Absolute configuration and circular dichroism of methyl substituted tricarbonyl(1,3-butadiene)iron(0) complexes

Abstract

Abstract The optically active methyl substituted tricarbonyl(1,3-butadiene)iron(0) complexes (2S,3R,4S)-(−)- 1 and (2R,3S,4R)-(+)- 2 have been synthesized by ionic hydrogenation with Et 3 SiH BF 3 from the acetate (−)-5 and from (+)-10 via (−)-9 in stereoselective reactions. The regioselectivity of the transformation leading from (−)-5 to 1 has been checked with deuterium labelled substrates 6, 7, and 8. An X-ray crystal structure of the (1S,4R)-camphanoate (−)-4 allowed the assignment of the absolute configurations of (−)-3, (−)-5 and hence of (−)-1. The stereoselective reduction of (2R,3R,4S)- 10 via 11 to 9 and the subsequent regioselective isomerization allowed the assignment of absolute configuration to (+)-2. The chiroptical properties of (+)-1 and (+)-2 were determined and compared with those of (2S,3R)-(+)-tricarbonyl(isoprene)iron(0) [(+)-12].