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Cyclopentane Construction by Rh-Catalyzed Intramolecular C−H Insertion:  Relative Reactivity of a Range of Catalysts

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journal contribution
posted on 11.06.2004, 00:00 by Douglass F. Taber, Pramod V. Joshi
The preparation and Rh-mediated cyclization of the α-diazoester 1 are outlined, and its utility in determining the elements that contribute to the reactivity of the intermediate Rh-carbenoid is presented. The rate of disappearance of diazo ester 1 catalyzed by several representative Rh(II) complexes was determined. The observed relative rate constants for the reaction of the Rh(II) complexes with 1 varied over a range of >107. The reactivity of the Rh-carbenoid intermediate was explored using the ratio of the sum of (3 + 4 + 5) to 2 (cyclization vs elimination), the ratio of 3 to the sum of (4 + 5) (chemoselectivity), and the ratio of 4 to 5 (diastereoselectivity). It is striking that these four measures of reactivity were found to be independent of each other.