Alcohols as Fluoroalkyl Synthons: Ni-catalyzed Dehydrogenative Approach to Access Polyfluoroalkyl Bis-indoles

BINAP-CuH-catalysed enantioselective allylation using alkoxyallenes to access 1,2-syn-tert,sec-diols

Herein, we present an economical method for highly enantioselective and diastereoselective Cu-BINAP-catalysed reductive coupling of alkoxyallenes with a range of electronically and structurally diverse ketones to afford 1,2-syn-tert,sec-diols, using PMHS as the hydride source. This reductive coupling has also been efficiently employed in the enantioselective desymmetrization of prochiral cyclic ketones harboring quaternary centres, in high yields with exclusive diastereoselectivity. Density Functional Theory (DFT) calculations are used to elucidate that the reaction is facilitated by a kinetically favourable "open" Z-enolate copper-alkoxyallene conformer, occurring at a lower Gibbs free energy barrier (by 3.9 kcal mol-1) than its E-enolate counterpart, dictating the stereoselectivity. Subsequently, this Z-enolate conformer synchronizes with appropriate nucleophilic faces to achieve the targeted syn-diastereoselectivity in the product through six-membered chair-like transition states during ketone addition.

Sequential One-Pot Transformation to R-CF2-Embedded 1,5-Diketones Enabled by Nickel: Access to 4-Perfluoroalkylpyridines

Herein, we have demonstrated the application of bench-stable polyfluorinated alcohols as fluoroalkylating reagents for a sequential one-pot transformation with ketones to R-CF2-embedded 1,5-diketones and pyridines enabled by a nickel catalyst. The protocol is tolerant to a range of functional groups (>31 examples and up to 85% yield) and perfluoro alcohols and releases H2 and H2O as byproducts. Preliminary mechanistic studies, EPR analyses, and deuterium scrambling experiments were performed, and observed PC-H/PC-D = 2.12.

Manganese catalyzed chemo-selective synthesis of acyl cyclopentenes: a combined experimental and computational investigation

Cyclopentenes serve as foundational structures in numerous natural products and pharmaceuticals. Consequently, the pursuit of innovative synthetic approaches to complement existing protocols is of paramount importance. In this context, we present a novel synthesis route for acyl cyclopentenes through a cascade reaction involving an acceptorless-dehydrogenative coupling of cyclopropyl methanol with methyl ketone, followed by a radical-initiated ring expansion rearrangement of the in situ formed vinyl cyclopropenone intermediate. The reaction, catalyzed by an earth-abundant metal complex, occurs under milder conditions, generating water and hydrogen gas as byproducts. Rigorous control experiments and detailed computational studies were conducted to unravel the underlying mechanism. The observed selectivity is explained by entropy-driven alcohol-assisted hydrogen liberation from an Mn-hydride complex, prevailing over the hydrogenation of unsaturated cyclopentenes.

Alcohols as Substrates in Transition-Metal-Catalyzed Arylation, Alkylation, and Related Reactions

Alcohols are abundant and attractive feedstock molecules for organic synthesis. Many methods for their functionalization require them to first be converted into a more activated derivative, while recent years have seen a vast increase in the number of complexity-building transformations that directly harness unprotected alcohols. This Review discusses how transition metal catalysis can be used toward this goal. These transformations are broadly classified into three categories. Deoxygenative functionalizations, representing derivatization of the C-O bond, enable the alcohol to act as a leaving group toward the formation of new C-C bonds. Etherifications, characterized by derivatization of the O-H bond, represent classical reactivity that has been modernized to include mild reaction conditions, diverse reaction partners, and high selectivities. Lastly, chain functionalization reactions are described, wherein the alcohol group acts as a mediator in formal C-H functionalization reactions of the alkyl backbone. Each of these three classes of transformation will be discussed in context of intermolecular arylation, alkylation, and related reactions, illustrating how catalysis can enable alcohols to be directly harnessed for organic synthesis.

