Stereoselective allylation of α-hydroxy aldimines and its application to the formal synthesis of (−)-β-conhydrine

Recent advances in the total synthesis of polyhydroxylated alkaloids via chiral oxazines

This review summarizes recently established methodologies developed for the enantioselective and diastereoselective synthesis of chiral 1,3-oxazines. These compounds are of interest as advanced synthetic intermediates in the total synthesis of structurally complex and biologically active polyhydroxylated alkaloids such as (+)-1-deoxynojirimycin, (-)-anisomycin, (+)-castanospermine, (+)-casuarine, (-)-conduramine F-1, (-)-sphingofungin B, Neu5Ac methyl ester, and other natural products. The devised synthetic approach aims to offer a direct, efficient, and adaptable method for obtaining both pure enantiomers and pure diastereomers. It revolves around utilizing chiral building blocks like syn,syn-, syn,syn,anti-, syn,anti-, syn,anti,syn-, anti,syn-, anti,syn,syn-, and anti,syn,anti-oxazines. By integrating oxazine chemistry with established and innovative transformations, this approach enabled the synthesis of 30 polyhydroxylated amines across various studies conducted between 2007 and 2022.

Crystallization-Induced Diastereomer Transformation of α-Bromo α'-Sulfinyl Ketones. Diastereodivergent Synthesis of (+)-α-Conhydrine and (-)-β-Conhydrine

Crystallization-Induced Diastereomer Transformation (CIDT) of α-bromo-α'-(R)-sulfinylketones is reported. This process provides not readily accessible enantiopure stereolabile α-bromoketones, which after diastereoselective carbonyl group reduction lead to the corresponding highly value-added anti and syn-bromohydrins with excellent diastereoselectivities. As an application, a diastereodivergent synthesis of enantiopure hemlock alkaloid (+)-α-conhydrine and its diastereomer (-)-β-conhydrine is also described.

Reactions of Allylmagnesium Reagents with Carbonyl Compounds and Compounds with C═N Double Bonds: Their Diastereoselectivities Generally Cannot Be Analyzed Using the Felkin-Anh and Chelation-Control Models

This review describes the additions of allylmagnesium reagents to carbonyl compounds and to imines, focusing on the differences in reactivity between allylmagnesium halides and other Grignard reagents. In many cases, allylmagnesium reagents either react with low stereoselectivity when other Grignard reagents react with high selectivity, or allylmagnesium reagents react with the opposite stereoselectivity. This review collects hundreds of examples, discusses the origins of stereoselectivities or the lack of stereoselectivity, and evaluates why selectivity may not occur and when it will likely occur.