Divergent asymmetric synthesis of azaarene-functionalized cyclic alcohols through stereocontrolled Beckwith-Enholm cyclizations
TL;DR: The first enantioselective Beckwith-Enholm cyclization reaction was reported in this paper, where azaarene-based olefins were used as a new reaction system.
Abstract: The first enantioselective Beckwith-Enholm cyclization reaction is reported herein. Under cooperative photoredox and chiral hydrogen-bonding catalysis mediated by visible light, cyclization of carbonyls with azaarene-based olefins as a new reaction system offers a general and divergent synthetic pathway to furnish a variety of highly valuable enantioenriched azaarene-functionalized carbocyclic and heterocyclic alcohols, which bear adjacent 1,2- or nonadjacent 1,3-stereocentres on distinct cyclic frameworks, in high yields and enantio- and diastereoselectivities. The good compatibility of various azaarenes and carbonyls as well as the diversity of cyclic structures of the products underscores the generality of the catalysis platform. In addition to the ability to precisely introduce deuterium into molecules in an enantioselective manner, the considerable synthetic value of this method includes the excellent antioxidant stress potential of the products. In particular, molecule 29 was determined to be a promising lead compound for antioxidant stress drug design.
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TL;DR: Cooperative hydrogen atom transfer and chiral hydrogen-bonding catalysis as a new platform for the asymmetric synthesis of azaarene derivatives is reported in this article , which enables a highly practical and concise synthesis of the enantiomerically pure medicinal molecule pheniramine (Avil).
13 citations
12 citations
TL;DR: In this paper , the authors developed time-atom economic regio- and chemoselective sulfonyl radical triggered 5-exo-dig cyclization of unactivated 1,6-enynes with sulfonyls halides under metal, additive-free reaction conditions to achieve highly substituted five-membered heterocyclic compounds.
Abstract: We developed time-atom economic regio- and chemoselective sulfonyl radical triggered 5-exo-dig cyclization of unactivated 1,6-enynes with sulfonyl halides under metal, additive-free reaction conditions to achieve highly substituted five-membered heterocyclic compounds. This transformation creates three new bonds, such as C-SO2 , C-C, and active C-I/Br bonds. Importantly, one-pot protocols produce desired products directly from sodium sulfinates and have an additional advantage such as minimising chemical waste, saving time, and simplifying practical aspects compared to existing protocols.
6 citations
TL;DR: In this article , an array of chiral molecules bearing azaaryl groups is synthesized in moderate-to-excellent yields with high dr, and excellent enantioselectivity by a copper(I)-catalyzed asymmetric conjugate addition of 1,4-dienes to (E)-β-substituted alkenyl azaarenes.
Abstract: Chiral azaarene compounds are extremely important due to their prevalence in pharmaceutical ingredients. Herein, an array of chiral molecules bearing azaaryl groups is synthesized in moderate-to-excellent yields with moderate-to-excellent Z/E ratios, high dr, and excellent enantioselectivity by a copper(I)-catalyzed asymmetric conjugate addition of 1,4-dienes to (E)-β-substituted alkenyl azaarenes. The reaction is carried out under mild proton-transfer conditions, which enjoys very high atom economy. Moreover, the reaction features a broad substrate scope on (E)-α,β-unsaturated azaarenes as various azaarenes are well tolerated, such as benzothiazole, thiazole, N-methyl-benzimidazole, benzoxazole, quinoline, isoquinoline, pyrimidine, pyrazine, and triazine. Interestingly, the reaction with (Z)-α,β-unsaturated azaarenes affords the same products in excellent results but with a reversed absolute configuration. DFT calculations indicate that the C-C bond-forming nucleophilic addition is a Z-/E- and enantio-selectivities-determining step and provides a rationale for the origin of selectivities. At last, the synthetic utilities of the product are showcased by several transformations, including olefin metathesis, [4 + 2] cyclization, [2 + 1] cyclization, and cleavage of the benzothiazole ring.
5 citations
TL;DR: In this article , an enantioselective reductive cross coupling of electron-deficient olefins was reported using cooperative photoredox and chiral Brønsted acid-catalyzed reaction with a Hantzsch ester as the terminal reductant.
