A novel process for the preparation of 1'-hydroxy-2'-substituted cyclohexyl azetidin-2- one compound of formula 2, which is important intermediate in the synthesis of trinems, is described by epoxide ring opening of (3S,4R)-3-[(1R)-1-(tert- butyldimethylsilyloxy)ethyl]-4-[(1'R,2'S,3'R)-1',2'-epoxycyclohexan-3'-yl]azetidin-2-one of formula 1 with the nucleophile compound of formula RYH, where nucleophile may act as solvent itself if the nucleophile is in the liquid form, in a suitable solvent and in the presence of a suitable catalyst from the group of salt of trifluoromethane sulfonic acid, preferably ytterbium (III) trifluoromethanesulfonate, stannous (II) trifluoromethanesulfonate or dysprosium (III) trifluoromethanesulfonate, under a) ultrasonic irradiation or b) under microwave irradiation of the reaction mixture following by isolation and purification of the desired compound. A variant of the novel process describes ring epoxide opening of the starting compound of formula 1 with the compound of formula NH 4 X in a suitable solvent under a) microwave irradiation or b) without microwave irradiation to obtain the desired compound of formula 2. Instead of compound of formula 1 a compound of formula 6 may be used as starting compound where any other suitable hydroxy protecting group known in the art may be used in the formula of the starting compound.