Photo-on-Demand In Situ Synthesis of N-Substituted Trichloroacetamides with Tetrachloroethylene and Their Conversions...

N-substituted trichloroacetamides (NTCAs), which serve as blocked isocyanates, were synthesized in ∼97% yields by in situ photo-on-demand trichloroacetylation of amines with tetrachloroethylene (TCE). The reactions were performed by photo-irradiation of TCE solutions containing an amine under O₂ bubbling over 70 °C with a low-pressure mercury lamp. TCE underwent photochemical oxidation to afford trichloroacetyl chloride having high toxicity and corrosivity, which then reacts in situ with the amine to afford NTCA. Compared with conventional NTCA synthesis with hexachloroacetone, the present reaction has the advantage of being widely applicable to a variety of amines, even those with low nucleophilicity such as amides, fluorinated amines, and amine HCl salts. NTCAs could be converted to the corresponding N-substituted ureas and carbamates through base-catalyzed condensation with amines and alcohols, respectively, with the elimination of CHCl₃. The reaction may proceed by the initial formation of isocyanate and its subsequent addition reaction with the amine or alcohol. This photochemical reaction also enables the synthesis of fluorinated NTCAs, which accelerate the reactions, and realizes the synthesis of novel fluorinated chemicals including polyurethanes.