# Stereoselective Synthesis of C‑Glycosylated Pyrrolizidines through Nitrone Cycloadditions

## TL;DR

This paper presents a new method for creating complex sugar-like molecules with potential biological applications using a selective chemical reaction.

## Contribution

A concise and stereoselective synthesis of C-glycosylated pyrrolizidines via nitrone cycloadditions is developed.

## Key findings

- Five novel C-glycosylated pyrrolizidines were synthesized using 1,3-dipolar cycloadditions of nitrones with E-alkenes.
- The reactions showed predictable anti-selectivity, leading to isoxazolidine intermediates.
- Stereochemical assignments were confirmed using NOE analyses.

## Abstract

Polyhydroxylated alkaloids, among which iminosugars represent
a
prominent subclass, are a structurally diverse family of carbohydrate
mimics with significant biological activity. Herein, we report a concise
and stereoselective synthesis of five novel C-glycosylated pyrrolizidines
(15–19) related to casuarine and
hyacinthacines, achieved through 1,3-dipolar cycloadditions of nitrones
with E-alkenes. The reactions of nitrone 21 with fructose-derived α,β-unsaturated ester 20a and ketone 20b proceeded with predictable anti-selectivity,
affording isoxazolidine intermediates that were transformed into pyrrolizidines
via reductive N–O cleavage and subsequent ring closure. Careful
stereochemical assignments were established by NOE analyses.