Addition of RMgCl (R = n-Bu, Ph) to pinacol esters of 6-tosyloxy-1-alkenyl boronic acids at -78 degrees C gave the borates, which upon warming to room temperature underwent migration of R on boron to C(l) carbon and concomitant ring construction C-C bond formation between C(2) and C(6), eventually producing cyclopentyl alkyl (or aryl) carbinols after oxidative workup of the borane intermediates with 35% H2O2. Eight examples are presented and the reaction was applied to construction of a cyclohexyl carbinol.
Bedos, Bulletin de la Societe Chimique de France, 1926, vol. <4> 39, p. 480,485
作者:Bedos
DOI:——
日期:——
Investigation of Cyclization Reactions of Dicyclohexyl-6-iodo- and -6-tosylhexenylborane. A Facile Radical Cyclization Diverted to a Rearrangement−Cyclization with Base
作者:Diane M. Hinkens、M. Mark Midland
DOI:10.1021/jo900243q
日期:2009.6.5
Dicyclohexyl-6-iodohexenylborane efficiently undergoes radical cyclization at room temperature using tri-n-butyltin hydride as a hydrogen donor and without the aide of a radical initiator. Efforts to develop environmentally friendly reagents using hypophosphites as substitutes for tin hydrides in this reaction provided a 60% yield of cyclopentanemethanol when tetrabutylammonium hypophosphite was used. Air was necessary as an initiator when hypophosphites were used. During investigations of the radical cyclization reactions, it was discovered that excess tetrabutyl ammonium hydroxide provided the rearrangement-cyclization product in excellent yield. Since this product was chiral, efforts were focused on achieving enantioselectivity. Oxazaborolidines made from chiral amino alcohols and 6-tosy-1-hexenylboronic acid were treated with methyllithium to give 1-cyclopentylethanol after oxidation in 60% ee, demonstrating that oxazaborolidines were effective chiral directors for this reaction.