5-Aminofuro[3,2-c]pyridinium tosylates 2a-2c were synthesized by direct N-amination of furo[3,2-c]pyridines 1a-1c with O-(4-methylbenzenesulfonyl)hydroxylamine in dichloromethane. Zwitterionic furo[3,2-c]pyridinium N-imides 3a-3c generated from 2a-2c and anhydrous potassium carbonate in N,N-dimethylformamide afforded by 1,3-dipolar cycloaddition reactions with dimethyl butynedioate or ethyl propiolate the corresponding furo[3,2-c]pyrazolo[1,5-a]pyridinecarboxylic esters 4a-4c and 5a-5c. Furo[3,2-c]pyridine N-oxides 6a-6c and their benzo derivative 6d were synthesized by reaction of 1 with 3-chloroperbenzoic acid in dichloromethane. Treatment of N-oxides 6 with benzoyl chloride and cyanide anion (Reissert-Henze reaction) was shown to produce the corresponding furo[3,2-c]pyridine-4-carbonitriles 7. In further transformations (acid and alkaline hydrolysis), the cyano group was converted successively to amide and carboxylic acid.
通过二氯甲烷中的直接N-烷基化,合成了5-氨基呋[3,2-c]吡啶基甲磺酸盐2a-2c,其中呋[3,2-c]吡啶1a-1c与O-(对甲苯磺酰)羟胺发生N-烷基化反应。通过2a-2c和无水碳酸钾在N,N-二甲基甲酰胺中生成带电呋[3,2-c]吡啶基N-亚胺3a-3c,再通过与二甲基丁二酸酯或丙炔酸乙酯的1,3-偶极环加成反应,得到相应的呋[3,2-c]吡唑并[1,5-a]吡啶羧酸酯4a-4c和5a-5c。通过呋[3,2-c]吡啶基N-氧化物6a-6c及其苯并衍生物6d与二氯甲烷中的3-氯过氧苯甲酸反应合成。将N-氧化物6与苯甲酰氯和氰根离子(Reissert-Henze反应)处理后,可生成相应的呋[3,2-c]吡啶-4-碳腈7。在进一步的转化中(酸性和碱性水解),腈基依次转化为酰胺和羧酸。