Acyliron complexes with central chirality at the metal are obtained by substitution
of a carbon monoxide with a phosphine ligand. Kinetic resolution of the racemic
acyliron complex can be achieved by aldol reaction with (1R)-(þ)-camphor
(Scheme 1.14) [41]. Along with the enantiopure (RFe)-acyliron complex, the (SFe)-
acyliron–camphor adduct is formed, which on treatment with base (NaH or NaOMe)
is converted to the initial (SFe)-acyliron complex. Enantiopure acyliron complexes
represent excellent chiral auxiliaries, which by reaction of the acyliron enolates with
electrophiles provide high asymmetric inductions due to the proximity of the chiral
metal center. Finally, demetallation releases the enantiopure organic products.
a,b-Unsaturated acyliron complexes are versatile reagents and show high stereoselectivity
in many reactions, e.g. as dienophiles in Diels–Alder reactions [42], as
Michael acceptors for heteronucleophiles [43] and in [3þ2]-cycloadditions with
allyltributylstannane to cyclopentanes [44].
Fp-substituted enones and enals undergo cyclocarbonylations on treatment with
metal hydrides or metal alkyls to provide g-lactones (Scheme 1.15) [45]. Similarly,
electron-rich primary amines afford dihydropyrrolones with iron-substituted (Z)-
enals in the presence of titanium tetrachloride and triethylamine [46].