Fischer indole synthesis of 3-benzyl-1H-indole via conductive and dielectric heating

As a part of designing one-pot synthesis conditions for a combination of Heck isomerization and Fischer indolization (HIFI sequence), a model reaction was studied using 3-phenylpropanal and phenylhydrazine to furnish 3-benzyl-1H-indole under conductive and dielectric heating. While Amberlyst® 15 as an acidic catalyst or T3P® (propylphosphonic acid cyclic anhydride) as a condensation agent gave high yields of 3-benzyl-1H-indole under both conductive and dielectric heating, these agents were not compatible with the conditions of the initial Heck isomerization. However, the catalyst-free thermal process for the indolization step proceeded with good yields in conjunction with the preceding Heck isomerization in a one-pot process under dielectric heating in N-methylpyrrolidone as a solvent.