A full account on rhodium‐catalyzed asymmetric, directed hydroboration of functionalized prochiral cyclopropenes affording enantiomerically enriched cyclopropylboronates is reported. The scope and limitations of two alternate directing groups, ester and carboxamide, are evaluated. It was found that hydroboration of esters appeared to be more sensitive to substitution in the aromatic ring of the substrates
Enantioselective, Facially Selective Carbomagnesation of Cyclopropenes
作者:Xiaozhong Liu、Joseph M. Fox
DOI:10.1021/ja058101q
日期:2006.5.1
Described is the facially selective and enantioselective addition of carbon nucleophiles to prochiral 3-hydroxymethylcyclopropenes. The process creates up to four stereocenters in a tandem addition/capture sequence that combines three simple materials to give complex and diverse products. The asymmetry is induced by the inexpensive and recoverable ligand (S)-N-methylprolinol. The enantioselectivity (90-98% ee with MeMgCl) is high for a range of cyclopropenes and electrophiles. Importantly, the diastereoselectivity is complementary to that obtained by enantioselective cyclopropanation with aryldiazoacetates. High enantioselectivities are obtained only when methoxide is included in the reaction. Evidence is provided that at least two chiral ligands are involved in the enantioselectivity-determining step.