P-Trifluoromethyl ligands derived from Josiphos in the Ir-catalysed hydrogenation of 3,4-dihydroisoquinoline hydrochlorides
作者:R. Schwenk、A. Togni
DOI:10.1039/c5dt02019k
日期:——
Ferrocenyl phosphines containing a stereogenic P-CF3 group show improved selectivities in the Ir-catalysed hydrogenation of dihydroisoquinolinium derivatives.
(S)-(+)-1-Phenyl-1,2,3,4-tetrahydroisoquinoline, which is the key intermediate in preparing the urinary antispasmodic drug solifenacin, was racemized in quantitative yield by a simple one-pot procedure through N-chlorination with trichloroisocyanuric acid, conversion of the N-chloroamine into the imine hydrochloride, and reduction of the imine double bond. The racemized amine was successfully resolved by D-(-)-tartaric acid obtaining (S)-1-phenyl-1,2,3,4-tetrahydroisoquinoline in 81% yield and with 96.7% ee and, from the crystallization mother liquors, the R enriched form. This was racemized by the same one-pot process and resolved by D-(-)-tartaric acid with the same efficiency. Such an approach to the racemization of 1-phenyl-1,2,3,4-tetrahydroisoquinoline can be industrially useful to recycle the waste R enantiomer resulting from the classical resolution used to obtain the S enantiomer on a large scale.
NAGUBANDI SREERAMULU; FODOR G., J. HETEROCYCL. CHEM., 1980, 17, NO 7, 1457-1463