The catalytic insertion reaction into O-H bond with a-diazocarbonyl compounds via a metal-carbenoid intermediate is a very useful organic transformation for the synthesis of oxygen-containing compounds.1-3) Remarkable advances, including enantioselective insertion, have been made in catalytic C-H insertions with a-diazocarbonyl compounds using Rh(II) complexes. [4][5][6][7][8][9] However, only limited success has been achieved for asymmetric insertions into O-H bond. 2,[10][11][12] Recently, Fu and Zhou independently reported asymmetric insertion reactions into alcoholic, 13) phenolic 14) and aquatic 15) O-H bonds with a-diazoacetate using chiral Cu(I) complexes. In contrast, chiral Rh(II) complexes gave poor enantioselectivity (8% ee) in the O-H insertion reaction, 11) while they have given remarkable results in the C-H insertion reaction. Since Rh(II) complexes are unique and powerful catalysts in the insertion reaction, we attempted to apply them to the enantioselective O-H insertion reaction.Recently, Liang et al. conducted a physicochemical approach to O-H insertion reactions using density functional theory (DFT). 10) They concluded that Rh(II) complex does not have enough affinity to the oxonium ylide intermediate to form firmly fixed stereocenter around the metal. Hence, we sought to design a novel approach to the enantioselective O-H insertion reaction catalyzed by Rh(II) complexes, independent of its own chirality. It is of interest that chiral amine additives expressed its own chirality on metal mediated epoxidation reaction using achiral Mn-salen complex. 16)Accordingly, we envisaged that an intermolecular O-H insertion of a-aryldiazoacetate and water should produce a mandelate in an enantioselective manner using cinchona alkaloids and Rh(II) complexes. Using this method, we now report that a combination of quinine (1) or quinidine (2) and dirhodium(II) tetra(triphenylacetate), Rh 2 (TPA) 4 , in the O-H insertion provides mandelate as the sole product in up to 50% ee.In our initial studies, we explored the intermolecular O-H insertion of methyl phenydiazoacetate in dichloromethane using 1 mol% of Rh 2 (TPA) 4 17,18) and 2 mol% of quinine (1) (Table 1, entry 1). [19][20][21][22] As expected, the reaction proceeded smoothly at 23°C to completion within 4 h, giving methyl mandelate in 82% yield. The enantioselectivity in this reaction was 38% ee, as determined by HPLC (Daicel Chiralcel OD-H). The preferred absolute stereochemistry was (S), which was established by comparing the sign of the optical rotation with the literature value.23) It is worth noting that enantioselectivity for a particular product was provided by the cinchona alkaloids, not by the rhodium catalyst. The enantiomeric induction in this system may be due to the formation of a chiral complex between rhodium-carbenenoid and cinchona alkaoid. To rule out the possibility that the reaction was catalyzed by quinine (1), we performed the reaction under identical conditions in the absence of Rh 2 (TPA) 4 and observed no background reaction. To ...

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