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Catalytic Asymmetric Dichlorination of Allylic Alcohols
K. C. Nicolaou*, N. L. Simmons, Y. Ying, P. M. Heretsch, J. S. Chen
The Scripps Research Institute, La Jolla and University of California San Diego, La Jolla, USA
20 July 2011 (online)
Nicolaou and co-workers report a catalytic asymmetric dichlorination of allylic alcohols. The Sharpless ligand (DHQ)2PHAL (1) displayed certain potential for this transformation and promoted the dichlorination of different allylic alcohols with moderate to good yields and promising to good enantioselectivities. 4-Ph(C6H4)ICl2 was found to be the chlorine source of choice in terms of enantioselectivity. The reaction was found to be stereospecific, giving trans products from E-olefins and cis products from Z-olefins, presumably via intermediary chlorenium ion formation. The stereochemical rational for this step involves the generation of an electrophilic chlorine source by the reaction of the aryl iododichloride with one quinuclidine moiety and preorganization of the allylic alcohol through hydrogen bonding with the phthalazine.