A New Approach to Diastereoselective and Enantioselective Cyclopropane Syntheses Using the Chiral Iron Carbene Complexes S - and R -[(η 5 -C 5 H 5 )(CO) 2 Fe CH[(η 6 - o -CH 3 OC 6 H 4 )Cr(CO) 3 ]] +

Study of the origin of enantioselectivity in cyclopropanation reactions using the chiral iron carbene complex [(η5-C5H5)(CO)2FeCH[(η6-o-MeOC6H4)Cr(CO)3]]+

“…However, in the case of 3, the obtained ee values clearly do not reflect the initial syn/anti ratio which would induce only an ee of only 29%, independent of the nature of the olefin employed. The experimentally determined ee values are considerably higher, namely 46-65% for monosubstituted olefins and up to 95% for disubstituted olefins [7,9]. This is a clear indication that it is not only the abundance of syn and anti carbene isomers, but also other factors like their relative reactivities, that determine the selectivity of the reaction.…”

“…In a similar manner, anti R-3 may induce S-configuration through frontside closure or R-configuration through backside closure (Scheme 5). We previously have shown by crystallography that reaction of the R-isomer of 3 with 2-methyl-propene induces predominantly an R-configuration at C-1 of the resulting cyclopropane (RR-(À)-2,2 dimethyl-1-o-methoxyphenyl(tricarbonyl chromium)cyclopropane; whereas the S-carbene results in the corresponding SS isomer [7,8].…”

“…This carbene complex is prepared in situ from the precursor Cp(CO) 2 Fe@CH(OSiMe 3 )[g 6 -(o-MeOC 6 H 4 )Cr(CO) 3 ] by addition of Me 3 SiSO 3 CF 3 (trimethylsilyl triflate) at À78°C. Reaction with disubstituted olefins resulted in ee values as high as 95% [7]. While reaction with monosubstituted olefins like styrene yielded mainly cis-cyclopropanes, the ee values were considerably lower (46-60%) [8] (Table 1).…”

Recent chemistry of the η5-cyclopentadienyl dicarbonyl iron anion

“…A hallmark of the Hossain procedure uses the aforementioned ClSiMe 3 to trap the resultant alkoxide complex followed by addition of TMSOTf in situ to generate the cationic Fp + carbene. Their method has been employed toward the synthesis of enantiospecific cyclopropanes Scheme using Fp anion addition to various chiral 6 -Cr(CO) 3 aryl aldehydes [12,[238][239][240][241]. This asymmetric method has resulted in various chiral cis cyclopropanes in high ee and overall yield.…”

Beyond Directed Ortho Metalation: Ruthenium-Catalyzed Amide-Directed CAr–N Activation/C–C Coupling Reaction of Anthranilamides with Organoboronates

“… a Yields are of isolated and purified products. b Equivalents of boroneopentylates/reaction times in hours are shown in parentheses. c 10 mol % catalyst loading. d cis or trans stereochemistry not established by 1 H NMR due to almost identical J cis and J trans coupling constants and unavailability of crystalline material for X-ray analysis. …”