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

Abstract

The preparation of highly diastereo- and enantiomerically enriched alkoxycarbonyl-substituted tetracarbonyl (η 3-allyl)iron(1+) complexes 2a–d ( 2a–c: 20–53%, de > 90- ⩾ 95% or greater; 2d: 31–40%, ee ⩾ 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- ⩾ 95% ( 4a–f) or ee ⩾ 96- ⩾ 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.