Catalysts for Cross-Coupling Reactions with Non-activated Alkyl Halides

Cu-Catalyzed tertiary alkylation of α-(trifluoromethyl)styrenes with tertiary alkylmagnesium reagents

An efficient method for the synthesis of 3-tertiary alkylated 1,1-difluorostyrene derivatives via Cu-catalyzed alkylation of α-(trifluoromethyl)styrenes with tertiary alkylmagnesium reagents at room temperature was developed.

A nano-catalytic approach for C–B bond formation reactions

Nanoparticle-catalysed borylation is one of the most convenient methods for the synthesis of organoboranes to overcome the confines of homogeneous catalysis such as recyclability and heavy metal contamination.

Pronounced effect of pore dimension of silica support on Pd-catalyzed Suzuki coupling reaction under ambient conditions

The pore size of the mesoporous silica support affects the reactivity of heterogeneous palladium catalysts in the Suzuki reaction under ambient conditions, which is leveled at higher temperature.

Cobalt-catalyzed C(sp3)–H/C(sp2)–H oxidative coupling between alkanes and benzamides

A direct cobalt-catalyzed oxidative coupling between C(sp²)–H in unactivated benzamides and C(sp³)–H in simple alkanes, ethers and toluene derivatives was explored.

Striving to exploit alkyl electrophiles: challenge and choice in transition metal-catalyzed cross-coupling reactions of sulfones

Transition metal-catalyzed cross-coupling reactions of alkyl sulfones as crystalline and readily available alkyl electrophiles via a radical process are highlighted.

Visible-Light-Driven Palladium-Catalyzed Radical Alkylation of C-H Bonds with Unactivated Alkyl Bromides

Reported herein is a novel visible-light photoredox system with Pd(PPh₃ )₄ as the sole catalyst for the realization of the first direct cross-coupling of C(sp³ )-H bonds in N-aryl tetrahydroisoquinolines with unactivated alkyl bromides. Moreover, intra- and intermolecular alkylations of heteroarenes were also developed under mild reaction conditions. A variety of tertiary, secondary, and primary alkyl bromides undergo reaction to generate C(sp³ )-C(sp³ ) and C(sp² )-C(sp³ ) bonds in moderate to excellent yields. These redox-neutral reactions feature broad substrate scope (>60 examples), good functional-group tolerance, and facile generation of quaternary centers. Mechanistic studies indicate that the simple palladium complex acts as the visible-light photocatalyst and radicals are involved in the process.

Palladium-Catalyzed Carbocyclizations of Unactivated Alkyl Bromides with Alkenes Involving Auto-tandem Catalysis

The development of a general catalytic system for the palladium-catalyzed carbocyclization of unactivated alkyl bromides with alkenes is described. This approach uses a commercially available bisphosphine ligand and avoids the use of carbon monoxide atmosphere present in prior studies involving alkyl iodides. Detailed mechanistic studies of the transformation are performed, which are consistent with auto-tandem catalysis involving atom-transfer radical cyclization followed by catalytic dehydrohalogenation. These studies also suggest that reactions involving alkyl iodides may proceed through a metal-initiated, rather than metal-catalyzed, radical chain process.

Radiosynthesis of 1-iodo-2-[11 C]methylpropane and 2-methyl-1-[11 C]propanol and its application for alkylation reactions and C-C bond formation

