Highly Active Rhodium Catalyst with Electron-Poor Diphosphine Enables Efficient Synthesis of Chiral 4-Aryl-δ-lactones

Abstract

Chiral 4-aryl--lactones could be synthesized efficiently with high enantioselectivity through asymmetric 1,4-addition of arylboronic acid to α,β-unsaturated lactones using Rh catalyst including electron-poor diphosphine (MeO-F 12 -BIPHEP) at room temperature for 1 h.In particular, our catalytic system proved to be applicable to relatively large coumarin analogues, giving optically pure 4-phenylchroman-2-one analogues in a short time.Since Akira Suzuki and Norio Miyaura reported on the Suzuki-Miyaura coupling reaction in 1979, 1 researchers have utilized arylboronic acids for metal catalyzed cross-coupling reactions. 2Furthermore, the utility of arylboronic acids has been further enhanced by the development of the rhodium catalyzed asymmetric 1,4-addition of arylboronic acid to an α,β-unsaturated ketone. 3Using these reactions, chiral 4-substituted--lactones such as 4-phenyltetrahydro-2H-pyran-2-one (2) can also be synthesized from the α,β-unsaturated lactone, 5,6-dihydro-2H-pyran-2-one (1).The reactivity of 1 was equal to or less than that of 2-cyclohexenone (Scheme 1). 4 The reaction usually requires 3 -5 mol% Rh catalyst and a relatively higher reaction temperature (30 -100 °C).In addition, the reaction at room temperature or with less catalyst loading required a longer reaction time.In contrast, highly active rhodium catalysts for the reaction of 1 even at room temperature were developed in 2008. 5Here, 1 or 2 mol% Rh catalysts with chiral diene ligand obtained (R)-2a in a high yield with high enantioselectivity at room temperature for 3 or 1 h, respectively.Recently, we have developed a new type of electron-poor MeO-F 12 -BIPHEP ligand, which highly accelerates the rhodium-catalyzed 1,4-addition (Scheme 1). 6The catalytic system enabled