Synthetic studies on the marine natural product halichondrins
H. Choi, D. 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.
*Lecture presented at the 14th International Conference
on Organic Synthesis (ICOS-14), Christchurch, New Zealand, 14-18 July
2002. Other presentations are published in this issue,
pp. 1-70.
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