The solvents were purified according to the standard procedures. Methyl 3-oxocyclobutane-3-carboxylate 6 and isatoic anhydride 21 were obtained from Enamine stock; all other starting materials were available commercially. Melting points were measured on the MPA100 OptiMelt automated melting point system. H and C NMR spectra were recorded on a Bruker 170 Avance 500 spectrometer (at 500 MHz for 1 H NMR, 126 MHz for C NMR), on Agilent ProPulse 600 spectrometer (at 500 MHz for 1 H and 151 MHz for 13 C) and Varian Unity Plus 400 spectrometer (at 400 MHz for 1 H NMR, 101 MHz for C NMR and 376 MHz for F NMR). NMR chemical shifts are reported in ppm (δ scale) downfield from TMS as an internal standard and are referenced using residual NMR solvent peaks at 7.26 and 77.16 ppm for 1 H and 13 C in CDCl3, 2.50 and 39.52 ppm for 1 H and C in DMSO-d6. For 19 F NMR CCl3F was used as internal standards. Coupling constants (J) are given in Hz. High-resolution mass spectra (HRMS) were obtained on an Agilent 1260 Infinity UHPLC instrument coupled with an Agilent 6224 Accurate Mass TOF mass spectrometer.