Zeolite encapsulated host–guest complexes [CuL(NO3)@Y], and [CuL2@Y] (where, HL is 3-[(3-dimethylamino-2,2-dimethyl-propylimino)-methyl]-naphthalen-2-ol) have been synthesized and characterized by XRD, FTIR, Raman, TEM, XPS, UV-DRS, BET, EXAFS, and EPR spectroscopy. These complexes used as heterogeneous catalysts for the oxidation of thioanisole, diphenyl sulfide, and 2-phenyl thioanisole to produce its sulfoxides analogues·H2O2 shows superior conversion efficiency and product selectivity over other common oxidants, viz tert-butyl hydroperoxide (TBHP), urea hydrogen peroxide (UHP) and di-tert-butyl hydroperoxide (DTBP). Formation of thermally stable copper hydroperoxo intermediate, which is to be believed as rate determining step in past few years, has been well proven. Besides that, for the first time, we have established that the oxidation process is not only going through by the generation of Cu(II)–OOH species but there is a considerable role of electron transfer (ET) mechanism also. Further, better TON value and recyclability make the encapsuled heterogeneous complexes more useful than that of homogeneous analogues. © 2020 Elsevier Inc.