Synthesis of cyclopropanes via organoiron methodology: preparation of 2-(2′-carboxy-3′-ethylcyclopropyl)glycine
A route to 1,2,3-trisubstituted cyclopropanes has been developed. The relative stereochemistry at the three cyclopropane centers is established by nucleophilic attack on the pentadienyl ligand on the face opposite to iron and subsequent oxidatively induced reductive elimination with retention of configuration. This methodology was applied to the synthesis of 2-(2′-carboxy-3′-ethylcyclopropyl)glycines. The diastereomeric glycine dimethyl esters are separable as their diphenylmethylene imines.
The conformationally restricted glutamate analogs (2S,1′S,2′S,3′R)- and (2R,1′S,2′S,3′R)-ECCG's 5a and5b were prepared in five steps (17 and 15% yield, respectively) from (pentadienyl)Fe(CO)3+ (1R)-6.