938-94-3Relevant articles and documents
Number and Structure of Solvolysis Intermediates. IV. The Phenolysis of 1-(p-Tolyl)ethyl p-Nitrobenzoate: The Mechanism via a Single Stable Ion-Pair Intermediate with High Selectivity for Nucleophiles
Kinoshita, Tomomi,Shibayama, Koichi,Takemoto, Masaki,Takeuchi, Ken'ichi
, p. 816 - 823 (1994)
Optically active 1-(p-tolyl)ethyl p-nitrobenzoate (ROPNB) has been subjected to solvolysis in phenol where the solvolysis was previously found to proceed via a single stable ion-pair intermediate (Int-1) with high selectivity for nucleophiles, i.e., to exhibit the kinetic features expressed by the "B" pattern for the kp-kt profile.On the basis of the absolute configurations and the maximum rotations for the substrate and all of the products which have been chemically established, the stereochemical courses have been disclosed to be partial retention for POPh formation ("retentive phenolysis") and partial inversion for o- and p-RC6H4OH formation with predominant racemization in the solvolysis.These stereochemical outcomes indicate that the key intermediate (Int-1) which provides all of the products should have the structure of a carbocation ion pair shielded at the rear side by a phenol molecule (the rear-side shielded ion-pair intermediate) similarly to the key intermediates which are known for some other phenolysis systems.Consequently, the rear-side shielded ion-pair intermediate plays a key role regarding product formation in all retentive phenolysis systems.
Catalytic α-Deracemization of Ketones Enabled by Photoredox Deprotonation and Enantioselective Protonation
Chen, Shuming,Gao, Anthony Z.,Ivlev, Sergei I.,Meggers, Eric,Nie, Xin,Ye, Chen-Xi,Zhang, Chenhao
supporting information, p. 13393 - 13400 (2021/09/03)
This study reports the catalytic deracemization of ketones bearing stereocenters in the α-position in a single reaction via deprotonation, followed by enantioselective protonation. The principle of microscopic reversibility, which has previously rendered this strategy elusive, is overcome by a photoredox deprotonation through single electron transfer and subsequent hydrogen atom transfer (HAT). Specifically, the irradiation of racemic pyridylketones in the presence of a single photocatalyst and a tertiary amine provides nonracemic carbonyl compounds with up to 97% enantiomeric excess. The photocatalyst harvests the visible light, induces the redox process, and is responsible for the asymmetric induction, while the amine serves as a single electron donor, HAT reagent, and proton source. This conceptually simple light-driven strategy of coupling a photoredox deprotonation with a stereocontrolled protonation, in conjunction with an enrichment process, serves as a blueprint for other deracemizations of ubiquitous carbonyl compounds.
1,3,2-Diazaphospholenes Catalyze the Conjugate Reduction of Substituted Acrylic Acids
Reed, John H.,Cramer, Nicolai
, p. 4262 - 4266 (2020/07/13)
The potent nucleophilicity and remarkably low basicity of 1,3,2-diazaphospholenes (DAPs) is exploited in a catalytic, metal-free 1,4-reduction of free α,β-unsaturated carboxylic acids. Notably, the reduction occurs without a prior deprotonation of the carboxylic acid moiety and hence does not consume an additional hydride equivalent. This highlights the excellent nucleophilic character and low basicity of DAP-hydrides. Functional groups such as Cbz group or alkyl halides which can be problematic with classical transition-metal catalysts are well tolerated in the DAP-catalyzed process. Moreover, the transformation is characterized by a low catalyst loading, mild reaction conditions at ambient temperature as well as fast reaction times and high yields. The proof-of-principle for a catalytic enantioselective version is described.
