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71.
On direct photolysis of 2,2-dialkyl-5-diazo-4,6-dioxo-1,3-dioxanes in the presence of pyridine, methanol or dimethyl sulfide as carbene traps, the yield of ‘carbene’ products does not exceed 27-28%. At the same time photochemical transformations of the related 3,3-diacyldiazirines and dioxosulfonium ylides of this series, evidently, occur without generation of carbene intermediates. 相似文献
72.
The reaction of aryldiazoacetates with enamines catalyzed by copper and rhodium complexes provided γ-keto esters in good yields. A full investigation of the effects of solvents, catalysts, enamines and aryldiazoacetates on the reaction was carried out. Careful analysis of the crude reaction mixture revealed a substituted enamine as the primary product, which was hydrolyzed over silica gel to give a γ-keto ester as the final product. A reaction mechanism involving nucleophilic addition of an enamine to a metal carbene and subsequent hydrogen transfer was proposed. Chiral dirhodium and copper catalysts were examined and found to provide γ-keto esters with no enantioselectivity. The result could be rationalized based on the proposed reaction mechanism. Attempts to trap the enamine intermediate with several electrophilic reagents were not successful. 相似文献
73.
A 3-monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide, was prepared for the first time, by the reaction of (9-triptycyl)diazomethane and S8O. The dithiirane 1-oxide was obtained as cis- and trans-isomers, and the structure of the trans-isomer was verified by X-ray crystallography. The cis-isomer isomerized gradually to the trans-isomer in solution. The divalent sulfur atom of the cis- and trans-dithiirane 1-oxides were removed on treatment with triphenylphosphine to give the corresponding Z- and E-sulfines, respectively. The reaction of the trans-dithiirane 1-oxide with (Ph3P)2Pt(C2H4) provided the (sulfenato-thiolato)PtII complex, and that with Lawesson's reagent yielded the 1,3,4,2-trithiaphospholane and 1,2,4,5,3-tetrathiaphosphorinane derivatives. 相似文献
74.
Pentacarbonyl(η2-cis-cyclooctene)chromium(0) (1) catalyzes efficiently reactions of diazo compounds with electron-rich furans. The reaction of 2-methoxyfuran (2) with alkyl α-diazoarylacetate (3a-g) furnishes the (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g) in excellent yields. These reactions are highly regioselective. The cyclopropanation intermediates formed from 1 and diazo compounds 3a-g always arise from a carbene addition to the less substituted CC bond of 2. The resulting cyclopropanation product undergoes a ring opening reaction to form the corresponding (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g). The pentacarbonylchromium(0)-catalyzed reactions of 2-alkylfuran (5a-b) with ethyl α-diazophenylacetate (3a) and 9-diazo-9H-fluorene (3h) produce the 1(E),3(E)-butadienes (6a-d) in very good yields. 相似文献
75.
Dr. Shengjie Jiang Yanping Cai Thayalan Rajeshkumar Iker del Rosal Prof. Dr. Laurent Maron Prof. Dr. Xin Xu 《Angewandte Chemie (International ed. in English)》2023,62(34):e202307244
This work reports the synthesis, characterization, and reactivity of the first example of a well-defined zinc α-diazoalkyl complex. Treatment of zinc(I)-zinc(I) bonded compound L 2Zn2 [ L =CH3C(2,6-iPr2C6H3N)CHC(CH3)(NCH2CH2PPh2)] or zinc(II) hydride L ZnH with trimethylsilyldiazomethane affords zinc diazoalkyl complex L ZnC(N2)SiMe3. This complex liberates N2 in the presence of a nickel catalyst to form an α-zincated phosphorus ylide by reacting with the pendant phosphine. It selectively undergoes formal [3+2] cycloaddition with CO2 or CO to form the corresponding product with a five-membered heterocyclic core. Notably, the use of CO in such a [3+2] cycloaddition reaction is unprecedented, reflecting a novel CO reaction mode. 相似文献
76.
Dr. Kai Wu Xuyang Zhang Dr. Liang-Liang Wu Dr. Jie-Sheng Huang Prof. Dr. Chi-Ming Che 《Angewandte Chemie (International ed. in English)》2023,62(9):e202215891
Trifluoromethyl-bearing 5-membered rings are prevalent in bioactive molecules, but modular approaches to these compounds by functionalization of robust C(sp3)−H bonds in a direct and selective manner are extremely challenging. Herein we report the rhodium-catalyzed α-CF3-α-alkyl carbene insertion into C(sp3)−H bonds of a broad range of substrates to access 7 types of CF3-bearing saturated 5-membered carbo- and heterocycles. The reaction is particularly effective for benzylic C−H insertion exerting good site-, diastereo- and enantiocontrol, and applicable to the synthesis of chiral CF3 analogues of bioactive molecules. Ruthenium α-CF3-α-alkyl carbene complexes underwent stoichiometric reactions to give C−H insertion products, lending evidence for the involvement of metal α-CF3-α-alkyl carbene species in the catalytic cycle. DFT calculations revealed that the π⋅⋅⋅π attraction and intra-carbene C−H⋅⋅⋅F hydrogen bond elucidate the origin of selectivity of the benzylic C−H insertion reactions. 相似文献
77.
Albert Padwa Majid J. Chughtai Jutatip Boonsombat Paitoon Rashatasakhon 《Tetrahedron》2008,64(21):4758-4767
Using a rhodium(II)-catalyzed cyclization/cycloaddition sequence as the key reaction step, the icetexane core of komaroviquinone was constructed by an intramolecular dipolar-cycloaddition of a carbonyl ylide dipole across a tethered π-bond. The ylide was arrived at by cyclization of a rhodium carbenoid intermediate onto a proximal ester group. Efforts toward the preparation of the required precursor for elaboration to the natural product are discussed. 相似文献
78.
A wide variety of new macrocyclic diazocarbonyl compounds with various spacers was synthesized. Macrocyclic rhodium(II) carbenoid insertion with various substituted indoles was performed to afford regioselectively, indol-3-yl macrocyclic di- or tetralactones (C3-alkylation). Double carbenoid insertion was also performed to afford indolyl cryptand molecules. 相似文献
79.
Diazo compounds are frequently used as precursors of metal carbenoids and act as soft nucleophiles even without the use of metal catalysts. The resulting diazonium species may also be trapped by various nucleophiles. The introduction of an iodine functionality applicable for the coupling reaction into an alkenyl diazo compound, however, has not been reported. We developed iodoalkoxylation reactions of alkenyl diazoacetates using an electrophilic iodinating reagent and oxygen nucleophile. This catalyst-free multicomponent reaction proceeded regioselectively, furnishing trisubstituted vinyl iodides in 31%–71% yield. The synthesized iodoalkenes were converted into the corresponding olefins with various functionalities in good yield via Suzuki-Miyaura coupling reactions with arylboronic acids under palladium catalysis to demonstrate the synthetic utility of the developed reaction sequence. 相似文献
80.
The transition-metal-catalyzed reaction of diazo compounds with arenes or heteroarenes is an efficient and straightforward approach to functionalize aromatic compounds. This digest summarizes recent progresses on transition-metal-catalyzed asymmetric reactions of diazo compounds with electron-rich (hetero-) arenes, including C–H functionalization, cascade reaction, cyclopropanation, cycloaddition, Buchner reaction and intramolecular dearomatization. 相似文献