Concise Synthesis of a New Chiral Cyclopentenone Building Block for Prostaglandins and their Derivatives

Abstract

(4R,5R)‐4,5‐O‐isopropylidene‐2‐(dimethoxyphosphoryl)cyclopen‐2‐enone was obtained in enantiomerically pure form in four steps starting from commercially available 2,3‐O‐isopropylidene‐D‐erythronolactone. The key steps involved are diastereoselective lactone ring opening leading in a one‐pot procedure to the ε‐silyloxy Weinreb‐type amide, and the cyclopentenone ring formation by the rhodium catalyzed carbenoid cyclization of the corresponding ε‐silyloxy‐α‐diazo‐β‐ketophosphonate followed by the elimination of tert‐butyldimethylsilanol. During the synthetic study on the construction of the cyclopentanone ring by the intramolecular nucleophilic substitution reaction of an anion generated from ε‐bromo‐β‐ketophosphonate, the formation of cyclopropane derivative was observed. This stereochemical outcome was rationalized using quantum chemical calculations.