非キレート配座規制を基盤とする含窒素天然物のキラル合成

Abstract

In this review our own work on the development of chiral approaches to nitrogenous natural products based on a methodology involving conformational control in the transition states under nonchelation conditions has been presented. On 1, 2-asymmetric induction in the reaction of achiral reagents at the diastereotopic faces of a prochiral C=X (X=C, N, O etc.) group adjacent to an asymmetric carbon atom, the increased π-facial selectivity is brought about by conformational fixation of the single bond between the asymmetric center and the prochiral reaction center. Apart from cyclic chelation control, the useful ways to achieve this is to utilize the conformational restraints imposed by Cram-Felkin-Anh mode of nucleophilic addition, inside alkoxy effect, and allylic 1, 3-strain. Employing these nonchelation methodologies for controlling the stereochemistry of acyclic systems, we have succeeded in the enantiopure preparation of nitrogenous natural products including alkaloids, azasugars, and antibiotics.