Abstract: Preparing (3R, 3'R)-zeaxanthin of the formula I ##STR1## starting from (4-hydroxy-2,2,6-trimethylcyclohexanone of the formula II ##STR2## via the novel intermediates (4R,6R)-1-formyl-2,2,6-trimethyl-7-oxabicyclo[2.2.1]heptane of the formula IV ##STR3## (4R,6R)-1-(3-oxo-1-butenyl)-2,2,6-trimethyl-7-oxabicyclo[2.2.1]heptane of the formula V ##STR4## (4R,6R)-1-(3- hydroxy-3-methyl-1,4-pentadienyl)-2,2,6-trimethyl-7-oxabicyclo[2.2.1]heptan e of the formula VI ##STR5## [5-(4R,6R)-(4-hydr oxy-2,2,6-trimethyl-1-cyclohexylidene)-3-methyl-1,3-pentadienyl]triarylphos phonium salt of the formula iso-III ##STR6## where Ar is aryl and X is one equivalent of an anion of a strong acid. The (4R,6R)-1-formyl-2,2,6-trimethyl-7-oxabicyclo[2.2.1]heptane of formula IV is obtained by reacting the ketone of the formula II with dichloromethyllithium, which can be prepared by metallation of dichloromethane with butyllithium or lithium diisopropylamide.

Abstract: A process for the preparation of pure trans- and cis-4-hydroxy-2, 2,6-trimethylcyclohexan-1-one from a mixture of these isomers comprises fractionally rectifying the isomeric mixture in a suitable column having from about 30 to 80 theoretical separation stages at temperatures of preferably from 50.degree. to 130.degree. C. and a pressure in the range from 0.1 to 5 mbar. The products are essential intermediates for the preparation of 3-hydroxycarotenoids such as cryptoxanthin and zeaxanthin.