Palladium-Catalyzed C−H Functionalization of Phenyl 2-Pyridylsulfonates

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Divergent reactivities of 2-pyridyl sulfonate esters. Exceptionally mild access to alkyl bromides and 2-substituted pyridines

A series of 2- and 3-pyridyl sulfonate and tosylate esters of primary and secondary alcohols were synthesized and evaluated in the bromination reaction with MgBr2·Et2O. The greater coordinating ability of the 2-pyridyl sulfonate esters accounted for its observed superior reactivity and selectivity. Reaction of neopentyl and phenyl 2-pyridyl sulfonates with a variety of aryl and heteroaryl Li reagents led to 2-substituted pyridines at temperatures as low as −78 °C via an SNAr process. Mechanistic considerations are discussed.

Study on Palladium(II)-Catalyzed Mono-1-alkenylation of 9H-Carbazoles

A general and efficient method is reported for the direct mono-1-alkenylation of 9H-carbazole molecules with divalent palladium as a catalyst and an N-(2-pyridyl)sulfanyl directing group. This method also provides an efficient synthetic route for the synthesis of cross-dialkenylated carbazoles.

Rhodium(III)-Catalyzed Oxidative ortho-Olefination of Phenyl Carbamates with Alkenes: Elucidation of Acceleration Mechanisms by Using an Unsubstituted Cyclopentadienyl Ligand

It has been established that an unsubstituted cyclopentadienyl (Cp) Rh(III) complex is an effective catalyst for the oxidative ortho-olefination of phenyl carbamates with both acrylates and styrenes under mild conditions. In addition, diolefination of a protected BINOL (1,1'-binaphthalene-2,2'-diol) proceeded in high yields and disubstituted acrylates could participate in this catalysis. Experimental and theoretical mechanistic studies elucidated that an electron-deficient nature of the unsubstituted CpRh(III) complex accelerates both the electrophilic aryl C-H rhodation and the rate-limiting alkene insertion steps.

Transition Metal-Catalyzed Directing-Group-Assisted C-H Activation of Phenols

Strategies that exploit directing groups to control the site selectivity in the C-H activation of arenes have received much attention during the past two decades. In light of the importance of phenol derivatives in the areas of pharmaceuticals, agrochemicals, and materials science, transition-metal-catalyzed C-H activation of phenols has proven to be an extremely useful tool in organic synthesis. This Minireview summarizes the current state-of-the-art direct C-H activation of phenol derivatives under transition-metal catalysis.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.