The scope of this transformation was assessed next using a series of different vinylbenzylcarbamate (1b-1g). 1b, 1c, 1d, 1e, 1f and 1g were synthesized and carried to the next step. The corresponding products 2b, 2c, 2d, 2e, 2f and 2g were isolated in moderate to acceptable yield from 40 to 66%. We discovered that this cascade reaction tolerated various electron-donating and electron-withdrawing groups, and that the outcome of this process is minimally perturbed by substitution on the aryl ring in position 4 and 5. However, the reaction does not tolerate substitution in the position 1 on the aryl ring as highlighted by the isolation of product 3h in 77% yield. In this case, 5-(trifluoromethyl)isoquinoline (3h) was observed along with unidentified by products. To evaluate whether this is due to steric or electron-withdrawing effects of the trifluoromethyl group, 1i was synthesized and carried to the next step. In this case also, was obtained in 19% yield confirming that steric hindrance has a major impact on the reaction outcome and yield. Finally, intrigued by the high sensitivity of reaction to steric effects, we synthesized reactant 1j which has a methyl group in α-position to the NHBoc group. Interestingly, steric hindrance in this position is well tolerated since two separable diasteroisomers 2j-1 and 2j-2 were isolated in 44% overall yield (22% each). This finding highlights the robustness of this cascade reaction for the construction of C-3-substituted tetrahydroisoquinolines. The keystone of the present cascade process are the successive formation of two iminium intermediates as shown in Scheme 2. Scheme 3. Substrate scope of the tetrahydro-3,4'-biisoquinoline synthesis.