Racemic but tropos (chirally flexible) BIPHEP ligands for Rh(I)-complexes: highly enantioselective ene-type cyclization of 1,6-enynes.
[reaction: see text] The tropos (chirally flexible) or atropos (chirally rigid) nature of BIPHEP-Rh complexes at room temperature critically depends on the amines complexed. The aliphatic DPEN complex is atropos, whereas the aromatic DABN complex is tropos. BIPHEP-Rh chirality can thus be controlled by DABN at room temperature. The amine-free BIPHEP-Rh complex is tropos. At 5 degrees C, even amine-free BIPHEP-Rh complexes are atropos and hence can be used as enantiopure catalysts to give high enantioselectivity in ene-type cyclization of 1,6-enynes.
Department of Applied Chemistry, Tokyo Institute of Technology, Tokyo 152-8552, Japan. kmikami@o.cc.titech.ac.jp
Koichi
K
Mikami
Shohei
S
Kataoka
Yukinori
Y
Yusa
Kohsuke
K
Aikawa