Identification of reaction intermediates in AlCl3-mediated cyclocondensation reactions by simultaneous in situ ATR-FTIR and UV–vis spectroscopy

Functionalized trifluoromethyl-substituted salicylates have been synthesized based on AlCl3-mediated cyclocondensation reactions using 4,4-dimethoxy-1,1,1-trifluorobut-3-en-2-one and 1,3-bis(silyloxy)-1,3-butadienes. Simultaneous in situ ATR-FTIR/UV–vis spectroscopic measurements were carried out for mechanistic studies. Real-time in situ spectroscopic investigations reveal the formation of an aluminum trichloride bidentate-butenone adduct as intermediate. The observed band shifts in the respective UV–vis spectra in consequence of complex formation could be explained by theoretical calculations. Lewis acidic solids (Al2O3 and TiO2) were also successfully utilized. Due to the strong substrate adsorption on the solids detected by UV–vis-DRS and FTIR transmission spectroscopy the obtained yields were rather modest.