It is to be noted however that while such siloxa-cyclic compounds having the above formula wherein R is a methoxy or ethoxy radical, R' is methyl, X is a divalent alkylene radical selected from the group consisting of ##STR17## radicals and b has a value of 0 or 1 have been observed in the production of aldehyde-ethylene and aldehyde-propylene containing silane products, corresponding siloxa-cycli