Synthese von optisch aktiven, natürlichen Carotinoiden und strukturell verwandten Naturprodukten. I. Synthese der chiralen Schlüsselverbindung (4<i>R</i>, 6<i>R</i>)‐4‐Hydroxy‐2,2,6‐trimethylcyclohexanon

Abstract

Synthesis of optically active natural carotenoids and structurally related compounds. I. Synthesis of the chiral key compound (4 R , 6 R )‐4‐hydroxy‐2,2,6‐trimethylcyclohexanone. A technical synthesis of (4 R , 6 R )‐4‐hydroxy‐2,2,6‐trimethylcyclohexanone ( 7 ) starting from the readily available oxo‐isophorone ( 2 ) is described. 7 is an ideal precursor for the synthesis of naturally occurring, optically active hydroxylated carotenoids ( e.g. zeaxanthin, cryptoxanthin and structurally related compounds). Chirality is introduced at C(6) by a stereoselective fermentative hydrogenation of the double bond using baker's yeast as the biocatalyst. Thereafter the carbonyl group at C(4) is reduced selectively and stereospecifically by chemical methods to the corresponding alcohol. Chemical reduction is preferably carried out by hydrogenation in the presence of a nickel catalyst or using triisobutylaluminium as the reducing agent. Stability, stereochemistry and physical properties of 7 and the stereoisomers thereof are discussed.