Azetidines are four-membered nitrogen-containing heterocycles that hold great promise in current medicinal chemistry due to their desirable pharmacokinetic effects. However, a lack of efficient ...synthetic methods to access functionalized azetidines has hampered their incorporation into pharmaceutical lead structures. As a 2+2 cycloaddition reaction between imines and alkenes, the aza Paternò-Büchi reaction arguably represents the most direct approach to functionalized azetidines. Hampered by competing reaction paths accessible upon photochemical excitation of the substrates, the current synthetic utility of these transformations is greatly restricted. We herein report the development of a visible light-enabled aza Paternò-Büchi reaction that surmounts existing limitations and represents a mild solution for the direct formation of functionalized azetidines from imine and alkene containing precursors.
The 2 + 2 photocycloaddition reaction between an imine and an alkene component, the aza Paternò-Büchi reaction, is one of the most efficient ways to synthesize functionalized azetidines. However, the ...application of the aza Paternò-Büchi reaction has been met with limited success due to the inherent challenges associated with this approach. This review covers the current scope and limitations of reported examples of aza Paternò-Büchi reactions in organic synthesis. An outlook is provided, which highlights recent improvements and the discovery of new reaction protocols that have overcome some long-standing challenges within this field of research.
This review discusses the current scope and limitations of the 2 + 2 photocycloaddition reaction between an imine and an alkene component, the aza Paternò-Büchi reaction, and highlights recent improvements within this area of research.
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IJS, KILJ, NUK, UL, UM, UPUK
A 14‐step synthesis of (+)‐cochlearol B is reported. This renoprotective meroterpenoid features a unique core structure containing a densely substituted cyclobutane ring with three stereocenters. Our ...strategy employed an organocatalytic Kabbe condensation in route to the key chromenyl triflate. A subsequent Catellani reaction incorporated the remaining carbon atoms featured in the skeleton of cochlearol B. An ensuing visible‐light‐mediated 2+2 photocycloaddition closed the cyclobutane and formed the central bicyclo3.2.0heptane core. Notably, careful design and tuning of the Catellani and photocycloaddition reactions proved crucial in overcoming undesired reactivity, including cyclopropanation reactions and 4+2 cycloadditions.
A 14‐step approach to (+)‐cochlearol B is reported. The strategy involves an organocatalytic Kabbe condensation, Catellani reaction, and visible‐light‐mediated 2+2 cycloaddition to rapidly access the core of this natural product. Careful design and tuning of the Catellani and photocycloaddition reactions proved crucial in overcoming undesired reactivity, including cyclopropanation reactions, and 4+2 cycloadditions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
An eight-step enantioselective synthesis of lingzhiol is described herein. The sense of an asymmetric Michael reaction is reversed by the choice of metal source, enabling facile access to both ...enantiomers. A spontaneous semipinacol ring contraction enables mild construction of the lingzhiol core, and radical-mediated benzylic oxidation proceeds in the presence of an unprotected secondary alcohol. This represents the shortest enantioselective synthesis of lingzhiol to date and the only enantiodivergent approach to both enantiomers of this meroterpenoid natural product.
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IJS, KILJ, NUK, PNG, UL, UM
Enantiodivergence is an important concept in asymmetric catalysis that enables access to both enantiomers of a product relying on the same chiral source as reagent. This strategy is particularly ...appealing as an alternate approach when only one enantiomer of the required chiral ligand is readily accessible but both enantiomers of the product are desired. Despite the potential significance, general catalytic methods to effectively reverse enantioselectivity by changing an achiral reaction parameter remain underdeveloped. Herein we report our studies focused on elucidating the origin of metal-controlled enantioselectivity reversal in Lewis acid-catalysed Michael additions. Rigorous experimental and computational investigations reveal that specific Lewis and Brønsted acid interactions between the substrate and ligand change depending on the ionic radius of the metal catalyst, and are key factors responsible for the observed enantiodivergence. This holds potential to further our understanding of and facilitate the design of future enantiodivergent transformations.
Enantiodivergence is an important concept in asymmetric catalysis that enables access to both enantiomers of a product relying on the same chiral source as reagent.
