Process for the preparation of unsaturated aldehydes

Claim 1

A process for the preparation of α-sinensal which comprises: a. brominating 3-methyl-penta-2,4-dienol, b. reacting the obtained 3-methyl-penta-2,4-dien-1-yl bromide with mesityloxide at a temperature of from about -70°C to about -30°C in the presence of an alkali metal hydride or alkali metal amine, c. reacting the obtained 3-isopropenyl-6-methyl-octa-5,7-dien-2-one with vinyl-magnesium bromide, d. brominating the thus obtained 3,7-dimethyl-4-isopropenyl-3-nona-1,6,8-trien-3-ol at a temperature from about -5°C to about +20°C and in the presence of an inert organic solvent e. treating the 3,7-dimethyl-4-isopropenyl-nona-2,6,8-trien-1-yl bromide obtained with an amino-cyanide of formula ##EQU1## wherein each one of the symbols R 4 and R 5 , identical or different, represents a lower alkyl radical, or R 4 together with R 5 and the nitrogen atom may constitute a heterocycloaliphatic ring as indicated by the dotted line, and subsequently adding to the reaction mixture a strong basic agent selected from the group consisting of potassium tert-butoxide, sodium ethoxide, potassium methoxide and potassium ethoxide, f. converting the amino-nitrile obtained into 2,6-dimethyl-2-vinyl-3-isopropenyl-octa-5,7-dienal by treating it with a basic or a neutral reagent selected from the group consisting of alkali metal alkoxides or hydroxides and cyanide complexation agents, and in the presence of an inert organic solvent, and g. thermally treating said aldehyde at a temperature above about 100°C in the presence of a basic or a neutral agent selected from the group consisting of an alkali metal salt, a strong base anion exchange resin and a tertiary amine in an inert organic solvent.