Highly selective partial dehydrogenation of tetrahydroisoquinolines using modified Pd/C

A highly selective procedure has been developed for the partial dehydrogenation of 1-substituted-1,2,3,4-tetrahydroisoquinolines over K3PO4·3H2O-modified Pd/C catalyst. This new method provides facile, atom-economical and environmentally friendly access to 1-substituted-3,4-dihydroisoquinolines without the need for stoichiometric amounts of harmful oxidants. The use of standard Pd/C as a catalyst for this process gave poor chemoselectivity. Pleasingly, the use of a K3PO4·3H2O-modified Pd/C catalyst promoted the partial dehydrogenation of 1-substituted-1,2,3,4-tetrahydroisoquinolines with excellent chemoselectivity by suppressing further dehydroaromatization. Furthermore, conducting the reaction under an atmosphere of oxygen led to further improvements in the chemoselectivity of the dehydrogenation, with the ratio of imine to isoquinoline reaching up to 32/1. The heterogenous Pd/C catalyst could also be recycled and reused at least three times with excellent conversion and chemoselectivity, demonstrating the significantly practical potential of this methodology.

Graphical AbstractA highly selective reaction has been developed for the partial dehydrogenation of 1-substituted-1,2,3,4-tetrahydroisoquinolines using a K3PO4.3H2O-modified Pd/C catalyst, which can be readily recycled and reused. This reaction provides facile and atom-economical access to 1-substituted-3,4-dihydroisoquinolines with excellent chemoselectivity by suppressing further dehydroaromatization.Figure optionsDownload full-size imageDownload as PowerPoint slide