Formation of an unexpected 3,3-diphenyl-3H-indazole through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate (Beilstein Journal of Organic Chemistry)

Abstract The one-pot reaction of 2,6-bis(diphenylmethyl)-4-methoxyaniline with tert-butylnitrite, BTEAC and DABSO in the presence of CuCl2 provided an unexpected 3H-indazole product 8. The structure of the compound was determined by HRMS, IR, NMR and further confirmed by single crystal X-ray crystallography. The compound crystallises in the triclinic P-1 space group, with unit cell parameters a = 9.2107 (4), b = 10.0413 (5), c = 14.4363 (6) Å, α = 78.183 (2), β = 87.625 (2), γ = 71.975 (2)°. The formation of 8 proceeded through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate 9. The molecules of 8 are organised by edge–face Ar–H···π, face–face π···π, and bifurcated OCH2–H···N interactions. In addition to these, there are Ar–H···H–Ar close contacts, (edge–edge and surrounding inversion centres) arranged as infinite tapes along the a direction. Beilstein J. Org. Chem. 2019, 15, 1347–1354. doi:10.3762/bjoc.15.134