Chemical process and intermediates used therein

A process for the manufacture of an imidazo [4,5-b]pyridine of the formula I ##STR6## or a physiologically acceptable salt thereof, wherein R.sup.1 is (1-6C)alkyl;

• R.sup.2 is hydrogen or halogeno;
• and R.sup.3 and R.sup.4 are selected from hydrogen, halogeno, (1-6C)alkyl, (1-6C)alkoxy, hydroxymethyl and hydroxy;
• which is characterised in that a compound of the formula II ##STR7## wherein P.sup.1 is an electron-deficient phenyl group or is a pyridyl or pyrimidyl group, is reacted with a base selected from an alkali metal hydroxide, (1-12C)alkanolate, (1-12C)alkanethiolate, phenolate, thiophenolate and diphenylphosphide, wherein any phenyl ring of the latter three groups may optionally bear a (1-4C)alkyl, (1-4C)alkoxy or halogeno substituent;
• whereafter:
• when a physiologically acceptable salt of a compound of formula I is required, it is obtained by reaction with the appropriate acid or base affording a physiologically acceptable ion, or by any other conventional salt formation procedure;
• and when an optically active form of a compound of formula I is required, the process is carried out with an optically active form of the starting material of formula II, or a racemic form of a compound of formula I is resolved using a conventional procedure;
• and wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 and P.sup.1 have any of the meanings defined above.