Access to chiral 3-benzylchromanones and 2,6-disubstituted cyclohexanones via Rh-catalyzed chemo- and enantioselective hydrogenation of arylidene chromanones/cyclohexanones

Abstract

A highly chemo- and enantioselective hydrogenation of arylidene chromanones/cyclohexanones catalyzed by the Rh-f-spiroPhos complex has been developed, providing a series of chiral 3-benzylchromanones in high yields (93–99%) with excellent enantioselectivities (up to 98% ee) and achieving high turnover numbers (TON = 2000). Furthermore, an efficient desymmetrizing enantioselective hydrogenation of 3,5-dibenzylidene chromanones and 2,6-dibenzylidene cyclohexanones has also been realized, delivering chiral dibenzyl chromanones/cyclohexanones with excellent chemo-, diastereo- and enantioselectivities (up to >20 : 1 trans : cis, >99% ee). This methodology provides straightforward and mild access to the asymmetric synthesis of α-chiral ketones.