IMINOPHOSPHORANE-MEDIATED SYNTHESIS OF 2H-INDAZOLE DERIVATIVES - PREPARATION OF 2,3-DIAMINO-2H-INDAZOLES BY INTRAMOLECULAR TRAPPING OF PHOSPHAZIDES AND 1H-1,2,4-TRIAZOLO[2,3-B]INDAZOLES BY A TANDEM AZA-WITTIG HETEROCUMULENE-MEDIATED STRATEGY

Treatment of o-azidobenzaldimines 2 with tertiary phosphines in methylene chloride at 0 °C leads to the corresponding 2,3-diamino-2H-indazole derivatives 3 by cyclization of the intermediate phosphazide. Compounds 3 react with isocyanates, carbon dioxide, and carbon disulfide to give the lH-l,2,4-triazolo[2,3-6]indazoles 8, 9, and 10, respectively. Compounds 8 can also be prepared from 2 in a one-pot reaction by sequential treatment with polystyryldiphenylphosphine and isocyanates. In tetrahydrofuran at room temperature, iminophosphoranes 3 react with acyl chlorides to form N-acyliminophosphoranes 11, which, under acid catalysis, undergo cyclization to yield the fused indazoles 12. © 1990, American Chemical Society. All rights reserved.