A process of preparing a compound of formula (I) ##STR00001## wherein R represents a linear or branched C5 alkyl group, as well as the use of such compounds in a fragrant and/or flavouring composition.

The invention relates to a compound of general formula (I) wherein: A) a) R.sub.4, R.sub.5, and R.sub.7 each represent a hydrogen atom and R.sub.3, R.sub.6 and R.sub.8 each represent a methyl radical, or b) R.sub.4, R.sub.6, and R.sub.7 each represent a hydrogen atom and R.sub.3, R.sub.5 and R.sub.8 each represent a methyl radical, or c) R.sub.3, R.sub.6 and R.sub.7 each represent a hydrogen atom and R.sub.4, R.sub.5 and R.sub.8 each represent a methyl radical, and the dotted lines are present and represent cis-double bonds or trans-double bonds, and R.sub.1 represents a hydrogen atom and R.sub.2 represents an OH, OCH.sub.3 or OC.sub.2H.sub.5 group, or the dotted lines are absent and R.sub.1 represents a hydrogen atom and R.sub.2 represents an OCH.sub.3 group or an OC.sub.2H.sub.5 group; or B) R.sub.1, R.sub.4, and R.sub.6 each represent a hydrogen atom and R.sub.2, R.sub.3 and R.sub.5 each represent a methyl radical, and the dotted lines are present and represent cis-double bonds or trans-double bonds, and R.sub.7 represents a hydrogen atom and R.sub.8 represents an OH, OCH.sub.3 or OC.sub.2H.sub.5 bond, or the dotted lines are absent and R.sub.7 represents a hydrogen atom and R.sub.8 represents an OCH.sub.3 group or an OC.sub.2H.sub.5 group. The inventive compound is an alcoholic derivative or an ether derivative. The invention also relates to the use of at least one compound of formula (I) as an odorant agent.

The invention relates to a gamma-undecenolactone of formula (I), wherein a lactonic cycle can carry an unsaturation between carbon N.sup.o2 and carbon N.sup.o3 and is preferably saturated, RI is a possibly substituted C.sub.7 alkenyl or alkynyl group comprising at least one unsaturation, and preferably RI is an CH.sub.2.dbd.CH--CH.sub.2--CH.sub.2--CH.sub.2--CH.sub.2--CH.sub.2 group, said gamma-undecenolactone contains an asymmetric carbon in position 4 having (R) or (S) configuration. The biosynthesis of said gamma-undecenolactone and the use thereon for perfumery and for a food flavouring agent are also disclosed.

A compound of general formula (I) with or without the double bond illustrated by the dotted line. In formula (I), X is a CHO, CH2OH, CH2OC(O)R or CH(OR)2 group, and R represents a linear or branched C1-C5 alkyl or alkenyl chain. The synthesis method for the compound, and especially the 6,8-dimethyl-non-7-enal (1) prepared by the hydroformylation of the 5,7-dimethyl-octa-1,6-diene is also disclosed, as well as compositions containing the compounds of formula (I). Due to the odorant properties thereof, the compounds are highly useful in perfumery, especially for cosmetic products and household products.

Method for stereoselectively preparing a (R) or (S) gamma-lactone consists in microbially biosynthesising gamma-lactone, wherein the biosynthesis is carried out from a substrate selected from C5 to C20 fatty acids with the aid of a strain selected from those enabling a stereoselective hydroxylation in C4 of the substrate, in particular Aspergollus sp or Mortierella sp. The biosynthesis of the gamma-lactone and the use thereof in perfumery and for food flavouring agents are also disclosed.