An Efficient and Simple Synthesis of Functionalized and Unfunctionalized Enantiomerically Pure Diene-Iron Tricarbonyl Complexes

The esters of 2,4-alkadienoic acids with S-(-)-ethyl lactate, obtained either by direct esterification or via Horner-Emmons olefination with the optically active phosphonate 3 [ethyl 2-(diethoxyphosphorylacetoxy)propanoate], give diastereomeric diene-iron tricarbonyl complexes [tricarbonyl(1-ethoxycarbonyl-ethyl 2-5-η-alka-2,4-dienoate)iron]. These are easily separated by simple silica gel chromatography and readily transformed into the optically active diene complexes (methyl esters) 6 [tricarbonyl-(methyl 2-5-η-alka-2,4-dienoate)iron] and (unfunctionalized dienes) 7 [tricarbonyl(2-5-η-alka-2,4-diene)iron] both of high optical purity. The absolute configuration of a number of these complexes could be attributed on the basis of chemical correlations.