Efficient Synthesis of Highly Functionalized Indazoles and 2,3-Dihydro-1,2-benzisoxazoles by Reaction of Stable Fischer Dienyl Carbenes and Isocyanides

A range of stable chromium and tungsten Fischer dienyl carbenes have been prepared by [3+2] cycloaddition of alkenylethynyl carbene complexes with nitrones or diazoalkanes. Treatment of these systems with isocyanides gives entry to highly functionalized 2,3‐dihydro‐1,2‐benzisoxazoles and indazoles in a completely regioselective fashion, under mild conditions, and with high yields. This methodology can be also applied to the preparation of analogous naphthoisoxazoles starting from arylethynyl Fischer complexes. Reductive cleavage of the isoxazole moiety in the prepared heterocycles also enables the efficient synthesis of highly substituted p‐aminophenols. Se han preparado varios ejemplos de complejos dienil carbeno de Fischer estables, de cromo y de volframio, por reacción de cicloadición [3+2] entre alqueniletinil complejos carbeno y nitronas o diazoalcanos. El tratamiento de estos sistemas con dos equivalentes de un isocianuro permite obtener 2,3‐dihidro‐1,2‐benzisoxazoles e indazoles altamente funcionalizados de forma completamente regioselectiva, en condiciones suaves y con altos rendimentos. La misma metodología puede aplicarse a la preparación de naftoisoxazoles a partir de ariletinil carbenos de Fischer. La ruptura en condiciones reductoras del enlace nitrógeno‐oxígeno del anillo de isoxazol previamente obtenido conduce a p‐aminofenoles sustituidos con excelentes rendimientos. Novel stable Fischer dienyl complexes, arising from the [3+2] cycloaddition of alkenylethynyl carbene complexes and nitrones or diazoalkanes, have been utilized for the regioselective and effective synthesis of benzisoxazole and indazole derivatives by means of their reaction with isocyanides (see scheme).