Structurally divergent enantioselective synthesis of benzofuran fused azocine derivatives and spiro-cyclopentanone benzofurans enabled by sequential catalysis

An important objective in organic synthesis and medicinal chemistry is the capacity to access structurally varied and complex molecules rapidly and affordably from easily available starting materials. Herein, a protocol for the structurally divergent synthesis of benzofuran fused azocine derivatives and spiro-cyclopentanone benzofurans has been developed via chiral bifunctional urea catalyzed reaction between aurone-derived α,β-unsaturated imine and ynone followed by switchable divergent annulation reactions by Lewis base catalysts (DBU and PPh3) with concomitant epimerization. The skeletally diversified products were formed in high yields with high diastereo- and enantioselectivities. Computational analysis with DFT and accurate DLPNO-CCSD(T) has been employed to gain deeper insights into mechanistic intricacies and investigate the role of chiral and Lewis base catalysts in skeletal diversity.

Catalyst-free electrochemical trifluoromethylation of coumarins using CF3SO2NHNHBoc as the CF3 source

An efficient electrochemical trifluoromethylation of coumarins using CF₃SO₂NHNHBoc as the source of the trifluoromethyl group was developed. Under catalyst-free and external oxidant-free electrolysis conditions, a range of 3-trifluoromethyl coumarins were obtained in moderate to good yields. The method could be easily scaled up with moderate efficiency.

Zn(II)-Catalyzed Selective N-Alkylation of Amines with Alcohols Using Redox Noninnocent Azo-Aromatic Ligand as Electron and Hydrogen Reservoir

We report a sustainable and eco-friendly approach for selective N-alkylation of various amines by alcohols, catalyzed by a well-defined Zn(II)-catalyst, Zn(L^a)Cl₂ (1a), bearing a tridentate arylazo scaffold. A total of 57 N-alkylated amines were prepared in good to excellent yields, out of which 17 examples are new. The Zn(II)-catalyst shows wide functional group tolerance, is compatible with the synthesis of dialkylated amines via double N-alkylation of diamines, and produces the precursors in high yields for the marketed drugs tripelennamine and thonzonium bromide in gram-scale reactions. Control reactions and DFT studies indicate that electron transfer events occur at the azo-chromophore throughout the catalytic process, which shuttles between neutral azo, one-electron reduced azo-anion radical, and two-electron reduced hydrazo forms acting both as electron and hydrogen reservoir, enabling the Zn(II)-catalyst for N-alkylation reaction.

Tertiary Amides as Fluoroalkyl Aldehyde Surrogates: Access to meso-Fluorinated Bis(heteroaryl)methanes

Tertiary, morpholine-derived, fluoroalkyl amides have been found to be efficient, readily accessible, bench-stable surrogates of fluoroalkyl aldehydes. This discovery is applied to the one-pot synthesis of a symmetrical and, more challengingly, unsymmetrical meso-fluoroalkylated bis(heteroaryl)methanes via a Schwartz's reagent-mediated reductive activation. The usefulness of this approach for the introduction of a fluoromethylated carbon bridge was proven by implementation of the developed methodology in the synthesis of a fluorine-decorated bispyrromethane skeleton and an α-alkylated BODIPY core.

Regio-Selective C3- and N-Alkylation of Indolines in Water under Air Using Alcohols

We disclosed a regio-selective C-H and N-H bond functionalization of indolines using alcohols in water via tandem dehydrogenation of N-heterocycles and alcohols. A diverse range of N- and C3-alkylated indolines/indoles were accessed utilizing a new cooperative iridium catalyst. The practical applicability of this methodology was demonstrated by the preparative-scale synthesis and synthesis of a psychoactive drug, N,N-dimethyltryptamine. A catalytic cycle is proposed based on several kinetic experiments, series of control experiments and density functional theory calculations.

Recent advances in nickel-catalyzed C-C and C-N bond formation via HA and ADC reactions

In recent times, earth-abundant 3d-transition-metal catalysts have attracted much attention in contemporary catalysis. They have been widely employed as suitable alternatives to their counterparts noble metals. In particular, nickel catalysts provide distinctive redox properties; thus, their efficiency in sustainable organic transformations is manifold. In this review article, recent advances in nickel-catalyzed hydrogen auto-transfer (HA) and acceptorless dehydrogenative coupling (ADC) reactions for the construction of C-C and C-N bonds have been discussed.