Approaches to enantioselective syntheses using tricarbonyl(diene)iron complexes

Abstract

Staffordshire ST5 5BGMethods for the resolution of tricarbonyl( 1 -5-q-cyclohexadienyl) iron salts are described involving the separation of diastereoisomeric pairs obtained by nucleophilic attack using chiral phosphines, alkoxides, and amines. Nucleophilic attack by CN-on [Fe(q5-C,H,) (CO)2L'J BF4 to give [Fe(C6H7CN-exo-5) (CO),L*] [L' = (+)-neomenthyldiphenylphosphine] proceeds with significant asymmetric induction at the chiral carbon so formed.

Reactivity of (Bicyclo[5.1.0]octadienyl)iron(1+) Cations: Application to the Synthesis of cis-2-(2‘-Carboxycyclopropyl)glycines

“…Alternatively, Howell has reported diastereoselective addition of cyanide anion to a (cyclohexadienyl)iron(1+) cation bearing a chiral phosphine ligand (ca. 2:1 dr) . To this end, 4 readily underwent ligand substitution with ( S )-neomenthyldiphenylphosphine [NMDPP] in the presence of trimethylamine N -oxide [TMANO] to give phosphine-ligated (−)- 24 in high yield (Scheme ).…”

Synthetic applications of cationic iron and cobalt carbonyl complexes

“…43 An alternative method for resolution involves the treatment of a racemic cationic iron carbonyl dienyl complex with a chiral alcohol such as (-)-menthol, providing diastereomeric products that are separable by chromatography. 20 Subsequent regeneration of the cation by treatment with strong acid then gives access to both the enantiomeric forms of the cationic complex. Enantioenriched complexes can also be prepared by other means.…”

New chemical and stereochemical applications of organoiron complexes

“…Transfer of the carbene ligand from optically active transition-metal-carbene complexes to alkenes represents a potentially useful and general method for the enantioselective synthesis of cyclopropanes [ 224 ], and this task was successfully accomplished by the Brookhart group [ 225 ]. The starting complexes were obtained as a pair of iron acyl diastereoisomers, e.g., 58 (2SS) and 59 (2RS), differing in configuration at iron.…”

“…A study [ 225 ] discussed at length the role of the metal (e.g., iron) vs. ligand chirality in the optical induction. With iron-ethylidene complexes having a chiral phosphine in place of one CO ligand, high asymmetry induction was expected (and observed) [ 224 ].…”