Denmark SE, Stavenger RA, Faucher AM, Edwards JP. Cyclopropanation with Diazomethane and Bis(oxazoline)palladium(II) Complexes.
J Org Chem 1997;
62:3375-3389. [PMID:
11671727 DOI:
10.1021/jo970044z]
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Abstract
Studies toward the development of an enantioselective diazomethane-based cyclopropanation reagent derived from bis(oxazoline)palladium(II) complexes are reported. Several simple palladium chelates, 2 and 7, in addition to the novel carbon-bound complexes 15 were synthesized and evaluated in the cyclopropanation of various electron-deficient olefins. The X-ray crystal structure of aryl-bis(oxazoline)palladium complex 15c is described. Although all catalysts efficiently affected cyclopropanation, all products were racemic. An intriguing relationship between substitution on the oxazoline ring, particularly the commonly-derivatized 4-position, and catalyst efficiency was discovered. The results are rationalized by either partial or complete bis(oxazoline) decomplexation during the course of the reaction.
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