Synthesis of β-hydroxy-α-haloesters through super silyl ester directed syn-selective aldol reaction

Neighboring Effect of Intramolecular Chlorine Atoms on Epoxide Opening Reaction by Chloride Anions

We investigated the diastereoselectivity of ring openings for chloro vinyl epoxides with various chlorination reagents. In the chlorinolysis reactions using vinyl epoxides having an allyl alcohol, inversion:retention ratios varied depending on the chloride sources. In limited cases, the increase in retention ratio was consistent with the intervention of chloronium ions. In contrast, all vinyl epoxides bearing an α,β-unsaturated ester gave only the inversion products. These results suggest the electron-withdrawing property suppressed the chloronium ions.

Total Synthesis of (-)-L-755,807: Establishment of Relative and Absolute Configurations

The first total synthesis of (-)-L-755,807 and its three stereoisomers was achieved by our Horner-Wadsworth-Emmons reaction for stereoselective formation of trisubstituted olefins, highly diastereoselective Darzens condensation to construct the epoxy-γ-lactam ring, and late-stage coupling of the ring and side-chain segments for efficient convergent synthesis. This synthesis shows that the originally proposed structure of natural (-)-L-755,807 was incorrect and establishes its relative and absolute configurations.