4 citations
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TL;DR: An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.
Abstract: In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.
3,550 citations
TL;DR: In this Perspective, some contemporary themes exploring the role of isosteres in drug design are sampled, with an emphasis placed on tactical applications designed to solve the kinds of problems that impinge on compound optimization and the long-term success of drug candidates.
Abstract: The concept of isosterism between relatively simple chemical entities was originally contemplated by James Moir in 1909, a notion further refined by H. G. Grimm’s hydride displacement law and captured more effectively in the ideas advanced by Irving Langmuir based on experimental observations. Langmuir coined the term “isostere” and, 18 years in advance of its actual isolation and characterization, predicted that the physical properties of the then unknown ketene would resemble those of diazomethane. The emergence of bioisosteres as structurally distinct compounds recognized similarly by biological systems has its origins in a series of studies published byHans Erlenmeyer in the 1930s, who extended earlier work conducted by Karl Landsteiner. Erlenmeyer showed that antibodies were unable to discriminate between phenyl and thienyl rings or O, NH, and CH2 in the context of artificial antigens derived by reacting diazonium ions with proteins, a process that derivatized the ortho position of tyrosine, as summarized in Figure 1 The term “bioisostere” was introduced by Harris Friedman in 1950 who defined it as compounds eliciting a similar biological effect while recognizing that compounds may be isosteric but not necessarily bioisosteric. This notion anticipates that the application of bioisosterism will depend on context, relying much less on physicochemical properties as the underlying principle for biochemical mimicry. Bioisosteres are typically less than exact structural mimetics and are often more alike in biological rather than physical properties. Thus, an effective bioisostere for one biochemical application may not translate to another setting, necessitating the careful selection and tailoring of an isostere for a specific circumstance. Consequently, the design of bioisosteres frequently introduces structural changes that can be beneficial or deleterious depending on the context, with size, shape, electronic distribution, polarizability, dipole, polarity, lipophilicity, and pKa potentially playing key contributing roles in molecular recognition and mimicry. In the contemporary practice of medicinal chemistry, the development and application of bioisosteres have been adopted as a fundamental tactical approach useful to address a number of aspects associated with the design and development of drug candidates. The established utility of bioisosteres is broad in nature, extending to improving potency, enhancing selectivity, altering physical properties, reducing or redirecting metabolism, eliminating or modifying toxicophores, and acquiring novel intellectual property. In this Perspective, some contemporary themes exploring the role of isosteres in drug design are sampled, with an emphasis placed on tactical applications designed to solve the kinds of problems that impinge on compound optimization and the long-term success of drug candidates. Interesting concepts that may have been poorly effective in the context examined are captured, since the ideas may have merit in alternative circumstances. A comprehensive cataloging of bioisosteres is beyond the scope of what will be provided, although a synopsis of relevant isosteres of a particular functionality is summarized in a succinct fashion in several sections. Isosterism has also found productive application in the design and optimization of organocatalysts, and there are several examples in which functional mimicry established initially in a medicinal chemistry setting has been adopted by this community.
2,049 citations
TL;DR: This Perspective highlights the unique ability of photoredox catalysis to expedite the development of completely new reaction mechanisms, with particular emphasis placed on multicatalytic strategies that enable the construction of challenging carbon-carbon and carbon-heteroatom bonds.
Abstract: In recent years, photoredox catalysis has come to the forefront in organic chemistry as a powerful strategy for the activation of small molecules. In a general sense, these approaches rely on the ability of metal complexes and organic dyes to convert visible light into chemical energy by engaging in single-electron transfer with organic substrates, thereby generating reactive intermediates. In this Perspective, we highlight the unique ability of photoredox catalysis to expedite the development of completely new reaction mechanisms, with particular emphasis placed on multicatalytic strategies that enable the construction of challenging carbon–carbon and carbon–heteroatom bonds.
1,808 citations
TL;DR: Analysis of keap1-knockout mice provides solid evidence that Keap1 acts as a negative regulator of Nrf2 and as a sensor of xenobiotic and oxidative stresses.
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