A palladium-catalyzed asymmetric O-H insertion reaction was developed. Palladium complexes with chiral spiro bisoxazoline ligands promoted the insertion of α-aryl-α-diazoacetates into the O-H bond of phenols with high yield and excellent enantioselectivity under mild reaction conditions. This palladium-catalyzed asymmetric O-H insertion reaction provided an efficient and highly enantioselective method for the preparation of synthetically useful optically active α-aryl-α-aryloxyacetates.
A new highly enantioselective route to α-alkenyl α-amino acid derivatives using a N–H insertion reaction of vinyldiazoacetates and tert-butyl carbamate cooperatively catalyzed by achiral dirhodium(ii) carboxylates and chiral spiro phosphoric acids was developed.
A palladium-catalyzed asymmetric O À H insertion reaction was developed. Palladium complexes with chiral spiro bisoxazoline ligands promoted the insertion of a-aryl-adiazoacetates into the OÀH bond of phenols with high yield and excellent enantioselectivity under mild reaction conditions. This palladium-catalyzed asymmetric O À H insertion reaction provided an efficient and highly enantioselective method for the preparation of synthetically useful optically active a-aryl-aaryloxyacetates.Palladium is an indispensable and versatile catalyst in modern organic synthesis.[1] Palladium efficiently catalyzes the cyclopropanation of olefins with diazomethane, a widely used carbene-transfer reaction, [2] and various new palladiumcatalyzed carbene-transfer reactions based on migratory insertion have recently been developed.[3] However, asymmetric palladium-catalyzed carbene-transfer reactions are rare and remain a challenge. The early examples of palladium-catalyzed asymmetric carbene-transfer reactions involved cyclopropanations and carbenylative amination, however, the resulting enantioselectivity was unsatisfactory. [4] Recently, Hu and co-workers [5] reported highly enantioselective palladium-catalyzed three-component reactions of pyrrole, diazoesters, and imines. Herein, we report a palladiumcatalyzed asymmetric insertion of a-aryl-a-diazoacetates into the O À H bond of phenols (Scheme 1).[6] Palladium complexes with chiral spiro bisoxazoline ligands efficiently catalyzed the OÀH insertion reaction, which provides a new method for the preparation of a-aryl-a-aryloxyacetates 3 with good yields and excellent enantioselectivity under mild, neutral reaction conditions.The a-aryl-a-aryloxyacetate moiety is ubiquitous in biologically active molecules [7] and it is also present in a chiral solvating agent for NMR spectroscopy [8] (Scheme 1). The established methodologies for the synthesis of optically active a-aryl-a-aryloxyacetates are based on either multistep transformations from chiral starting materials or the use of chiral auxiliaries. [7,8] To our knowledge, no highly enantioselective catalytic asymmetric method for preparing these important compounds has been reported. [9] The challenges lie mainly in the high acidity of the ahydrogen of a-aryl-a-aryloxyacetates. Because these compounds readily epimerize under basic conditions or at high temperature, any reliable method for their preparation should involve mild, neutral conditions. The transition-metal-catalyzed OÀH insertion reaction meets this requirement. In 2006, Maier and Fu [6c] attempted an OÀH bond insertion reaction between a-diazo-a-phenylacetates and phenols by using chiral copper bisazaferrocene complexes as catalysts. However, the desired O À H insertion product (a-phenoxy-aphenylacetate) was obtained in 56 % yield with only 11 % ee. We [6d] and Uozumi and co-workers [6g] used chiral copper spiro bisoxazoline complexes and a chiral copper imidazoindolephosphine complex, respectively, for the same reaction and also obtained extremely l...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.