Synthesis of Triazolo Isoquinolines and Isochromenes from 2-Alkynylbenzaldehyde via Domino Reactions under Transition-Metal-Free Conditions
摘要:
We describe two simple straightforward syntheses of triazolo isoquinolines (3) and isochromenes (7) from 2-alkynylbenzaldehydes (1) as a common synthon. The synthetic strategy for 3 involves formation of the (E)-1-(2-nitrovinyl)-2-(alkynyl)benzene species 2 via condensation of synthon 1 with nitromethane followed by a [3 + 2] cycloaddition/extrusion of the nitro group/regioselective 6-endo cyclization domino sequence. In yet another strategy, the synthon 1 was condensed with nitromethane followed by electrophilic iodo cyclization of the resulting 2-nitro-1-(2-(alkynyl)phenyl)ethanol (6) to furnish iodo isochromene derivatives. The salient feature of the above two strategies involves formation of the corresponding heterocycles under metal-free conditions in good yields.
A highly efficient synthesis of [1,2,3]triazolo[5,1-a]isoquinoline derivatives was developed that proceeds through copper-catalyzed tandem Sonogashira coupling/regioselective 6-endo cyclization. This NH-triazole-directed annulation approach showed good functional-group tolerance and gave the corresponding N-fused heterocycles in good to excellent yields.