The multitude of biologically active compounds requires the availability of a broad spectrum of radiolabeled synthons for the development of positron emission tomography (PET) tracers. The aim of this study was to synthesize 1-iodo-2-[¹¹ C]methylpropane and 2-methyl-1-[¹¹ C]propanol and investigate the use of these reagents in further radiosynthesis reactions. 2-Methyl-1-[¹¹ C]propanol was obtained with an average radiochemical yield of 46 ± 6% d.c. and used with fluorobenzene as starting material. High conversion rates of 85 ± 4% d.c. could be observed with HPLC, but large precursor amounts (32 mg, 333 μmol) were needed. 1-Iodo-2-[¹¹ C]methylpropane was synthesized with a radiochemical yield of 25 ± 7% d.c. and with a radiochemical purity of 78 ± 7% d.c. The labelling agent 1-iodo-2-[¹¹ C]methylpropane was coupled to thiophenol, phenol and phenylmagnesium bromide. Average radiochemical conversions of 83% d.c. for thiophenol, 40% d.c. for phenol, and 60% d.c. for phenylmagnesium bromide were obtained. In addition, [¹¹ C]2-methyl-1-propyl phenyl sulphide was isolated with a radiochemical yield of 5 ± 1% d.c. and a molar activity of 346 ± 113 GBq/μmol at the end of synthesis. Altogether, the syntheses of 1-iodo-2-[¹¹ C]methylpropane and 2-methyl-1-[¹¹ C]propanol were achieved and applied as proof of their applicability.

Methods Utilizing First-Row Transition Metals in Natural Product Total Synthesis

First-row transition-metal-mediated reactions constitute an important and growing area of research due to the low cost, low toxicity, and exceptional synthetic versatility of these metals. Currently, there is considerable effort to replace existing precious-metal-catalyzed reactions with first-row analogs. More importantly, there are a plethora of unique transformations mediated by first-row metals, which have no classical second- or third-row counterpart. Herein, the application of first-row metal-mediated methods to the total synthesis of natural products is discussed. This Review is intended to highlight strategic uses of these metals to realize efficient syntheses and highlight the future potential of these reagents and catalysts in organic synthesis.

Decarboxylative alkenylation

Olefin chemistry, through pericyclic reactions, polymerizations, oxidations, or reductions, plays an essential role in the foundation of how organic matter is manipulated.¹ Despite its importance, olefin synthesis still largely relies upon chemistry invented more than three decades ago, with metathesis² being the most recent addition. Here we describe a simple method to access olefins with any substitution pattern or geometry from one of the most ubiquitous and variegated building blocks of chemistry: alkyl carboxylic acids. The same activating principles used in amide-bond synthesis can thus be employed, under Ni- or Fe-based catalysis, to extract CO₂ from a carboxylic acid and economically replace it with an organozinc-derived olefin on mole scale. Over sixty olefins across a range of substrate classes are prepared, and the ability to simplify retrosynthetic analysis is exemplified with the preparation of sixteen different natural products across a range of ten different families.

Convenient and General Zinc-Catalyzed Borylation of Aryl Diazonium Salts and Aryltriazenes under Mild Conditions

A convenient and general zinc‐catalyzed borylation of aryl diazonium salts and aryltriazenes has been developed. With bis‐ (pinacolato)diboron as the borylation reagent, aryldiazonium tetrafluoroborate salts and aryltriazenes were transformed into the corresponding arylboronates in moderate to excellent yields under mild conditions. As a convenient and practical methodology, no additional ligands, base, or any other additives are required here.

A photoinduced reaction of perfluoroalkyl halides with 1,3-diarylprop-2-yn-1-ones catalyzed by DABSO

The sulfur dioxide surrogate of DABCO·(SO₂)₂ is used as an efficient catalyst for the cleavage of the perfluoroalkyl-halogen bond under visible-light irradiation. A plausible mechanism supported by theoretical calculations is proposed.

Acylboranes: synthetic strategies and applications

Acylboranes are an attractive class of compounds, of which the synthesis has very recently been documented as summarised in this review. Access to these compounds provides a path to study their properties and reactivity.

An immobilized symmetrical bis-(NHC) palladium complex as a highly efficient and recyclable Suzuki–Miyaura catalyst in aerobic aqueous media

A novel palladium-silica complex was prepared and characterized. This complex is a highly efficient and easily recyclable catalyst for Suzuki–Miyaura cross-coupling reaction under mild aqueous conditions, and can be reused efficiently up to 6 consecutive runs.

