Synthesis of benzo[ b ][1,5]diazocin-6(5 H )-one derivatives via the Cu-catalysed oxidative cyclization of 2-aryl-1 H -indoles with 1,1-enediamines.

A novel protocol for the synthesis of highly functionalized benzo[ b ][1,5]diazocin-6(5 H )-one derivatives (BDCOs, 4 and 5) from 2-aryl-1 H -indoles and 1,1-enediamines was developed via a complex cascade of reactions including regioselective free radical oxidation, the 1,2-addition of imine, imine-enamine tautomerization, intramolecular cyclization, and ring expansion. The cascade reaction was enabled by refluxing a mixture of two substrates in the presence of di- tert -butyl peroxide (DTBP) as an oxidant and anhydrous CuI as a catalyst in toluene under argon protection. Consequently, a series of BDCOs (4 and 5) were synthesized with high regioselectivity in good yield. This protocol can be used for the synthesis of functionalized BDCOs via a one-pot oxidative annulation reaction rather than a multi-step reaction, which is suitable for both combinatorial and parallel syntheses of BDCOs.