排序方式: 共有30条查询结果,搜索用时 15 毫秒
21.
Johnson JB Bercot EA Rowley JM Coates GW Rovis T 《Journal of the American Chemical Society》2007,129(9):2718-2725
Results from a mechanistic study on the Ni(COD)2-bipy-catalyzed alkylation of anhydrides are consistent with turnover-limiting reductive elimination at high Et2Zn concentrations. While the presence of styrene does not affect the initial rate of alkylation, it appears to inhibit catalyst decomposition and provides higher product yield at long reaction times. In contrast, Ni(COD)2-iPrPHOX-catalyzed anhydride alkylation proceeds through two competing catalytic cycles differentiated by the presence of styrene. The presence of styrene in this system appears to accelerate rate-limiting oxidative addition and promotes the cycle which proceeds 4 times more rapidly and with much higher enantioselectivity than its styrene-lacking counterpart. 相似文献
22.
23.
24.
Substituted succinic and glutaric anhydrides undergo a nickel-catalyzed monofunctionalization with organozinc reagents as nucleophiles. The reaction proceeds readily with a variety of substrates, employs commercially available or readily attainable reagents, tolerates sensitive functionality on both partners, and affords the product ketoacids in moderate to high yields. The use of a chiral phosphinooxazoline results in a desymmetrization of a meso anhydride to provide the ketoacid in 85% yield and 79% ee. 相似文献
25.
Monoalkylation of cyclic anhydrides provides an opportunity to couple a carbon-carbon bond-forming event with the control of backbone stereochemistry. We have developed a palladium-JOSIPHOS catalyst system that desymmetrizes meso-succinic anhydrides using organozinc reagents as nucleophiles, and have found that, in many cases, this reaction proceeds at ambient temperature. 相似文献
26.
27.
28.
Treatment of cyclic anhydrides with stoichiometric amounts of nickel-neocuproine complex generates alkylcarboxylato-nickelalactones upon extrusion of CO. These metalacycles undergo cross-coupling with arylzinc reagents. The generated CO is sequestered in situ by a nickel-dppb complex. The overall sequence effects a secondary sp3(electrophile)-sp2(nucleophile) cross-coupling and allows for control of stereochemistry during the bond-forming event. 相似文献
29.
Two new methods for the synthesis of 2-aminothiazolones from 2-(4-methoxybenzylthio)acetic acids are described. A single reagent and simple experimental conditions are used in the key tandem deprotection-cyclization process. In the first approach 2-aminothiazolones are directly accessed via cyclization of the corresponding N-acylisothioureas. The second complementary approach provides access to a variety of 2-thiomethylthiazolones via cyclization of N-acyldithioimidates. The product 2-thiomethylthiazolones are then efficiently converted to 2-aminothiazolones via amine displacement. 相似文献
30.
The use of mixed zinc reagents in Ni-catalyzed anhydride alkylation results in preferential transfer of substituents (Ph > Me > Et > iPr approximately TMSCH2) for the ligands bipy, dppe, and iPrPHOX. Utilization of such mixed species allows the use of 0.55 equiv of the diorganozinc reagent, effectively transferring both desired substituents when used in conjunction with a suitable second zinc reagent. 相似文献