Pyridines—continued nitro

Among other condensed thiazole ring systems, imidazo[2,l-6]thiazoles (tetramisole is a member of this class), thiazolo-pyrimidines, and thiazolo-pyridines continue to attract the most interest. Attention is concentrated on synthesis and biological activity. Unexpectedly, dihydrothiazolo[3,2-a]pyridinium bromide is readily brominated when the pyridine ring has a 3-nitro-substituent but not when it has a 3-amino-substituent. 

A well-stirred solution of 6.8 g of the mixed isomers of 1 -(2,3,6-tri-methoxyphenyl)propene in 40 g of dry acetone was treated with 3.2 g pyridine and cooled to 0 °C with an external ice bath. There was then added 6.5 g tetranitro-methane over the course of 1 min, the stirring was continued for an additional 2 min, and then the reaction mixture was quenched by the addition of 2.2 g KOH in 40 mL H20. There was additional H,0 added, and the organics were extracted with 3x75 mL CH,C12. The solvent from the pooled extracts was removed under vacuum, and the 5.3 g residue distilled at 0.2 mm/Hg. A fraction boiling at 150-170 °C proved to be largely 2,3,6-trimethoxybenzaldehyde. A second fraction (170-200 °C at 0.2 mm/Hg) also spontaneously crystallized to a yellow solid. This was recrystallized from MeOH to provide, after drying to constant weight, 2.8 g of 2-nitro-1 -(2,3,6-trimethoxyphenyl)propene with a mp of 73-74 °C. Anal. (C 2H N05) C,H. 

Thiophen Analogues of Quinoline.— Interest in the chemistry of thieno-pyridines is continuing. Thieno[3,2-b]pyridine has been prepared in 80% yield through the zinc-chloride-catalysed condensation of 3-aminothiophen hydrochloride with malonic aldehyde acetal. Reaction of the 2-amino-3-benzylthiophen (425) with l-nitro-2,2-bis(methylmercapto)ethylene (426) gave the thieno[2,3-b]pyndine derivative (427) in 29% yield. 5-Ethylthieno-... 

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