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U. Jordis, F. Sauter, M. Burkart, H. Henning, A. Gelbing:
"Synthesis of novel quinolone chemotherapeutics. V. Methodical investigations on the synthesis of quinolone chemotherapeutics";
Journal für Praktische Chemie, 333 (2) (1991), 267 - 279.

Condensation of N-ethylanilines with 5-(methoxymethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (Meldrum's acid deriv.) gave 5-[[N-ethyl-N-(4-fluorohalophenyl)amino]methylene]-2,2-dimethyl-1,3-dioxane-4,6-diones which upon cyclocondensation gave N-ethyl-1,4-dihydro-4-oxoquinoline-3-carboxylic acids I (X = F, Cl). Complexation of I with BF3.OEt2 or BBr3 gave the resp. anhydrides of dibromo- or difluoroboric acid; the latter facilitated the nucleophilic arom. substitution reaction of these compds. (e.g., with N-methylpiperazine). The anhydride of I (X = F) with difluoroboric acid was treated with N-methylpiperazine to give the N-ethyl-6-fluoro-1,4-dihydro-7-(N-methylpiperazino)-4-oxoquinoline-3-carboxylic acid deriv. which was hydrolyzed to give pefloxacin. The kinetics of arom. nucleophilic substitution of difluoroboric anhydrides of I with N-methylpiperazine were studied.
AN 1991:583048