# Synthesis of 3‑C‑Methyl‑d‑Mannopyranoside Derivatives Functionalized at the 3‑Position

## TL;DR

This paper presents new methods for synthesizing and studying 3-C-methyl-d-mannopyranoside derivatives, focusing on their structural variations and stereoselectivity.

## Contribution

The paper introduces alternative syntheses and observations of stereoselectivity reversal using different reagents in sugar derivative reactions.

## Key findings

- Alternative syntheses of 4,6-O-benzylidene-protected 3-C-methylmannopyranosyl donors and their 3-O-benzoates were developed.
- A reversible migration of a 2-O-silyl derivative was observed during attempted esterification.
- The Corey–Chaykovky reaction showed reversed stereoselectivity based on the reagent used, affecting the isomer produced.

## Abstract

3-C-Methyl-d-mannopyranose
is a rare
branched sugar whose derivatives also serve as precursors to the more
common d-evalose (6-deoxy-3-C-methyl-d-mannose) and, after esterification at O3, as probes for the
study of the mechanism of the stereodirecting effect of esters at
the 3-position in mannopyranosylation reactions. We describe alternative
syntheses of 4,6-O-benzylidene-protected 3-C-methylmannopyranosyl donors and their 3-O-benzoates and an interesting, reversible migration of a 2-O-silyl derivative on the attempted esterification at O3.
We also describe the reversal of stereoselectivity on application
of the Corey–Chaykovsky reaction to a 3-keto sugar based on
a 4,6-O-benzylidene-protected α-mannopyranoside:
the trimethylsulfonium iodide-derived ylid favored axial attack leading
to the desired mannoisomer, whereas the more bulky trimethylsulfoxonium
iodide-derived ylid gave the altro isomer of the resulting spiroepoxide
as a consequence of preferential equatorial attack.