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Marine traffic is increasing globally yet collisions with endangered megafauna such as whales, sea turtles, and planktivorous sharks go largely undetected or unreported. Collisions leading to ...mortality can have population-level consequences for endangered species. Hence, identifying simultaneous space use of megafauna and shipping throughout ranges may reveal as-yet-unknown spatial targets requiring conservation. However, global studies tracking megafauna and shipping occurrences are lacking. Here we combine satellite-tracked movements of the whale shark, Rhincodon typus, and vessel activity to show that 92% of sharks’ horizontal space use and nearly 50% of vertical space use overlap with persistent large vessel (>300 gross tons) traffic. Collision-risk estimates correlated with reported whale shark mortality from ship strikes, indicating higher mortality in areas with greatest overlap. Hotspots of potential collision risk were evident in all major oceans, predominantly from overlap with cargo and tanker vessels, and were concentrated in gulf regions, where dense traffic co-occurred with seasonal shark movements. Nearly a third of whale shark hotspots overlapped with the highest collision-risk areas, with the last known locations of tracked sharks coinciding with busier shipping routes more often than expected. Depth-recording tags provided evidence for sinking, likely dead, whale sharks, suggesting substantial “cryptic” lethal ship strikes are possible, which could explain why whale shark population declines continue despite international protection and low fishing-induced mortality. Mitigation measures to reduce ship-strike risk should be considered to conserve this species and other ocean giants that are likely experiencing similar impacts from growing global vessel traffic.
Herein we describe the application of Lewis-acid-catalyzed carbonyl–olefin metathesis toward the synthesis of substituted tetrahydropyridines from commercially available amino acids as chiral pool ...reagents. This strategy relies on FeCl3 as an inexpensive and environmentally benign catalyst and enables access to a variety of substituted tetrahydropyridines under mild reaction conditions. The reaction proceeds with complete stereoretention and is viable for a variety of natural and unnatural amino acids to provide the corresponding tetrahydropyridines in up to 99% yield.
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IJS, KILJ, NUK, PNG, UL, UM
Herein we describe the application of Lewis-acid-catalyzed carbonyl-olefin metathesis toward the synthesis of substituted tetrahydropyridines from commercially available amino acids as chiral pool ...reagents. This strategy relies on FeCl
as an inexpensive and environmentally benign catalyst and enables access to a variety of substituted tetrahydropyridines under mild reaction conditions. The reaction proceeds with complete stereoretention and is viable for a variety of natural and unnatural amino acids to provide the corresponding tetrahydropyridines in up to 99% yield.
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IJS, KILJ, NUK, PNG, UL, UM
A 14‐step synthesis of (+)‐cochlearol B is reported. This renoprotective meroterpenoid features a unique core structure containing a densely substituted cyclobutane ring with three stereocenters. Our ...strategy employed an organocatalytic Kabbe condensation in route to the key chromenyl triflate. A subsequent Catellani reaction incorporated the remaining carbon atoms featured in the skeleton of cochlearol B. An ensuing visible‐light‐mediated 2+2 photocycloaddition closed the cyclobutane and formed the central bicyclo3.2.0heptane core. Notably, careful design and tuning of the Catellani and photocycloaddition reactions proved crucial in overcoming undesired reactivity, including cyclopropanation reactions and 4+2 cycloadditions.
A 14‐step approach to (+)‐cochlearol B is reported. The strategy involves an organocatalytic Kabbe condensation, Catellani reaction, and visible‐light‐mediated 2+2 cycloaddition to rapidly access the core of this natural product. Careful design and tuning of the Catellani and photocycloaddition reactions proved crucial in overcoming undesired reactivity, including cyclopropanation reactions, and 4+2 cycloadditions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Reaction of Cu(II) halides with isoquinoline in neutral/acidic media produces a family of complexes whose magnetostructural correlations are reported.
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The compounds (iQuin)2CuX2 ...(X = Br (1), Cl (2)), (iQuinH)2CuBr4·H2O (3) and two polymorphs of (iQuinH)2CuCl4 (4, 5) (iQuin = isoquinoline) have been prepared and studied via X-ray crystallography and variable temperature magnetic susceptibility measurements. Compound 1 crystallizes in the monoclinic space group P21/n while 3, 4 and 5 all crystallize in the triclinic space group P1¯). Magnetic susceptibility measurements for 1 are best fit by an antiferromagnetic alternating chain model (J/kB = −56.6(2) K, J′/kB = 5.1(8) K) although the crystal structure suggests a uniform chain. Compound 2 is well described as an isolated uniform antiferromagnetic chain (J/kB = −25.6(1) K), while 3 agrees well with the antiferromagnetic rectangular model (J/kB = −5. 03(2) K, J′/kB = −1.0(1) K). The two polymorphs, 4 and 5, exhibit distinctly different behavior as 4 is well described by the 2D-square antiferromagnetic layer model (J/kB = −4.24(2) K), but 5 crystallizes as well isolated magnetic dimers (J/kB = −15.8(1) K). Magnetic superexchange is proposed to occur via either the bihalide or two-halide pathways. Finally, compound 6, isoquinolinium tribromide, was isolated as a biproduct of the synthesis of 3 and was characterized via X-ray diffraction. The formation of the tribromide ion in situ provides support for the mechanism of electrophilic aromatic bromination reactions which have been previously observed in syntheses similar to that of 3.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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