A convenient one-pot procedure for the mechanochemical nanocellulose-supported synthesis of trifluoromethyl arenes has been developed through the selective transformation of an aromatic amino group into the trifluoromethyl functionality using pyrylium tetrafluoroborate (Pyry-BF4) and trifluoromethyltrimethylsilane (TMSCF3) via in situ formation of the pyridinium salt intermediate under transition metal-free conditions. The nanocellulose acts here as a green reaction medium, and the reaction does not occur without this additive. The scope of the present protocol includes synthesis of 28 trifluoromethyl arenes in excellent yields via a selective (ipso-)substitution (SNAr) of aromatic amino group with CF3 functionality. This method could have a great significance in pharmaceutical industries for the late-stage functionalization of active pharmaceutical ingredients (APIs)/drugs.