7H-PYRIDO(3,2,1-IJ) (2,1)BENZOXAZIEN DERIVATIVE

NEW MATERIAL:The derivative of formula I (R is H or lower alkyl) and its salt. EXAMPLE:9,10-Difluoro-7-oxo-1,2-dihydro-7H-pyrido[3,2,1-ij][2,1]benzox azine-6- carboxylic acid. USE:An intermediate for a compound of formula II (X is N-substituted 5- to 7-membered saturated cyclic amine) useful as a therapeutic agent for infection with Gram-negative and Gram-positive bacteria. PREPARATION:The objective compound of formula I can be produced by treating a compound of formula III with ethoxymethylenemalonic acid diethyl ester to obtain a compound of formula IV, converting the compound into an OH-protected compound of formula V by treating with acetic anhydride, heating the product together with a polyphosphoric acid ethyl ester, treating the resultant compound of formula VI with a halogenation agent, deprotecting by alkali treatment to obtain a compound of formula VII and treating the compound with an acid to effect intramolecular cyclization reaction.