1,3-Dipolar cycloaddition reactions of 1-(3-nitrophenacyl)-1,10-phenanthrolinium N-ylide with activated alkynes

The 3+2 cycloaddition reaction of 1-(3-nitrophenacyl)-1,10-phenanthrolinium ylide 4 with activated alkynes gave pyrrolo(1,2-a)(1,10)phenanthrolines 7a-e. The reaction of N-ylide 4 with DMAD, under controlled conditions, gave regioselectively the primary cycloadduct trans-5a which, in the presence of triethylamine, rearranged regio- and stereoselectively to trans-6a. Evidence for the helical chirality of pyrrolophenanthrolines 7b-e was obtained by NMR spectroscopy.