Structure of (+)-(3S,4R,5R,1'R,2'S,5'R)-tetracarbonyl{(3,4-η2)-5-[5'-methyl-2'-(1-methylethyl)cyclohexyloxy]-2(5H)-furanone}iron

Iron-Mediated Allylic Substitution Reactions with Chirality Transfer. Stereochemistry of the Formation of Diastereo- and Enantiomerically Enriched Olefinic and Allylic Tetracarbonyl Iron Complexes

“…A particularly characteristic feature is the upfield shift of the signals of the atoms at the β-position [⋮C(2)] of the alkenyl systems relative to those at the α-position [⋮C(1)] with respect to the acceptor group (SO 2 Ph or CO 2 Me) in comparison to the corresponding free alkenes ( S )- 6a − f and ( S )- 8 (Table ). For comparable cyclic tetracarbonyl(η 2 -alkene)iron(0) complexes possessing naturally a ( Z )-configured double bond this change is not observable. , The proton NMR spectroscopic observations are all in accordance with a partial “ferracyclopropane” substructure of the (η 2 -alkene)Fe(CO) 4 unit, allowing assignment of absolute configurations of the stereogenic centers at the complexed “olefinic” carbon atoms according to the Cahn−Ingold−Prelog notation (vide supra) 2 NMR Spectroscopic Details of Uncomplexed Ligands ( S )-6a/( S )-8 and Their Corresponding (η 2 -Alkene)tetracarbonyliron(0) Complexes 14a‘ / 14a‘ ‘ and 15‘/15‘ ‘ entrycompoundδ(Hα) [ppm]δ(Hβ) [ppm] 3 J trans [Hz]δ(Cα) [ppm]δ(Cβ) [ppm] 1 ( S )- 6a a 6.52 6.94 14.8 131.21 147.09 2 14a ‘ b 3.86 3.29 10.3 66.71 57.96 3 14a ‘ ‘ b 3.76 3.30 10.4 65.52 59.23 4 ( S )- 8 c 6.03 6.89 15.8 120.85 149.51 5 15 ‘ a 4.20 3.85 11.0 66.29 42.95 6 15 ‘ ‘ a 4.12 3.80 10.9 63.92 44.78 a 1 H NMR spectra recorded in C 6 D 6 at 300 MHz; 13 C NMR spectra recorded in C 6 D 6 at 75 MHz.…”

“…For comparable cyclic tetracarbonyl(η 2 -alkene)iron(0) complexes possessing naturally a (Z)-configured double bond this change is not observable. 23,43 The proton NMR spectroscopic observations are all in accordance with a partial "ferracyclopropane" substructure of the (η 2alkene)Fe(CO) 4 unit, allowing assignment of absolute configurations of the stereogenic centers at the complexed "olefinic" carbon atoms according to the Cahn-Ingold-Prelog notation (vide supra). 44 The CO ligands gave a single broad 13 C NMR resonance signal at δ ca.…”

“…In related cyclic systems the complexation seems kinetically to favor the sterically more hindered cis products (Ψ-endo, Figure 2). 23,43 Apparently, the observed trans selectivity (Ψ-exo, Figure 2) in the examples examined might be the result of thermodynamic equilibration.…”

“…In contrast, we and Speckamp et al described a slow isomerization of cyclic tetracarbonyl(η 2 -alkene)iron(0) complexes in dichloromethane. 23,43 Determination of the Molecular Structure of Complexes 14a′ and 14a′′ and Assignment of the Absolute Configurations of Complexes 14a-f and 15. Only few sulfonyl-substituted tetracarbonyl(η 2 -alkene)iron(0) complexes have been described in the literature so far.…”

“…Mixtures of (η 3 -allyl)tetracarbonyliron(1+) complexes 18′/′′ and 19′/′′ of different diastereomeric purity were chosen to react with an excess of two different test nucleophiles 20 and 21 (Scheme 6, Table 5). 43,55 The suspended cationic complexes gradually dissolve upon addition of the carbon nucleophiles to furnish initially the soluble intermediate neutral substituted (η 2 -alkene)tetracarbonyliron(0) complexes. Oxidative removal of the tetracarbonyliron moiety with ceric ammonium nitrate (CAN) (22) yielded the known 3-substituted alkenyl sulfone (R)-23 and 3-substituted ester (S)-24, which were isolated after workup and chromatographic purification in excellent to good yield (Table 5).…”