4,5-Didehydro-9-demethyl-9-halo-5,6-dihydroretinals and Their 9-Cyclopropyl and 9-Isopropyl Derivatives - Simple Preparation of α-Ionone Derivatives and Pure (all-E)-, (9Z)- and (11Z)-α-Retinals

摘要

-Ionone and several of its chemically modified derivatives have been prepared in high yield in full isomeric purity by a Wadsworth-Emmons procedure using imino-phosphonate anion reagents. Starting from α-ionone, 5-(2,6,6-trimethylcyclo-2-hexen-1-yl)-4-penten-2-yn-1-al could be prepared in a high yielding one-pot procedure. The corresponding (9-Cl-, 9-Br- and 9-I-α-ionylidene)acetaldehyde system could be obtained in one step in a quantitative mixture of (9Z) and (all-E) isomers by 1,4-nucleophilic addition reactions. The pure (all-E) and (9Z) isomers could be separated by simple column chromatography. The corresponding [(9Z)- and (all-E)-9-demethyl-9-fluoro-α-ionylidene]acetaldehydes could also be obtained in pure form by simple column chromatography. These α-ionylidene systems could be easily converted either into the (all-E)-4,5-didehydro-9-demethyl-9-halo-5,6-dihydroretinals or the corresponding (9Z) isomers in two steps. Similar mixtures of the corresponding (9Z,11Z)- and (9Z)-nitriles could be obtained by normal chemistry. The (9Z,11Z) isomer is the main component of this mixture, and could be obtained in pure form. Subsequent reduction with DIBAL-H and careful workup gave the pure (9Z,11Z)-9-haloretinals. These (9Z,11Z) isomers show a similar extreme acid sensitivity to the corresponding 9-halo-β-retinals. α-Retinal and its 9-demethyl, 19,19-ethano and 19,19-dimethyl derivatives have been prepared in the (all-E), (9Z), and (11Z) isomeric forms in a similar manner. The corresponding β-retinal and its 9-demethyl derivative in the various isomeric forms are known. In this paper the 19,19-ethano- and 19,19-dimethyl-β-retinals in the (all-E), (9Z), and (11Z) isomeric forms are also reported.