Abstract
AbstractSeveral strategies for the immobilization of a L‐valine‐derived auxiliary on a Merrifield resin and on poly(ethylene glycol) are reported. The latter is shown to work excellently in asymmetric copper(II)‐catalyzed Michael reactions of cyclic β‐oxo esters 2 with methyl vinyl ketone (4), yielding the corresponding addition products 5 with quaternary stereocenter in selectivities of 97–99 % ee. The PEG‐supported auxiliary 1d can be precipitated from diethyl ether solutions and reused. A sulfur‐containing β‐oxo ester 2c was prepared in 92 % yield by a DMAP‐catalyzed transesterification method in order to detect enamine formation on solid support. The sulfur content can be used as an additional parameter in combustion analysis and therefore, may act as a diagnostic probe for enamine formation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
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