Furopyridines. III. A new synthesis of furo[3,2‐ b ]pyridine

A convenient synthesis of furo[3,2‐ b ]pyridine and its 2‐ and 3‐methyl derivatives from ethyl 3‐hydroxypiconate ( 1 ) is described. The hydroxy ester 1 was O ‐alkylated with ethyl bromoacetate or ethyl 2‐bromopropionate to give the diester 2a or 2b . Cyclization of compound 2a afforded ethyl 3‐hydroxyfuro[3,2‐ b ]pyridine‐2‐carboxylate ( 3 ) which in turn was hydrolyzed and decarboxylated to give furo[3,2‐ b ]pyridin‐3‐(2 H )‐one ( 4a ). Cyclization of 2b gave the 2‐methyl derivative 4b . Reduction of 4a and 4b with sodium borohydride yielded the corresponding hydroxy derivative 5a and 5b respectively, which were dehydrated with phosphoric acid to give furo[3,2‐ b ]pyridine ( 6a ) and its 2‐methyl derivative ( 6b ). 2‐Acetylpyridin‐3‐ol ( 8 ) was converted to the ethoxycarbonylmethyl ether ( 9 ) by O ‐alkylation with ethyl bromoacetate, which was cyclized to give 3‐methylfuro[3,2‐ b ]pyridine‐2‐carboxylic acid ( 10 ). Decarboxylation of 10 afforded 3‐methylfuro[3,2‐ b ]pyridine ( 11 ).