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Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters 下载免费PDF全文
Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
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Christoph M. Hendrich Sebastian Senn Lea Haas Marvin T. Hoffmann Dr. Ute Zschieschang Luca C. Greiner Dr. Frank Rominger Dr. Matthias Rudolph Dr. Hagen Klauk Prof. Dr. Andreas Dreuw Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(59):14778-14784
Herein, we describe a gold-catalyzed cascade cyclization of Boc-protected benzylamines bearing two tethered alkyne moieties in a domino reaction initiated by a 6-endo-dig cyclization. The reaction was screened intensively, and the scope was explored, resulting in nine new Boc-protected dihydrobenzo[c]phenanthridines with yields of up to 98 %; even a π-extension and two bidirectional approaches were successful. Furthermore, thermal cleavage of the Boc group and subsequent oxidation gave substituted benzo[c]phenanthridines in up to quantitative yields. Two bidirectional approaches under the optimized conditions were successful, and the resulting π-extended molecules were tested as organic semiconductors in organic thin-film transistors. 相似文献
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Mechanistic Insights into the Post‐Cyclization Isomerization in Gold‐Catalyzed 7‐exo‐dig‐Hydroarylations 下载免费PDF全文
M. Sc. Daniel Pflästerer Sören Schumacher Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(32):11585-11589
The subsequent double‐bond isomerization in the synthesis of dibenzocycloheptenes and their heteroaromatic analogues was investigated. In the case of biphenyls, a basic additive completely prevented an isomerization to the thermodynamic product. With electron‐rich intramolecular heteroaromatic nucleophiles, the isomerization was still observed, but the kinetic product can be obtained by careful control of the reaction times in most cases. Mechanistic studies demonstrated that a slow isomerization is also possible with the gold catalyst at elevated temperatures, but much faster isomerization rates were observed with acidic additives. An observed initiation period for the gold‐catalyzed isomerization indicates that not the homogenous catalyst, but a decomposition product of it may be the catalytically active species. 相似文献
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M. Sc. Steffen Mader Dr. Lise Molinari Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):3910-3913
Various haloalkynes are converted in the presence of a dual activation gold catalyst. Via a dual activation process a completely atom economic head‐to‐tail coupling delivers gem‐dihalogenated conjugated enynes as valuable building blocks for organic synthesis. 相似文献
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Mohammad Vatankhah‐Varnoosfaderani Amin GhavamiNejad Saud Hashmi Florian J. Stadler 《Macromolecular rapid communications》2015,36(5):447-452
Copolymers of N‐isopropylacrylamide (NIPAM) and dopamine methacrylate can establish a reversible, self‐healing 3D network in aprotic solvents based on hydrogen bonding. The reactivity and hydrogen bonding formation of catechol groups in copolymer chains are studied by UV–vis and 1H NMR spectroscopy, while reversibility from sol to gel and inverse as well as self‐healing properties are tested rheologically. The produced reversible organogel can self‐encapsulate physically interacting or chemically bonded solutes such as drugs due to thermosensitivity of the used copolymer. This system offers dual‐targeted and controlled drug delivery and release—by slowing down release kinetics by supramolecular bonding of the drug and by reducing diffusion rates due to modulus increase.
9.
Alejandro Cervantes-Reyes Dr. Frank Rominger Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(24):5530-5540
The synthesis and full characterization of new air-stable AgI and CuI complexes bearing structurally bulky expanded-ring N-heterocyclic carbene (erNHC) ligands is presented. The condensation of protonated NHC salts with Ag2O afforded a collection of AgI complexes, and their first use as ligand transfer reagents led to novel isostructural CuI or AuI complexes. In situ deprotonation of the NHC salts in the presence of a copper(I) source, provides a library of new CuI complexes. The solid-state structures feature large N-CNHC-N angles (118–128°) and almost identical angles between the aryl groups on the nitrogen atoms and the plane of the N-C-N unit of the carbene (i.e. torsion angles close to 0°). Among the steric parameters, the percent buried volume (%Vbur) values span easily in the 50–57 % range, and that one of (9-Dipp)CuBr complex (%Vbur=57.5) overcomes to other known erNHC–metal complexes reported to date. Preliminary catalytic experiments in the copper-catalyzed coupling between N-tosylhydrazone and phenylacetylene, afforded 76–93 % product at the 0.5–2.5 mol % catalyst loading, proving the stability of CuI erNHC complexes at elevated temperatures (100 °C). 相似文献
10.
Dehydrogenative Meyer–Schuster‐Like Rearrangement: A Gold‐Catalyzed Reaction Generating an Alkyne 下载免费PDF全文
M. Sc. Yang Yu M. Sc. Weibo Yang M. Sc. Daniel Pflästerer Prof. Dr. A. Stephen K. Hashmi 《Angewandte Chemie (International ed. in English)》2014,53(4):1144-1147
Easily accessible propargylic esters are converted to the inverted alkynyl ketones in an oxidative gold‐catalyzed reaction. Gagosz’s catalyst in combination with PhI(OAc)2 is the best system for this conversion and 18 examples with yields up to 80 % are reported. The results indicate that the triple bond in the product is formed by elimination from a vinylgold intermediate. In a formal sense the new conversion overall is a dehydrogenative Meyer–Schuster rearrangement. 相似文献