1,141,772. 13 - Alkyl - gonahexaenes. H. SMITH. 25 May, 1966 [7 June, 1965 (2); 28 June, 1965], No. 23273/66. Addition to 1,116,810. Heading C2U. The invention comprises 17-alkoxy-13-alkylgona - 1,3,5(10),8,14,16 - hexaenes wherein the 13 - alkyl group contains at least 2 carbon atoms e.g. compounds of formula wherein R<;SP>;1<;/SP>; is an alkyl group having at least two carbon atoms, R<;SP>;2<;/SP>; is an etherified hydroxy group, R<;SP>;3<;/SP>; is an etherified hydroxy or acyloxy group, and each R is a hydrogen atom or an alkyl group, including both 13#- and 13α- enantiomers and racemates thereof, and their preparation by reaction of the corresponding 17 - keto - 1,3,5(10),8,14 - pentaene or 8 - seco - 14,17 diketo - 1,3,5(10),9(11) - tetraene with an alcohol under substantially anhydrous conditions. 13 - Alkyl -gona- 1,3,5(10),8-tetraenes wherein the 14 - hydrogen atom is transto the 13- alkyl group and the 17-substituent is cis to the 13-alkyl group are prepared by catalytic hydrogenation of the compounds of the invention. 13 - Alkyl - gona - 1,3,5(10) - trienes wherein the hydrogen atoms at the 8, 9 and 14 positions are transto the 13-alkyl group are prepared by catalytic hydrogenation either of the compounds of the invention or of the 1,3,5(10),8- tetraenes prepared therefrom.;/SP>;SP>;/SP>;SP>;/SP>;SP>