Odorants and compositions comprising odorants

A process for the preparation of ketones selected from compounds of formula (5) or of formula (6)

• wherein R is an alkyl group having from 1 to 9 carbon atoms, an alkenyl group containing only one carbon-carbon double bond and having up to 9 carbon atoms, an (substituted) aryl group having up to 9 carbon atoms, an oxo-alkyl group having up to 9 carbon atoms, an alkoxyaryl group containing up to 9 carbon atoms or a (substituted) benzyl group having up to 9 carbon atoms,
• wherein the compounds of Formula (5) are prepared by subjecting 2,3-dimethylbutene(s) to an acylation reaction step in the presence of a Brønsted acid catalyst, optionally followed by either an alkylation or an aldol condensation step, to form the compounds of Formula (5), and/or
• wherein the compounds of Formula (6) are prepared by subjecting 2,3-dimethylbutene(s) to an acylation reaction step in the presence of a Brønsted acid catalyst, optionally followed by either an alkylation or an aldol condensation step, to form the compounds of Formula (5) and by subjecting the said compounds of Formula (5) to a hydrogenation reaction step to form the compounds of Formula (6).