Chiral Primary Amine Catalyzed Enantioselective Protonation via an Enamine Intermediate

Two examples of a rare class of di-radical azo-anion complexes of 2-(arylazo) pyridine with Ir(III) carrier are introduced. Their electronic structures have been elucidated using a host of physical methods that include X-ray crystallography, cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory. Room temperature magnetic moments of these are consistent with two nearly non-interacting azo-anion radicals. These displayed rich electrochemical properties consisting of six numbers of reversible and successive one electron CV-waves. Redox processes occur entirely at the coordinated ligands without affecting metal redox state. Apart from reporting their chemical characterization, I-V characteristics of these complexes in film state are investigated using sandwich-type devices comprising of a thin film of 100-125 nm thickness placed between two gold-plated ITO electrodes. These showed memory switching properties covering a useful voltage range with a reasonable ON/OFF ratio and also are suitable for RAM/ROM applications. I-V characteristics of two similar complexes of Rh and Cr with identical ligand environment and electronic structure are also referred for developing an insight into the memory switching ability of Ir- and Rh- complexes on the basis of comparative analysis of responses of the respective systems. In a nutshell, thorough analysis of voltage driven redox dynamics and corresponding solid and solution state current responses of all the systems are attempted and there from an unexplored class of switching devices are systematically introduced.

Section: Asymmetric Protonation Of Catalytically Generated Carbanionsmentioning

confidence: 99%

Redox Non‐Innocence of Coordinated 2‐(Arylazo) Pyridines in Iridium Complexes: Characterization of Redox Series and an Insight into Voltage‐Induced Current Characteristics

Goswami

Sengupta

Paul

et al. 2014

“…The chiral induction does not take place during the CC bond formation, but in the subsequent protonation step. Good to very good yields and excellent ee values are observed 299…”

Section: Miscellaneous Reactionsmentioning

confidence: 80%

Recent Advances in Organocatalytic Methods for Asymmetric CC Bond Formation

Scheffler

Mahrwald

2013

191

Beyond a doubt organocatalysis belongs to the most exciting and innovative chapters of organic chemistry today. Organocatalysis has emerged not only as a complement to metal-catalyzed reactions and to biocatalysis over the last decade, but also provides new asymmetric organocatalyzed reactions that cannot be accomplished by metal- or biocatalyzed reactions so far. A large number of organocatalytic processes are already well established in organic synthesis. Nevertheless, the number of publications in this field is still on the increase; new important results are produced constantly. This review gives a detailed overview of the latest developments and main streams in organocatalyzed asymmetric CC bond formation processes of the last three years. It is intended to outline the most important current findings focused on especially new synthetic methodologies.

“…It is interesting to note, though, that concerted mechanistic models for related metal‐catalyzed hydroaminations have been proposed,66 which essentially correspond to the proton‐switch mechanism in Scheme , if H of the first RXH is replaced by a metal (M). In a final example, Luo and coworkers have speculated that an asymmetric organocatalytic Michael addition of indoles to unsaturated aldehydes involves a hydrogen‐bond network including a single water molecule in the rate‐limiting proton transfer step 67. Apparently, the small amounts of water present in regular organic solvents were often sufficient to provide this water molecule.…”

Section: Discussionmentioning

confidence: 99%

Inner Workings of a Cinchona Alkaloid Catalyzed Oxa‐Michael Cyclization: Evidence for a Concerted Hydrogen‐Bond‐Network Mechanism

Hintermann

Ackerstaff

Boeck

2013

Cinchona alkaloids catalyze the oxa-Michael cyclization of 4-(2-hydroxyphenyl)-2-butenoates to benzo-2,3-dihydrofuran-2-yl acetates and related substrates in up to 99% yield and 91% ee (ee = enantiomeric excess). Catalyst and substrate variation studies reveal an important role of the alkaloid hydroxy group in the reaction mechanism, but not in the sense of a hydrogen-bonding activation of the carbonyl group of the substrate as assumed by the Hiemstra-Wynberg mechanism of bifunctional catalysis. Deuterium labeling at C-2 of the substrate shows that addition of RO-H to the alkenoate occurs with syn diastereoselectivity of ≥99:1, suggesting a mechanism-based specificity. A concerted hydrogen-bond network mechanism is proposed, in which the alkaloid hydroxy group acts as a general acid in the protonation of the α-carbanionic center of the product enolate. The importance of concerted hydrogen-bond network mechanisms in organocatalytic reactions is discussed. The relative stereochemistry of protonation is proposed as analytical tool for detecting concerted addition mechanisms, as opposed to ionic 1,4-additions.