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Due in large part to the utility of enantiomerically enriched alcohols and their selectively O-protected derivatives, considerable energy has been devoted to the search for efficient catalysts for the asymmetric hydrosilylation of ketones.[1] Very good enantioselectivities have been obtained for many aryl alkyl ketones, but for dialkyl ketones they are generally more modest. Seminal discoveries have resulted from these efforts, including the development of pybox, the first highly effective bis(oxazoline)-based ligand. [2, 3] During the past few years, we have been pursuing the design and development of new chiral ligands that are based on ™planar-chiral∫ heterocycles, [4] and for several metalcatalyzed processes we have demonstrated that this family of ligands can provide enantioselectivity superior to the best methods that had previously been reported. [5] Here we describe the synthesis of a new planar-chiral P,N ligand, and we establish its exceptional efficiency in rhodium-catalyzed asymmetric hydrosilylations of aryl alkyl ketones and dialkyl ketones [Eq. (1)].

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It has come to our attention that an oxygenated triterpenoid denoted saponaceolide A (see, e.g., De Bernardi, M.; Garlaschelli, L.; Toma, L. Vidari, G.; Vita-Finzi, P. Tetrahedron 1991, 47, 7109), while quite different in overall structure than mispyric acid, nonetheless has the same basic carbon skeleton. A biogenetic pathway essentially the same as the one proposed for mispyric acid has previously been proposed for saponaceolide A.We thank Prof. Giovanni Vidari for bringing this earlier work to our attention.

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Due in large part to the utility of enantiomerically enriched alcohols and their selectively O-protected derivatives, considerable energy has been devoted to the search for efficient catalysts for the asymmetric hydrosilylation of ketones.[1] Very good enantioselectivities have been obtained for many aryl alkyl ketones, but for dialkyl ketones they are generally more modest. Seminal discoveries have resulted from these efforts, including the development of pybox, the first highly effective bis(oxazoline)-based ligand. [2, 3] During the past few years, we have been pursuing the design and development of new chiral ligands that are based on ™planar-chiral∫ heterocycles, [4] and for several metalcatalyzed processes we have demonstrated that this family of ligands can provide enantioselectivity superior to the best methods that had previously been reported. [5] Here we describe the synthesis of a new planar-chiral P,N ligand, and we establish its exceptional efficiency in rhodium-catalyzed asymmetric hydrosilylations of aryl alkyl ketones and dialkyl ketones [Eq. (1)].

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