Regioselective synthesis of 2H-indazoles using a mild, one-pot condensation-Cadogan reductive cyclization.
An operationally simple and efficient one-pot synthesis of 2H-indazoles from commercially available reagents is reported. Ortho-imino-nitrobenzene substrates, generated via condensation, undergo reductive cyclization promoted by tri-n-butylphosophine to afford substituted 2H-indazoles under mild reaction conditions. A variety of electronically diverse ortho-nitrobenzaldehydes and anilines were examined. To further extend the scope of the transformation, aliphatic amines were also employed to form N2-alkyl indazoles selectively under the optimized reaction conditions.
CVMED Medicinal Chemistry, Pfizer Inc. , Eastern Point Road, Groton, Connecticut 06340, United States.
Nathan E
NE
Genung
Liuqing
L
Wei
Gary E
GE
Aspnes
D001547:Benzaldehydes / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D007191:Indazoles / Q000138:chemical synthesis* / Q000737:chemistry*; D007202:Indicators and Reagents / Q000737:chemistry; D015394:Molecular Structure; D009578:Nitrobenzenes / Q000737:chemistry
D001547:Benzaldehydes; D007191:Indazoles; D007202:Indicators and Reagents; D009578:Nitrobenzenes; C043850:2-nitrobenzaldehyde; C036077:nitrobenzene