Studies on the factors controlling the stereoselectivity in electrophilic iodocyclization of alkylidenecyclopropyl ketones
摘要:
An efficient electrophilic iodocyclization of alkylidenecyclopropyl ketones with N-iodosuccinimide (NIS) or l(2) in aqueous CH3CN affording 3-oxabicyclo[3.1.0]hexan-2-ols is described. NIS is a better electrophilic iodocyclization reagent than l(2). Four chiral centers were formed within one step. The stereochemistry was established by the X-ray diffraction studies of compounds 2e-2h, 2n, and 2c. It is quite interesting to observe that the substituent of the cyclopropane ring plays an important role in determining the relative stereochemistry at the 4-position: with R-2 being an acyl or ester group a mixture of (1S*,2R*,4S*5R*)-2 (major) and (1R*,2R*,4R*,5R*)-2 (minor) was formed with moderate selectivity while the reaction of the substrates with R being sulfonyl and p-methylphenylsulfonyl or R-1 being phenyl afforded (1R*,2R*,4S*,5S*)-2 or (1S*,2R*,4S*,5R*)-2f as the only product. The reaction is general for a range of different substrates to afford the products in moderate to high yields. (C) 2008 Elsevier Ltd. All rights reserved.