D. Levendis, Jeffrey S. Moffit, B. Staskun
Oct 1, 1999
Citations
0
Influential Citations
0
Citations
Journal
Journal of Chemical Research
Abstract
In a recent! communication we showed that a I-alkyl-I,4dihydro-4-oxoquinoline-3-carboxylic acid 1 is converted by SOCIz to a product surmised to be an acid chloride-hydrogen chloride complex which on treatment with aqueous amine gave a 4-imino acid while with dry amine the principle outcome was a 4-imino amide. In a natural extension of the work to the 2-methyl analogues, title acid 2 was refluxed with excess SOCIz (especially purified.' or reagent as received) for I h and here we report on the extraordinary outcome in which: (i) the purified product (70-80% crude yield) contained a sulfur atom from the reagent which had somehow become incorporated in reduced form into a new five-membered ring; (ii) the 2-methyl group in 2 was chlorinated; (iii) the 4-oxo function in 2 was replaced by chlorine, and (iv) the ethyl group on N had been eliminated-all in a one-pot reaction. Events as in (i) and (ii) had earlier been observed when 4-methylnicotinic acid! and a 2-methylquinoline-3carboxylic acid" were refluxed with SOCIz, while those as in (iii) and (iv) had also been documented.! but this is the first instance of all four reactions having collectively occurred in one procedure. Characterisation of the product as 3,3,9-trichlorothieno[3,4-b]quinolin-I(3H)-one 4 was made from its spectral eH NMR, MS) properties and elementary analysis, and was unequivocally established from an X-ray crystallographic determination (Fig. 1). The mirror site symmetry of the molecule in the space group C2/m implies that all the atoms except for CI(2) are co-planar. The analogous 6-fluorothieno[3,4-b]quinolinone 5 was similarly obtained from the 7-fluoro-4-oxo acid 3 and SOCIz. In contrast, the l-ethyl substituent in 4-oxo acid 1 is retained after similar treatment with SOCIz;1 it would appear that attachment of a dihydrothiophene-like functionality as in 4 and 5 enhances the tendency to eliminate the 4-alkyl group (vide infra). Another surprise was the relative ease with which the thieno[3,4-b]quinoline framework was formed from the reactants. Thus merely keeping a mixture of carboxylic acid 2 and SOCIz at room temperature for 24 h led to 3,3-dichloro-4-ethylthieno[3 ,4-b[quinoline-I (3H),9(4H)-dione 6 (80-90%, crude yield). This assignment was unequivocally confirmed in the case of the 6-fluoro analogue 7 (likewise derived from carboxylic acid 3) from an X-ray