Aryne [3 + 2] cycloaddition with N-sulfonylpy ridinium imides and in situ generated N-sulfonylisoquinolinium imides: a potential route to pyrido[l,2-b] indazoles and indazolo[3,2-a]isoquinolines

摘要

The aryne [3 + 2] cycloaddition process with pyridinium imides breaks the aromaticity of the pyridine ring. By equipping the imide nitrogen with a sulfonyl group, the intermediate readily eliminates a sulfinate anion to restore the aromaticity, leading to the formation of pyrido[l,2-6]indazoles. The scope and limitation of this reaction are discussed. As an extension of this chemistry, N-tosylisoquinolinium imides, generated in situ from W-(2-alkynylbenzylidene)-tosylhydrazides via an AgOTf-catalyzed 6-endo-dig electrophilic cyclization, readily undergo aryne [3 + 2] cycloaddition to afford indazolo [3,2-a]-isoquinolines in the same pot, offering a highly efficient route to these potential anticancer agents.