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Pure Appl. Chem., 2003, Vol. 75, No. 1, pp. 1-17

Synthetic studies on the marine natural product halichondrins

Hyeong-wook Choi, Damtew Demeke, F.-A. Kang, Y. Kishi, K. Nakajima, P. Nowak, Z.-K. Wan and C. Xie

Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA

Abstract: In connection with the de elopment of a practical synthesis of the right half, and its analog E7389, of halichondrin B, an efficient and scalable synthesis of the two major building blocks is reported. In addition, a new synthesis of the C20–C26 segment via a regiospecific and stereoselecti e SN2' process is presented. A sulfonamide class of ligands is shown to be effective for asymmetric Ni/Cr-mediated reactions under both stoichiometric and catalytic conditions, and the X-ray structure reveals this class of ligands to be tridentate. On the basis of three X-ray structures, a possible mechanism is suggested for this process. Stable and crystalline Cr(III)/sulfonamide complexes are shown to be effective for catalytic Cr-mediated coupling reactions of allyl, alkenyl, and alkyl halides with aldehydes, and some examples for application of the stoichiometric and catalytic asymmetric processes are presented.