Asyreaetric coordination of prochiral 1,3-dienes to form optically active (dienejFe(CC03 complexes has been achieved by direct transfer of the Fe02012 group from chiral enone complexes. Complexation of an unsymmetrically substituted 1,3-diene produces a chiral molecule, with one face of the diene distinguished by bonding to the metal. Were we report a complexation process which enables the two faces of a prochiral diene to be differentiated for the first time, resulting in the production of optically active tricarbonyliron complexes. Various a,B-unsaturated ketones, which form moderately stable tricarbonyliron complexes, are known to act as a convenient source of an iron carbonyl moiety for transfer to 1,3-dienes.l Analogous transfer reagents prepared simply from two readily available chiral enones, (+)-pulegone (I) and (-)-3B-acetyloxypregna-5,16-diene-lo-one (II), (16-DHA) were used without isolation to provide a direct synthesis of optically active complexes of 1-methoxycyclohexa-1,3-diene (III), 1-methoxy-4-methylcyclohexa-1,3-diene (IV) and methyl sorbate (V), as shown in the Table.
Complexes of pulegone3 were prepared thermally from Fe2(CO)S (light petroleum, b.p. 40-60ยฐ, 5 hrs). After filtration through celite , evaporation of solvent and Fe(C0)5, addition of the 1,3-diene in degassed benzene, toluene or light petroleum (b.p. 40-60') and heating at reflux for the appropriate time, the crude product was distilled and chromatographed on silica gel. The compounds were distilled a second time and optical rotations measured on analytically pure samples. A similar method was used for 3@acetyloxypregna-5,16-diene-ZO-one, except that crystallisation of the crude product from hexane resulted in