A practical asymmetric 1,2‐addition of functionalised arylzinc halides to aromatic and aliphatic aldehydes is described by the use of aminoalcohol catalysis in the presence of AlMe3. The process is simple to carry out, uses only commercially available reagents/ligands and provides moderate to good (80–96 % ee) enantioselectivities for a wide range of substrates. Either commercial ArZnX reagents or those prepared in situ from low cost aryl bromides can be used. In the latter case electrophilic functional groups are tolerated (CO2Et, CN). The reaction relies on rapid exchange between ArZnX and AlMe3 to generate mixed organometallic species that lead to the formation of a key intermediate that is distinctly different from the classic “anti” transition states of Noyori. NMR monitoring and related experiments have been used to probe the validity of the proposed selective transition state. 相似文献
The copper‐catalysed conjugate addition of trialkylaluminium and dialkylzinc reagents to polyconjugated nitroolefins (nitrodiene and nitroenyne derivatives) is reported. A reversed Josiphos ligand L7 allows for the selective 1,4‐ or 1,6‐addition with high enantioselectivities. 相似文献
A new type of axially chiral cyclo‐[1,1′‐biphenyl]‐2,2′‐diol (CYCNOL) ligands with adjustable dihedral angles have been developed by varying the bridge chain length. Eight‐, nine‐ and ten‐membered cyclo‐ligands were prepared and evaluated by using two representative examples: enantioselective additions of diethylzinc to aldehydes and organometallic reagents to enones. The results revealed that the fine regulation of dihedral angles through variation of the bridge chain length was effective in the asymmetric synthesis. 相似文献
Asymmetric catalysis under almost‐neutral reaction conditions is key for the efficient synthesis of optically active polar molecules. We have developed catalytic enantioselective reactions of acyclic or cyclic alkenyl esters by using an (S)‐BINOL‐derived chiral tin‐dibromide reagent that possesses a bulky aryl group at the 3 or 3′ position as the chiral pre‐catalyst in the presence of a sodium alkoxide and an alcohol, in which a chiral tin alkoxide bromide is generated in situ and recycled with the assistance of an alcohol. In this Personal Account, we describe three types of asymmetric transformation that proceed through a chiral tin enolate: 1) The asymmetric aldol reaction of alkenyl esters or unsaturated lactones with aldehydes or isatins; 2) the asymmetric three‐component Mannich‐type reaction of alkenyl esters and related cycloaddition reactions; and 3) the asymmetric N‐nitroso aldol reaction of unsaturated lactones with nitrosoarenes. 相似文献
Green carbanion surrogates : Organotrialkylsilanes occupy a niche in the array of ‘green’ carbon nucleophiles open to chemists that few other reagents can fill. Despite being known for over 30 years, it is only recently that their true worth in stereoselective carbonyl addition and related processes has started to emerge, primarily due to their low reactivity. It is our hope that this minireview will make the true worth of these reagents more widely known, setting the stage for expanded usage of these versatile yet benign reagents in organic synthesis.
Phosphine oxides and spirocyclic compounds are privileged molecules widely employed in a variety of catalytic transformations either as chiral ligands for metals or bifunctional organocatalysts. Herein, we developed a Pd-catalysed cross-coupling reaction to synthesize spirocyclic amino-phosphine oxides with a P-stereogenic centre which could serve as potential P*(O), N-ligands or organocatalysis. 相似文献
The reactions of [Co2(CO)8] with one equiv of the benzamidinate (R2bzam) group‐14 tetrylenes [M(R2bzam)(HMDS)] (HMDS=N(SiMe3)2; 1 : M=Ge, R=iPr; 2 : M=Si, R=tBu; 3 : M=Ge, R=tBu) at 20 °C led to the monosubstituted complexes [Co2{κ1M?M(R2bzam)(HMDS)}(CO)7] ( 4 : M=Ge, R=iPr; 5 : M=Si, R=tBu; 6 : M=Ge, R=tBu), which contain a terminal κ1M–tetrylene ligand. Whereas the Co2Si and Co2Ge tert‐butyl derivatives 5 and 6 are stable at 20 °C, the Co2Ge isopropyl derivative 4 evolved to the ligand‐bridged derivative [Co2{μ‐κ2Ge,N‐Ge(iPr2bzam)(HMDS)}(μ‐CO)(CO)5] ( 7 ), in which the Ge atom spans the Co?Co bond and one arm of the amidinate fragment is attached to a Co atom. The mechanism of this reaction has been modeled with the help of DFT calculations, which have also demonstrated that the transformation of amidinate‐tetrylene ligands on the dicobalt framework is negligibly influenced by the nature of the group‐14 metal atom (Si or Ge) but is strongly dependent upon the volume of the amidinate N?R groups. The disubstituted derivatives [Co2{κ1M?M(R2bzam)(HMDS)}2(CO)6] ( 8 : M=Ge, R=iPr; 9 : M=Si, R=tBu; 10 : M=Ge, R=tBu), which contain two terminal κ1M–tetrylene ligands, have been prepared by treating [Co2(CO)8] with two equiv of 1 – 3 at 20 °C. The IR spectra of 8 – 10 have shown that the basicity of germylenes 1 and 3 is very high (comparable to that of trialkylphosphanes and 1,3‐diarylimidazol‐2‐ylidenes), whereas that of silylene 2 is even higher. 相似文献
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