Extension of an aliphatic chain by five, six, or seven carbon atoms may be achieved by adding to it a 5-, 6-, or 7-membered olefmic alicycle and subsequently breaking the double bond. Addition of the ring is achieved by a Grignard reaction between an alkylmagnesium bromide and a cyclic ketone, and the resulting 1-alkylcycloolefin is opened by ozonolysis. The end product is a 5-, 6-, or 7-keto acid.