Panda, Kausik ; Suresh, J. R. ; Ila, H. ; Junjappa, H. (2003) Heteroaromatic annulation of 2-methyl/2-cyanomethylbenzimidazole dianions with α-oxoketene dithioacetals: a highly regioselective synthetic protocol for 1,2- and 2,3-substituted/annulated pyrido[1,2-a]benzimidazoles Journal of Organic Chemistry, 68 (9). pp. 3498-3506. ISSN 0022-3263
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Official URL: http://pubs.acs.org/doi/abs/10.1021/jo026786w
Related URL: http://dx.doi.org/10.1021/jo026786w
Abstract
A highly efficient and regioselective annulation protocol for a series of linearly 2,3- and angularly 1,2-substituted and annulated pyrido[1,2-a]benzimidazoles involving [3 + 3] cyclocondensation of the dianions generated from 2-methyl (2A) and 2-cyanomethyl (3A) benzimidazoles with a variety of α-oxoketene dithioacetals has been reported. Thus the dianion 2A derived from 2-methylbenzimidazole has been shown to undergo regioselective 1,2-addition with various α-oxoketene dithioacetals derived from acyclic (4a-d) and cyclic ketones (13a,b, 20, 29 and 32) to afford various carbinol acetals which on intramolecular cyclocondensation in the presence of phosphoric acid furnish the corresponding 1-methylthio-2,3-substituted (5a-c) and 2,3-fused linear polycyclic (14a,b, 21, 30, and 33) pyrido[1,2-a]benzimidazoles in high yields. Similarly the dianion 3A from 2-cyanomethylbenzimidazole undergoes one-pot conjugate addition-elimination and cyclocondensation with these α-oxoketene dithioacetals to give 4-cyano-3-(methylthio)-1(or 1,2-)-substituted (6a-d) and the corresponding angularly 1,2-fused (16a,b, 23, 31, and 34) polycylic analogues of pyrido[1,2-a]benzimidazoles in execellent yields.
Item Type: | Article |
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Source: | Copyright of this article belongs to American Chemical Society. |
ID Code: | 15286 |
Deposited On: | 13 Nov 2010 13:00 |
Last Modified: | 03 Jun 2011 04:47 |
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