The Darzens condensation of symmetric and unsymmetric ketones with (-)-8-phenylmenthyl a-chloroacetate diastereoselectively affords glycidic esters in 77-94% de; the stereochemistry [(2R,3R) configuration] of the product is understandable in terms of n-n interaction in the open transition state model.The epoxide functionality has been demonstrated to be a versatile and useful moiety for organic synthesis.' Our approach to the asymmetric synthesis of epoxides is based on the Darzens glycidic ester condensation, which is one of the more reliable methods for the construction of a,P-epoxy esters.2 Since the Darzens reaction formally consists of an initial aldol type addition, followed by an intramolecular S N ~ rea~tion,3-~ the high stereoselectivity in such a reactions is mostly induced in the initial ~tep.37~ Therefore, little attention has been shown to the stereoselective Darzens reaction of ketones, especially symmetric 0nes.~,5 In this communication we describe the highly asymmetric Darzens reaction of ketones with achloroacetate using the (-)-8-phenylmenthyl group? as a chiral auxiliary, as shown in Scheme 1. l a R = M e (2R)-2-6 (257-2-6 b R = (-)-menthy1
Asymmetric Induction in Darzens Condensation by Means of (-)-8-Phenylmenthyl and (-)-Menthyl Auxiliaries.-The Darzens condensation of symmetric ketones like (I) or the ketones (IV) with (-)-8-phenylmenthyl halogenoacetates is found to proceed with good to high diastereoselectivity.Moderate diastereoselectivity is observed with benzaldehyde and N-benzylideneaniline.Using (-)-menthyl as auxiliary low stereoselectivity is found. -(TAKAGI, R.; KIMURA, J.; SHINOHARA, Y.; OHBA, Y.; TAKEZONO, K.; HIRAGA, Y.; KOJIMA, S.; OHKATA, K.; J.
1997 stereochemistry stereochemistry (general, optical resolution) O 0030 10 -030 Asymmetric Darzens Condensation of Ketones with α-Chloroacetates by Means of (-)-8-Phenylmenthyl Auxiliary. -The Darzens condensation of symmetric and unsymmetric ketones (II) and (IV) with the chloroacetate (I) affords glycidic esters in 77-94% d.e.; the (2R,3R) stereochemistry of the main diastereomers (III) and (V) is explained in terms of π-π interaction in the open transition state model. -(OHKATA, K.; KIMURA, J.; SHINOHARA, Y.; TAKAGI, R.; HIRAGA, Y.; Chem.
Alkohole (II) und das Nitrophenol (I) reagieren miteinander in Gegenwart von Azodicarbonsäurediethyl‐ ester (III) und Triphenylphosphin (IV) zu den aci‐Nitroestern (V), die mit dem Phosphorylid (VI) zu den substituierten Acrylsäureestern (VII) und dem p‐Benzochinonmonoxim (VIII) umgesetzt werden.
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