwent a highly selective reaction with (+)-di-3-pinanylborane to yield (1R,2R)-2-methyl-3-cyclopenten-l-ol (8a) of 95% minimum optical purity. (-)-Di-3-pinanylborane gave (1S,2S)-2-methyl-3-cyclopenten-l-ol (8b) of equivalent optical purity. The absolute configurations of alcohols 8a and 8b were determined by their conversion into the previously unknown (2R)- and (2S)-2-methylcyclopentanones (12a and 12b) and measuring the ORD and CD spectra of these ketones. The 1R,2R alcohol 8a afforded the optically active methanesulfonate 10 which was converted into the 1S,2R acetate 2 with tetraethylammonium acetate. Irradiation of a 10:1 mixture of acetate 2 and methyl diformylacetate (3) gave the desired loganin aglucone derivative 5 regioselectively. Treatment of 5 with 2,3,4,6-tetra-O-acetyl-β-D-gl ucose and boron trifluoride afforded loganin pentaacetate (6) which has been converted to loganin (1). © 1973, American Chemical Society. All rights reserved.