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61.
Mechanism of Phosphine‐Catalyzed Allene Coupling Reactions: Advances in Theoretical Investigations 下载免费PDF全文
Dr. Cheng‐Xing Cui Dr. Chunhui Shan Prof. Yu‐Ping Zhang Prof. Xiao‐Lan Chen Prof. Ling‐Bo Qu Prof. Yu Lan 《化学:亚洲杂志》2018,13(9):1076-1088
Organocatalysis has emerged as an effective strategy for chemical synthesis. Within this area, phosphine‐catalyzed coupling reactions have attracted considerable attention because of their versatility and wide range of applications in the construction of new C?C bonds. Recently, various experimental studies on the phosphine‐catalyzed coupling reaction of allenes have been reported, and mechanistic and computational studies have also progressed considerably. As a nucleophile, phosphine can react with an allene to form a zwitterionic phosphoniopropenide intermediate. After stepwise cycloaddition and proton transfer, the phosphine catalyst can be regenerated by C?P bond cleavage. Alternatively, the zwitterionic phosphoniopropenide intermediate could also be protonated by a Brønsted acid to generate a phosphonium intermediate, which can be used to construct new C?C bonds by electrophilic addition. In this review, we have summarized details of mechanistic studies of phosphine‐catalyzed allene coupling reactions that follow these two reaction modes. In addition to detailing the reaction pathway, the regioselectivity and diastereoselectivity of the phosphine‐catalyzed allene coupling reaction are also discussed in this review. 相似文献
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Enantioselective Rhodium‐Catalyzed Dimerization of ω‐Allenyl Carboxylic Acids: Straightforward Synthesis of C2‐Symmetric Macrodiolides 下载免费PDF全文
Philip Steib Prof. Dr. Bernhard Breit 《Angewandte Chemie (International ed. in English)》2018,57(22):6572-6576
Herein, we report on the first enantioselective and atom‐efficient catalytic one‐step dimerization method to selectively transform ω‐allenyl carboxylic acids into C2‐symmetric 14‐ to 28‐membered bismacrolactones (macrodiolides). This convenient asymmetric access serves as an attractive route towards multiple naturally occuring homodimeric macrocyclic scaffolds and demonstrates excellent efficiency to construct the complex, symmetric core structures. By utilizing a rhodium catalyst with a modified chiral cyclopentylidene‐diop ligand, the desired diolides were obtained in good to high yields, high diastereoselectivity, and excellent enantioselectivity. 相似文献
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Heterobimetallic Catalysis: Platinum‐Gold‐Catalyzed Tandem Cyclization/C−X Coupling Reaction of (Hetero)Arylallenes with Nucleophiles 下载免费PDF全文
Dr. José Miguel Alonso Dr. María Paz Muñoz 《Angewandte Chemie (International ed. in English)》2018,57(17):4742-4746
Heterobimetallic catalysis offers new opportunities for reactivity and selectivity but still presents challenges, and only a few metal combinations have been explored so far. Reported here is a Pt‐Au heterobimetallic catalyst system for the synthesis of a family of multi‐heteroaromatic structures through tandem cyclization/C?X coupling reaction. Au‐catalyzed 6‐endo‐cyclization takes place as the first fast step. Pt‐Au clusters are proposed to be responsible for the increased reactivity in the second step, that is, the intermolecular nucleophilic addition which occurs through an outer‐sphere mechanism by hybrid homogeneous‐heterogeneous catalysis. 相似文献
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In this paper, it is reported that the efficient iodolactonization of 4,5-allenoic acid with I2 in cyclohexane in the presence or absence of K2CO3 afforded 5-(1'-iodo-1'(Z)-alkenyl)-4,5-dihydro-2(3H)-furanones highly stereoselectively. However, the reaction of axially optically active 4,5-allenoic acids (R)-(-)-5 a and (R)-(-)-5 b with I2 afforded the corresponding products with a serious loss of chirality. This problem was solved by conducting the iodolactonization with N-iodosuccinimide in CH2Cl2 in the presence of Cs2CO3; however, the Z/E selectivity is somewhat lower. The pure optically active Z products were prepared by subsequent kinetic resolution with Sonogashira coupling. The reaction of the substrates with a substituent at the 3-position of the starting 4,5-allenoic acids afforded the trans-4,5-disubstituted gamma-butyrolactones as the only products. The reaction of the 4,5-allenoic acids (S)-(+)-1 l, (R)-(-)-1 l, and (S)-(+)-1 m with a center chirality at the 3-position afforded the trans products with very high enantiopurity and up to 98:2 Z/E selectivity regardless of the axial chirality of the allene moiety. 相似文献
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Allenes (R2C=C=CR2) have been traditionally perceived to feature localized orthogonal π-bonds between the carbon centres. We have carried out quantum-mechanical studies of the organometallic allenes envisioned by the isolobal replacement of the terminal CH2 groups by the d8 Fe(CO)4 fragment. Our studies have identified two organometallic allenes viz. D2d symmetric [(μ-C)(Fe(CO)4)2] ( 2 ) and D3 symmetric [(μ-C)(Fe(CO)4)2] ( 3 ) with trigonal bipyramidal coordination at the Fe atoms. Compound 2 features the bridging carbon atom in an equatorial position with respect to the ligands on the TM centre, while 3 features the central carbon atom in an axial position. The bis-pseudoallylic anionic delocalisation proposed in the C2-C1-C3 spine of organic allene is retained in the organometallic allene 2 , and is transformed to a typical three-centre bis-allylic anionic delocalisation in the organometallic allene 3 . The topological analysis of electron density also indicates a bis-allylic anionic type delocalisation in the organometallic allenes. The quantitative bonding analysis using the EDA-NOCV method suggests a transition from classical electron-sharing bonding between the central carbon atom and the terminal groups in 1 to donor-acceptor bonding in 3 . Meanwhile, both electron-sharing and donor-acceptor bonding models are found to be probable heuristic bonding representations in the organometallic allene 2 . 相似文献