Thieno naphthyridines, syntheses

Japanese workers recently designed a synthesis of 5-amino-2,3-dihydrothiepino[2,3- >]pyridine-4-carbonitrile 2 based on Thorpe-Ziegler cyclisation of 2-(3-cyanopropylthio)pyridine-3-carbonitrile 1. Treatment of 1 with potassium t-butoxide however, did not, give 2, but produced the thieno[2,3-/i][l,6]naphthyridine 3 in 82% yield. 

Treatment with sodium ethoxide of thioethers 316, prepared by the reaction of l,2,5,6,7,8-hexahydro-l,6-naphthyridine-2thiones 317 with halo ketones, esters, amides or nitriles, resulted in the synthesis of thieno[2,3-Z>]-l,6-naphthyridines 318 (1993BCJ3716). 

The synthesis and biological activity of 2-(alkoxycarbonyl)thieno[2,3-c]-2,7-nap-hthyridine and isothiazolo[4,5-Z>]-2,7-naphthyridine derivatives have been described (2002MI3, 2002MI4). 

Procedures for the synthesis of compounds containing a five-membered heterocycle with a linearly fused 1,8-naphthyridine fragment (thiazolo[5,4-Z>]- (1979CPB410), imidazolo[4,5-Z>]-, triazolo[4,5-Z>]- (1980CPB235), oxazolo[5,4-/ ]-, thiadiazolo[5,4-b]-, isothiazolo[5,4-Z>]-, pyrazolo[3,4-Z>]-, thieno[2,3-Z>]-, furo[2,3-/ ]-l,8-naphthyridines (1980CPB761, 1984CPB4914)) were described and the antibacterial activity of these compounds was studied. 

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