1,2-Ferrocenediylazaphosphinines 3: A New Class of Planar Chiral Ligands for Cu-Catalyzed Cyclopropanation
Seung Hwan Paek, Thanh-Thien Co, Dong Ho Lee, Yu Chul Park, and Tae-Jeong Kim
Bull. Korean Chem. Soc. 2002, Vol. 23, No. 12, 1702
Abstract:
The synthesis and catalytic application of a new class of planar chiral ferrocenes, 1,2-ferrocenediylazaphosphinines (1 and 2) are described. They are powerful ligands for the copper(I)-catalyzed asymmetric cyclopropanation of a range of alkenes with diazo esters to exhibit an exceptionally high degree of diastereoselectivity (~100% de) in favor of trans isomers, regardless the structure of the olefins and the diazo compounds. Comparative studies between 1 and 2 reveal that the former works better in terms of diastereocontrol. In contrast, however, enantioselectivity is low with both 1 and 2 as a whole although, in certain cases with a proper combination of the olefin and the diazo ester, high optical yields (up to 100% ee) can be achieved. Other reaction parameters such as the reaction temperature and the structure of the ligand do exhibit some influence, although infinitestimal, on both chemical and optical yields.