- Metal-Free Direct C?H Cyanation of Alkenes
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A metal-free and direct alkene C?H cyanation is described. Directing groups are not required and the mechanism involves electrophilic activation of the alkene by a cyano iodine(III) species generated in situ from a [bis(trifluoroacetoxy)iodo]arene and tri
- Wang, Xi,Studer, Armido
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supporting information
p. 11792 - 11796
(2018/09/10)
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- Photocatalytic E → Z isomerization of polarized alkenes inspired by the visual cycle: Mechanistic dichotomy and origin of selectivity
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Iteratively executed with exquisite spatial and temporal control, the selective isomerization of polarized alkenes underpins a plethora of complex biological processes ranging from natural product biosynthesis through to the mammalian visual cycle. However, nature's proficiency conceals the inherent difficulties in replicating this contrathermodynamic transformation in the laboratory. Recently, we disclosed the first highly Z-selective isomerization of polarized alkenes, employing the cinnamoyl chromophore as a retinal surrogate under UV-irradiation (402 nm) with (-)-riboflavin (Vitamin B2) as an inexpensive, organic photocatalyst (J. Am. Chem. Soc. 2015, 137, 11254-11257). This study was inspired by the propensity of crystalline (-)-riboflavin in the eyes of vertebrates to invert the intrinsic directionality of retinal isomerization. Herein, we extend this methodology to include a bioinspired, catalytic E → Z isomerization of α,β-unsaturated nitriles, thereby mimicking the intermediate Opsin-derived, protonated Schiff base in the visual cycle with simple polarized alkenes. Replacement of the iminium motif by a cyano group is well tolerated and gives an additional degree of versatility for postisomerization functionalization. Broad substrate scope is demonstrated (up to 99:1 Z:E) together with evidence of mechanistic dichotomy via both singlet and triplet energy transfer mechanisms. Kinetic studies, temperature dependent photostationary state correlations and investigation of substituent-based electronic perturbation of the alkene identified polarization combined with increased Z-isomer activation barriers as the selectivity governing factors in catalysis. This investigation demonstrates the importance of internal structural preorganization on photostationary composition and explicates the augmented Z-selectivity upon hydrogen-alkyl exchange at the β-position of the alkene.
- Metternich, Jan B.,Artiukhin, Denis G.,Holland, Mareike C.,Von Bremen-Kuhne, Maximilian,Neugebauer, Johannes,Gilmour, Ryan
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p. 9955 - 9977
(2018/05/31)
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- Highly efficient Rh-catalyzed asymmetric hydrogenation of α,β-unsaturated nitriles
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A highly efficient enantioselective hydrogenation of α,β-unsaturated nitriles catalyzed by Rh-(R,R)-f-spiroPhos complex has been developed. With Rh-(R,R)-f-spiroPhos catalyst and under mild conditions, a wide range of α,β-unsaturated nitriles including the (E)- and (Z)-isomers of 3-alkyl-3-aryl, 3,3-diaryl, and 3,3-dialkyl α,β-unsaturated nitriles were hydrogenated to the corresponding chiral nitriles with excellent enantioselectivities (up to 99.9% ee) and high turnover numbers (TON up to 10,000).
- Yan, Qiaozhi,Kong, Duanyang,Li, Meina,Hou, Guohua,Zi, Guofu
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supporting information
p. 10177 - 10181
(2015/09/01)
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- Asymmetric hydrogenation of α,β-unsaturated nitriles with base-activated iridium N,P ligand complexes
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Although many chiral catalysts are known that allow highly enantioselective hydrogenation of a wide range of olefins, no suitable catalysts for the asymmetric hydrogenation of α,β-unsaturated nitriles have been reported so far. We have found that Ir N,P ligand complexes, which under normal conditions do not show any reactivity towards α,β-unsaturated nitriles, become highly active catalysts upon addition of N,N- diisopropylethylamine. The base-activated catalysts enable conjugate reduction of α,β-unsaturated nitriles with H2 at low catalyst loadings, affording the corresponding saturated nitriles with high conversion and excellent enantioselectivity. In contrast, alkenes lacking a conjugated cyano group do not react under these conditions, making it possible to selectively reduce the conjugated C=C bond of an α,β-unsaturated nitrile, while leaving other types of C=C bonds in the molecule intact.
- Mueller, Marc-Andre,Pfaltz, Andreas
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supporting information
p. 8668 - 8671
(2014/08/18)
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- Bronsted acid mediated nitrogenation of propargylic alcohols: An efficient approach to alkenyl nitriles
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A novel and efficient approach to alkenyl nitriles from readily available propargylic alcohols has been developed. This nitrogenation reaction is transition-metal-free and could be conducted under air at ambient temperature, which makes this protocol promising and practical. Moreover, NH4Br is disclosed as an efficient additive to promote the stereoselectivity of this reaction. the Partner Organisations 2014.
- Huang, Xiaoqiang,Jiao, Ning
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supporting information
p. 4324 - 4328
(2014/06/23)
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- TWO CONVENIENT SYNTHESES OF 2-ARYL-1-CYANO-1-PROPENES FROM QUATERNARY AMMONIUM SALTS
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Two readily available and different quaternary ammonium salts have been prepared by the alkylation of vinamidinium salt reduction products.These salts have been successfully converted to 2-aryl-1-cyano-1-propenes and this methodology represents a clean an
- Gupton, John T.,Zembower, David,Miller, John
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p. 1891 - 1903
(2007/10/02)
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