A process for preparing a silane of the formula I R.sup.1.sub.n SiR.sup.2.sub.m (I) where R.sup.1 is --O--Y, n is an integer from 1 to 3, R.sup.2 is ##STR1## m is an integer from 1 to 3 and n+m=4, and Y and Z are each, independently of one another, unsubstituted or mono- or polyhalo-substituted C.sub.1 --C.sub.20 -alkyl, C.sub.2 --C.sub.20 -alkenyl, C.sub.2 --C.sub.20 -alkynyl and --(CH.sub.2).sub.p --A, where p is an integer from 0 to 6 and A, which is unsubstituted or substituted by one or more C.sub.1 -C.sub.6 -alkyls, is a 3- to 20-membered hydrocarbon ring entails reacting a halosilicon compound of the formula II SiX.sub.4 (II) where X is fluorine, chlorine, bromine and iodine, with compounds of the formula III and IV, or with an anhydride of the formula V and the compound of the formula IV ##STR2## where R.sup.1 and R.sup.2, and Z have the above meanings, M is a metal of main group one and two.