NOVEL METHOD FOR A STEREOSELECTIVE SYNTHESIS OF TRISUBSTITUTED OLEFINUSING TRICARBONYLIRON COMPLEX - A HIGHLY STEREOSELECTIVE SYNTHESIS OF(ALL-E)-RETINOIC AND (9Z)-RETINOIC ACIDS

In order to establish the stereoselective synthesis of retinoic acids, which are ligand molecules of the retinoic acid receptors (RARs, all- E-isomer) and the retinoid X receptors (RXRs, 9Z-isomer), the reaction of beta-ionone-tricarbonyliron complex 7 with carbanions was investig ated. Treatment of 7 with the lithium salt of acetonitrile afforded 7E ,9E)-beta-ionylideneacetonitrile-tricarbonyliron complex 8 exclusively , via addition, dehydration, and migration of tricarbonyliron complex. On the contrary, the reaction of 7 with the lithium enolate of ethyl acetate and subsequent dehydration by thionyl chloride afforded the et hyl (7E,9Z)-beta-ionylideneacetate-tricarbonyliron complex 16b predomi nantly. These compounds (8 and 16b) were converted to the correspondin g beta-ionylideneacetaldehyde-tricarbonyliron complexes (10 and 22) in excellent yields, respectively. The Emmons-Horner reaction of these c ompounds with C5-phosphonate followed by the sequence of decomplexatio n and alkaline hydrolysis gave the corresponding retinoic acids (26 an d 29).