Regioselectively photoinduced synthesis, NMR analysis and X-ray crystal structure of novel benzocyclobutenes

•An efficient, green, and concise approach for the synthesis of novel BCBs is described.•BCBs were synthesized under environmentally friendly conditions with perfect regioselectivity.•1D-NMR and 2D-NMR of 3aa were conducted in details to verify the anti-conformation.•Single-crystal X-ray diffraction analysis further confirmed the anti-conformation of title BCBs. An efficient, green, and concise tandem vinylogous aldol and [2 + 2] photocycloaddition reaction for the regioselective synthesis of novel benzocyclobutenes (BCBs) starting from readily available 2-methylbenzophenone and isatin under extremely mild and eco-friendly conditions without using any photocatalysts is reported. The BCB products could be obtained under UV LEDs (365 nm) irradiation at room temperature in 18 h with perfect regioselectivity and definite compatibilities with functional groups. To discuss the characteristic pattern of cyclobutene proton, to identify its anti-conformation, NMR spectra analysis was carried out in details by the chemical shifts, couplings (1D-NMR) and correlations (2D-NMR). X-ray diffraction of 3aa confirmed its anti-conformation, and all the compounds were unequivocally confirmed by NMR, HRMS and XRD analysis. XRD analysis of 3aa further aids to disclose the reason why the benzene benzene and isatin rings are roughly in parallel.