Facile Regioselective Synthesis of Pyrazolo[5,1-a]isoquinolines via Ring-Opening Cyclization/Oxidation Reactions of Stable Aroyldiaziridines of 3,4-Tetrahydroisoquinoline with Alkynes

Abstract

Newly prepared, stable aroyldiaziridines of 3,4-tetrahydroisoquinolines undergo regioselective cycloaddition reactions with a number of both mono and disubstituted alkynes, affording five-membered ring products which, after oxidative aromatization of the pyrazoline ring, lead to the efficient preparation of pyrazolo[5,1-a]isoquinolines. The overall transformation is base-catalyzed and occurs more rapidly in the presence of oxygen, in halogenated solvents and in dioxane.

Key words

isoquinolines - diaziridines - cycloadditions - alkynes - oxidations

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CCDC 643312 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.