ABSTRACT
Herein we present the first example of aryl radical formation via the visible light-mediated decarboxylation of aryl carboxylic acids using photoredox catalysis. This method constitutes a mild protocol for the decarboxylation of cheap and abundant aryl carboxylic acids and tolerates both electron-rich substrates and those lacking ortho-substitution. The in situ formation of an acyl hypobromite is proposed to prevent unproductive hydrogen atom abstraction and trapping of the intermediate aroyloxy radical, enabling mild decarboxylation.
ABSTRACT
Organic reactions that involve the direct functionalization of non-activated C-H bonds represent an attractive class of transformations which maximize atom- and step-economy, and simplify chemical synthesis. Due to the high stability of C-H bonds, these processes, however, have most often required harsh reaction conditions, which has drastically limited their use as tools for the synthesis of complex organic molecules. Following the increased understanding of mechanistic aspects of C-H activation gained over recent years, great strides have been taken to design and develop new protocols that proceed efficiently under mild conditions and duly benefit from improved functional group tolerance and selectivity. In this review, we present the current state of the art in this field and detail C-H activation transformations reported since 2011 that proceed either at or below ambient temperature, in the absence of strongly acidic or basic additives or without strong oxidants. Furthermore, by identifying and discussing the major strategies that have led to these improvements, we hope that this review will serve as a useful conceptual overview and inspire the next generation of mild C-H transformations.
ABSTRACT
The synthesis and catalytic activity of long-chain NHC-stabilized RuNPs are presented. Full characterization of these novel nanostructures including surface state studies show that the ligand influences the number and the location of Ru active sites which impacts the NP catalytic activity, especially in hydrogenation reactions. The high stability and versatility of these nanosystems make them successful catalysts for both oxidation and hydrogenation reactions that can even be performed successively in a one pot-fashion.
ABSTRACT
The stereochemistry of gamma-butyrolactons tetrahydro-6a-phenylfuro[3,4-b]furan-2(3H)-one (1), 1,4,5,9b-tetrahydro-3a-methylnaphtho[2,1-b]furan-2(3aH)-one (2), 1,4,5,9 b-tetrahydro-3a-methylfuro[2,3-c]quinolin-2(3aH)-one (3) and hexahydro-furo[3,2-c]benzofuran-2-one (4) was studied using DPFGSE-NOE experiments. Compounds 1-3 contain two stereocenters, while 4 contains three. Both (1)H and (13)C spectra showed a single diastereomer of all the compounds. Routine 2D experiments (DQF)-COSY, HMQC/HSQC, and HMBC were used to assign (1)H and (13)C spectra completely. Diastereotopic methylene protons with resolved (1)H NMR signals as well as protons of cyclohexane served as references for the construction of the spatial arrangement in the molecules. NOE contacts between protons attached to the stereocenter and the diastereotopic protons were thus used to determine the configuration of the molecules. Vicinal coupling constants (3)J assisted the assignment of the conformational arrangement of the cyclohexane ring of 4.
Subject(s)
4-Butyrolactone/analogs & derivatives , 4-Butyrolactone/chemistry , Magnetic Resonance Spectroscopy/methods , Cyclization , Models, Molecular , Molecular Conformation , Molecular Structure , Protons , StereoisomerismABSTRACT
N-Heterocyclic carbenes (NHC) have become an important class of organocatalysts and class of ligands for transition-metal catalysis. In organocatalyzed umpolung reactions, thiazolium salt-derived NHC have been used successfully for decades. Even so, during recent years there has been an increased interest in NHC-catalyzed transformations and many new reactions have been developed. This article focuses on the use of NHC in the conjugate umpolung of alpha,beta-unsaturated aldehydes.
