Issue in Honor of Prof. Alexandru T. Balaban ARKIVOC 2005 (x) 165-173
1,3-Dipolar cycloaddition reactions of 1-(3-nitrophenacyl)-1,10phenanthrolinium N-ylide with activated alkynes
Florea Dumitrascu,1* Constantin Draghici,1 Mino R. Caira,2 Andrei Badoiu,1 Loredana Barbu,1and Mihaela Cristea1
1 Centre of Organic Chemistry "C. D. Nenitzescu", Romanian Academy, Spl. Independentei 202B, Bucharest 060023, Romania, 2 Department of Chemistry, University of Cape Town, Rondebosch 7701, South Africa E-mail:
[email protected]
Dedicated to Professor Alexandru Balaban on his 75th birthday (received 06 Dec 04; accepted 22 Apr 05; published on the web 12 May 05)
Abstract 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.
Keywords: 1,10-Phenanthrolinium N-ylide, 1,3-dipolar cycloaddition, regio-and stereoselectivity, pyrrolophenanthrolines, helical chirality
Introduction
The use of heteroaromatic N-ylides as 1,3-dipoles has gained increasing interest due to the possibility of obtaining new condensed heterocyclic structures difficult to obtain by other methods.1-5 The dipolar 3+2 cycloaddition of dipolarophiles to heteroaromatic N-ylides raises interesting regio- and stereoselectivity problems.5-9 Recently, the synthesis of a new heterocyclic system, namely pyrrolo[1,2-a][1,10]phenanthroline, by 1,3-dipolar cycloaddition of 1,10phenanthrolinium N-ylides with acetylenic dipolarophiles, was described.9-12 The extended heteroaromatic system presents helical chirality, like that of the helicene-type compounds.13
Herein we describe the reaction of 1-(3-nitrophenacyl)-1,10-phenanthrolinium N-ylide (4) with activated alkynes giving new pyrrolo[1,2-a][1,10]phenanthrolines 7a-d.
ISSN 1424-6376 Page 165 ©ARKAT USA, Inc
