Synthesis of highly diastereo- and enantiomerically enriched tetracarbonyl(eta(3)-allyl)iron(1+) complexes for allylic substitutions with silyl enol ethers and silyl ketene acetals

The preparation of highly diastereo- and enantiomerically enriched alkoxycarbonyl-substituted tetracarbonyl(eta(3)-allyl)iron(1+) complexes 2a-d (2a-c: 20-53%, de > 90- greater than or equal to 95% or greater; 2d: 31-40%, ee greater than or equal to 99%) by means of an auxiliary controlled complexation (aux. = 8-phenylmenthyl) of diastereo- or of enantiopure (E)-configuration enoates 1 as starting materials is reported. The nucleophilic addition of various silyl enol ethers or silyl ketene acetals 3a-e to the complexes 2a-d followed by oxidative cleavage of the carbonyliron fragment offers an efficient access to 6-oxoenoates 4 in moderate to excellent yields (five steps, 5-72%) with diastereomeric or enantiomeric excesses ranging from de > 90- greater than or equal to 95% (4a-f) or ee greater than or equal to 96- greater than or equal to 99% (4g-k) with retention of the (E)-double bond geometry. The reaction proceeds with virtually complete chirality transfer from C-O via C-Fe to C-C with retention (double inversion) of stereochemistry of the stereogenic centre with respect to the starting material 1. It has been proven that a uniform configuration of the carbon atom bearing the leaving group in 1 is essential for controlling the absolute stereochemistry during the formation of complexes of type 2 with a definite absolute configuration at the allylic position.