Synthesis of C3-Substituted 1-Indenones Enabled by CuCl/Brønsted Acid Cooperative Catalysis.

Further correction for ‘Reductive annulations of arylidene malonates with unsaturated electrophiles using photoredox/Lewis acid cooperative catalysis’ by Rick C. Betori et al., Chem. Sci., 2019, 10, 3353–3359, https://doi.org/10.1039/C9SC00302A.

Correction for ‘Reductive annulations of arylidene malonates with unsaturated electrophiles using photoredox/Lewis acid cooperative catalysis’ by Rick C. Betori et al., Chem. Sci., 2019, 10, 3353–3359, DOI: 10.1039/C9SC00302A.

An effective carbonyl‐oxygen‐assisted transition‐metal‐free approach was developed for the one‐pot synthesis of 1,4‐diketones through the formal hydration of 4‐alkynones with complete regioselectivity under mild conditions. The reaction tolerates a wide range of functional groups, and the corresponding functionalized 1,4‐diketones were obtained in moderate to excellent yields (up to 94 %). Importantly, the complete regioselectivity was attributed to the fact that 2,3‐dihydrofuran intermediates were obtained as single products through the 5‐exo‐dig cyclization of 4‐alkynones; this was supported by control and isotope‐labeling experiments.

The interplay between metals and N-heterocyclic carbenes (NHCs) has provided a window of opportunities for the development of novel catalytic strategies within the past few years. The recent successful combination of Brønsted acids with NHCs has added a new dimension to the field of cooperative catalysis, enabling the stereoselective synthesis of functionalized pyrrolidin-2-ones as valuable scaffolds in heterocyclic chemistry. This Commentary will briefly highlight the concept of N-heterocyclic carbene/Brønsted acid cooperative catalysis as a new and powerful methodology in organic chemistry.

In this study, an organocatalytic ring-opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL) has been developed by employing PADIs as a novel and efficient acid/base bifunctional organocatalyst, which could afford metal-free poly(ϵ-caprolactone) with predictable molecular weight and narrow dispersity at a low catalyst loading under mild conditions. NMR and kinetic studies indicate that the ring-opening polymerizations of lactones catalyzed by PADIs proceed in a living and well controlled manner. Moreover, this organic Brønsted acid catalytic system could allow the synthesis of PCL with molecular weight above 60 kg/mol, as well as well-defined star polymers.

A convergent, organocatalytic asymmetric aminomethylation of α,β-unsaturated aldehydes by N-heterocyclic carbene (NHC) and (in situ generated) Brønsted acid cooperative catalysis is disclosed. The catalytically generated conjugated acid from the base plays dual roles in promoting the formation of azolium enolate intermediate, formaldehyde-derived iminium ion (as an electrophilic reactant), and methanol (as a nucleophilic reactant). This redox-neutral strategy is suitable for the scalable synthesis of enantiomerically enriched β(2) -amino acids bearing various substituents.

A convergent, organocatalytic asymmetric aminomethylation of α,β‐unsaturated aldehydes by N‐heterocyclic carbene (NHC) and (in situ generated) Brønsted acid cooperative catalysis is disclosed. The catalytically generated conjugated acid from the base plays dual roles in promoting the formation of azolium enolate intermediate, formaldehyde‐derived iminium ion (as an electrophilic reactant), and methanol (as a nucleophilic reactant). This redox‐neutral strategy is suitable for the scalable synthesis of enantiomerically enriched β2‐amino acids bearing various substituents.

The DFT perspective toward the [3 + 2] annulation reaction through NHC and Brønsted acid cooperative catalysis has been investigated.

Practical and regioselective brominations of aromatic compounds using tetrabutylammonium peroxydisulfate

Chiral Brønsted acid-catalyzed conjugate addition of indoles to azadienes: Enantioselective synthesis of hetero-triarylmethanes

A new, efficient, and inexpensive copper(II)/salicylic acid complex catalyzed Sonogashira-type cross-coupling of haloarenes and iodoheteroarenes with terminal alkynes

A simple and efficient synthesis of phenol biaryls by the cross‐couplings of quinone monoacetals (QMAs) and phenols is reported. The Brønsted acid catalytic system in 1,1,1,3,3,3‐hexafluoro‐2‐propanol was found to be particularly efficient for this transformation. This reaction can be extended to the synthesis of various phenol biaryls, including sterically hindered biaryls, with yields ranging from 58 to 90 % under mild reaction conditions and in a highly regiospecific manner.

A new, efficient, and inexpensive CuCl2/salicylic acid catalytic system has been developed to catalyze Sonogashira-type cross-coupling of haloarenes and iodoheteroarenes with terminal alkynes under mild reaction conditions to afford the corresponding coupling products in 18–95% yields. The role of salicylic acid might act as a bidentate O,O-donor ligand to activate the catalytic reactivity of copper chloride in coupling reactions was also briefly discussed.

A simple and efficient synthesis of phenol biaryls by the cross-couplings of quinone monoacetals (QMAs) and phenols is reported. The Brønsted acid catalytic system in 1,1,1,3,3,3-hexafluoro-2-propanol was found to be particularly efficient for this transformation. This reaction can be extended to the synthesis of various phenol biaryls, including sterically hindered biaryls, with yields ranging from 58 to 90 % under mild reaction conditions and in a highly regiospecific manner.

The hydration of β- and δ-hydroxy internal alkynes catalyzed by Hg(OTf)2 took place instantaneously to give ketones with complete regioselectivity under mild conditions, whereas the hydration of internal alkyne without hydroxy moiety was very slow and gave a mixture of ketones. If the hydroxy group is located more than five carbons from the triple bond it has no significant effect upon the hydration reaction.