The present invention relates to compounds of formula (1). wherein: R1 is hydrogen atom or lower alkyl group, X is bromine atom or chlorine atom; and which are useful for the preparation of the cycloheptanoides such as cycloheptimidazole derivatives. The compound having formula (1) is obtained in a single pot by the reaction of a trialkylsilylether compound with a dihalocarbene which, in turn, is prepared from the reaction of chloroform or bromoform in the presence of base.