Access to pyrrolo-and pyrido [1,2-a] indole derivatives by intramoleclar nitrone cycloadditions. Effect of steric factors on the regioselective product formation

On starting from N-allyl substituted 2-indolecarbaldehydes and exploiting the intramolecular nitrone cycloaddition methodology, a number of the title fused-ring indole derivatives in racemic as well as enantiopure form were synthesized. The results show some degree of variability, particularly as the final hydrogenation step is concerned, there is no doubt that they are satisfactory in view of the planned target.