Oxidative C-C Bond Formation Reactivity of Organometallic Ni(II), Ni(III), and Ni(IV) Complexes

The use of the tridentate ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me₃tacn) and the cyclic alkyl/aryl C-donor ligand -CH₂CMe₂-o-C₆H₄- (cycloneophyl) allows for the synthesis of isolable organometallic Ni^II, Ni^III, and Ni^IV complexes. Surprisingly, the five-coordinate Ni^III complex is stable both in solution and the solid state, and exhibits limited C-C bond formation reactivity. Oxidation by one electron of this Ni^III species generates a six-coordinate Ni^IV complex, with an acetonitrile molecule bound to Ni. Interestingly, illumination of the Ni^IV complex with blue LEDs results in rapid formation of the cyclic C-C product at room temperature. This reactivity has important implications for the recently developed dual Ni/photoredox catalytic systems proposed to involve high-valent organometallic Ni intermediates. Additional reactivity studies show the corresponding Ni^II species undergoes oxidative addition with alkyl halides, as well as rapid oxidation by O₂, to generate detectable Ni^III and/or Ni^IV intermediates and followed by C-C bond formation.

A triazine-based Ni(II) PNP pincer complex as catalyst for Kumada-Corriu and Negishi cross-coupling reactions

ABSTRACT

Kumada-Corriu and Negishi cross-coupling reactions, catalyzed efficiently by a Ni(II) PNP pincer complex containing a triazine backbone, are described. The catalyst is able to react with both activated and inactivated aryl halides including chlorides as well as phenol derivatives such as tosylates and mesylates to give the corresponding cross-coupling products in good to excellent isolated yields. A high diversity of substrates was tested under moderate conditions for both types of reactions.

GRAPHICAL ABSTRACT

Cobalt-Catalyzed Reductive Cross-Coupling Between Styryl and Benzyl Halides

A simple and efficient protocol for the direct reductive cross-coupling between alkenyl and benzyl halides using a Co/Mn system has been developed. This reaction proceeds smoothly in the presence of [CoBr₂ (PPh₃ )₂ ] as the catalyst, with NaI as an additive in acetonitrile with a broad scope of functionalized alkenyl and benzyl halides. Different functional groups are tolerated on both coupling partners, thus, significantly extending the general scope of transition-metal-catalyzed benzylation of alkenyl halides. Moderate to excellent yields were also obtained. From a mechanistic point of view, a radical chain mechanism was proposed. This reaction is stereospecific and some studies suggest the retention of the double-bond configuration.

Radicals: Reactive Intermediates with Translational Potential

This Perspective illustrates the defining characteristics of free radical chemistry, beginning with its rich and storied history. Studies from our laboratory are discussed along with recent developments emanating from others in this burgeoning area. The practicality and chemoselectivity of radical reactions enable rapid access to molecules of relevance to drug discovery, agrochemistry, material science, and other disciplines. Thus, these reactive intermediates possess inherent translational potential, as they can be widely used to expedite scientific endeavors for the betterment of humankind.

Palladium-Catalyzed Cross Coupling of Secondary and Tertiary Alkyl Bromides with a Nitrogen Nucleophile

We report a new class of catalytic reaction: the thermal substitution of a secondary and or tertiary alkyl halide with a nitrogen nucleophile. The alkylation of a nitrogen nucleophile with an alkyl halide is a classical method for the construction of C-N bonds, but traditional substitution reactions are challenging to achieve with a secondary and or tertiary alkyl electrophile due to competing elimination reactions. A catalytic process could address this limitation, but thermal, catalytic coupling of alkyl halides with a nitrogen nucleophile and any type of catalytic coupling of an unactivated tertiary alkyl halide with a nitrogen nucleophile are unknown. We report the coupling of unactivated secondary and tertiary alkyl bromides with benzophenone imines to produce protected primary amines in the presence of palladium ligated by the hindered trialkylphosphine Cy₂t-BuP. Mechanistic studies indicate that this amination of alkyl halides occurs by a reversible reaction to form a free alkyl radical.