Novel Chiral Diamino-Oligothiophenes as Valuable Ligands in Pd-Catalyzed Allylic Alkylations. On the “Primary” Role of “Secondary” Interactions in Asymmetric Catalysis
A new class of chiral C2-symmetrical diamino-oligothiophenes is described to be effective in catalyzing Pd-mediated asymmetricallylicalkylations in a highly enantioselective manner. The combination of experimental as well as crystallographic evidence revealed the key role played by sulfur-based heteroaromatic rings in the stereodiscriminating step of the procedure. In particular, unprecedented non-covalent
Enantiomerically pure diamino-bis(tert-thiophene) 1b proved to be a valuable and flexible chiral ligand for Pd- and Zn-catalyzed transformations, allowing for high levels of stereocontrol in asymmetric allylic alkylation (ee up to 99%) and hydrosilylations of prochiral carbonyls (ee up to 97%).
N-Heterocyclic carbenes as ligands in palladium-catalyzed Tsuji–Trost allylic substitution
作者:Yoshihiro Sato、Taro Yoshino、Miwako Mori
DOI:10.1016/j.jorganchem.2005.07.043
日期:2005.12
reaction. Allylicsubstitutionusing a Pd–NHC complex differed from that using a Pd–phosphine complex as follows: (1) the reaction using a Pd–NHC complex required elevated temperature (50 °C or reflux in THF), (2) allylic carbonates were inert to a Pd–NHC complex, and (3) nitrogen nucleophiles such as sulfonamide and amine did not react with allylic acetate. It was also found that allylicsubstitution with
研究了使用N-杂环卡宾作为配体的Pd(0)催化的烯丙基取代(即Tsuji-Trost反应)。业已证明,在咪唑-2-亚烷基骨架中的氮原子上带有庞大的芳香环的咪唑鎓盐2d适合用作配体前体,并且Pd 2 dba 3-咪唑鎓盐2d -Cs 2 CO 3该系统对于在该反应中生产Pd-NHC催化剂非常有效。使用Pd-NHC络合物的烯丙基取代与使用Pd-膦络合物的烯丙基取代具有以下区别:(1)使用Pd-NHC络合物的反应需要升高的温度(50°C或在THF中回流),(2)烯丙基碳酸酯对Pd-NHC络合物呈惰性,并且(3)氮亲核试剂(如磺酰胺和胺)不会与乙酸烯丙酯反应。还发现使用Pd-NHC催化剂用软亲核试剂进行烯丙基取代是通过整体保留构型而进行的,从而以立体特异性方式得到产物,立体化学反应过程显然与使用Pd-膦的反应相同。复杂的。
π-Allylic Azidation in Water with an Amphiphilic Resin-Supported Palladium-Phosphine Complex
Ï-Allylic azidation of allyl esters was performed with an amphiphilic polystyrene-poly(ethylene glycol) (PS-PEG) resin-supported phosphine-palladium complex in water under heterogeneous conditions to give allyl azides in good to high yields. The polymeric palladium catalyst can be readily recovered and recycled.
Direct Copper‐Free Domino Conjugate Addition‐Cycloallylation using Organozinc Reagents
作者:Venukrishnan Komanduri、Fernando Pedraza、Michael J. Krische
DOI:10.1002/adsc.200800242
日期:2008.7.7
The Direct Approach: Enones possessing appendant allylic carbonates react directly with diorganozinc reagents in the presence of zinc diiodide [ZnI(2)] to provide 5- and 6-membered ring products of tandem or dominoconjugate addition-cycloallylation in good to excellent yield. In a related copper-free transformation, allylic carbonates are found to engage in direct allylic substitution with diorganozinc