The present invention provides compounds of the formula
wherein R is optionally substituted lower alkyl, cycloalkyl or aryl; R′ is alkyl or aryl; n is zero or an integer of 1 or 2; or an enantiomer thereof; or an enantiomeric mixture thereof.
The compounds of formula (I) are bridged C
2
-symmetric biphenyldiphosphine analogs and, thus, may be employed as ligands to generate chiral transition metal catalysts which may be applied in a variety of asymmetric reactions. The compounds of the present invention are easily accessible in high diastereomeric and optical purity according to the methods disclosed herein.
A New Class of Versatile Chiral-Bridged Atropisomeric Diphosphine Ligands: Remarkably Efficient Ligand Syntheses and Their Applications in Highly Enantioselective Hydrogenation Reactions
作者:Liqin Qiu、Fuk Yee Kwong、Jing Wu、Wai Har Lam、Shusun Chan、Wing-Yiu Yu、Yue-Ming Li、Rongwei Guo、Zhongyuan Zhou、Albert S. C. Chan
DOI:10.1021/ja0602694
日期:2006.5.1
A series of chiral diphosphineligands denoted as PQ-Phos was prepared by atropdiastereoselective Ullmann coupling and ring-closure reactions. The Ullmann coupling reaction of the biaryl diphosphine dioxides is featured by highlyefficient central-to-axial chirality transfer with diastereomeric excess >99%. This substrate-directed diastereomeric biaryl coupling reaction is unprecedented for the preparation