P-Spiro phosphonium salts catalyzed asymmetric fluorination of 3-substituted benzofuran-2(3H)-ones

Lactone Enolates of Isochroman-3-ones and 2-Coumaranones: Quantification of Their Nucleophilicity in DMSO and Conjugate Additions to Chalcones

Owing to stereoelectronic effects, lactones often deviate in reactivity from their open-chain ester analogues as demonstrated by the CH acidity (in DMSO) of 3-isochromanone (pKa = 18.8) and 2-coumaranone (pKa = 13.5), which is higher than that of ethyl phenylacetate (pKa = 22.6). We have now characterized the reactivity of the lactone enolates derived from 3-isochromanone and 2-coumaranone by following the kinetics of their Michael reactions with p-quinone methides and arylidenemalonates (reference electrophiles) in DMSO at 20 °C. Evaluation of the experimentally determined second-order rate constants k2 by the Mayr-Patz equation, lg k2 = sN(N + E), furnished the nucleophilicity parameters N (and sN) of the lactone enolates. By localizing their position on the Mayr nucleophilicity scale, the scope of their electrophilic reaction partners becomes predictable, and we demonstrate a novel catalytic methodology for a series of carbon-carbon bond-forming reactions of lactone enolates with chalcones under phase transfer conditions in toluene.

Cyclic Dinucleotide-Based Enantioselective Fluorination in Water

The diverse structures of DNA serve as potent chiral scaffolds for DNA-based asymmetric catalysis, yet in most cases tens to hundreds of nucleotides in DNA hybrid catalysts hinder the deep insight into their structure-activity relationship. Owing to the structural simplicity and design flexibility of nucleotides, nucleotide-based catalysts have been emerging as a promising way to obtain fine structural information and understand the catalytic mechanisms. Herein, we found that a cyclic dinucleotide of cyclic di-AMP (c-di-AMP) and 1,10-phenanthroline copper(II) nitrate (Cu(phen)(NO₃)₂) are assembled to a c-di-AMP-based catalyst (c-di-AMP/Cu(phen)(NO₃)₂), which could fast achieve enantioselective fluorination in water with 90-99% yields and up to 90% enantiomeric excess (ee). The host-guest interaction between c-di-AMP and Cu(phen)(NO₃)₂ has been proposed mainly in a supramolecular interaction mode as evidenced by spectroscopic techniques of ultraviolet-visible, fluorescence, circular dichroism, and nuclear magnetic resonance. Cu(phen)(NO₃)₂ tightly binds to c-di-AMP with a binding constant of 1.7 ± 0.3 × 10⁵ M^-1, and the assembly of c-di-AMP/Cu(phen)(NO₃)₂ shows a modest rate enhancement to carbon-fluorine bond formations as supported by kinetic studies.

Nickel-catalyzed reductive monofluoroakylation of alkyl tosylate with bromofluoromethane to primary alkyl fluoride

A nickel-catalysed direct terminal monofluoromethlyation between alkyl tosylates and a low-cost, industrial raw material bromofluoromethane has been developed. This transformation has demonstrated high efficiency, mild conditions, and good functional-group compatibility. The key to success of this transformation lies in the ligand and mild base selection, ensuring the generation of various terminal monofluormethylation products.

Recent Advances on Benzofuranones: Synthesis and Transformation via C–H Functionalization

The benzofuranone structure is important in many fields, such as natural products, pharmaceuticals, building blocks, antioxidants, and dyes. The efficient synthesis and transformation of benzofuranones have attracted great attention in organic synthesis. They can be synthesized by the Friedel–Crafts reaction and intramolecular dehydration ring-closing and transition-metal-catalyzed reactions, among others. Their direct utilization in the preparation of other functional molecules further enhance their application. Due to their low pK a value and easy enolization, the transformation of benzofuranones via C(3)–H bond functionalization has been a hot issue since 2010. Herein, we highlight advances in the synthesis of benzofuranones and their transformation via C–H functionalization. Other transformations related to benzofuranones are also discussed.

1 Introduction

2 Synthesis of Benzofuranones

3 C–H Functionalization of Benzofuranones

4 Other Types of Reactions of Benzofuranones

5 Conclusion and Outlook

Diastereoselective α-Fluorination of N- tert-Butanesulfinyl Imidates

A diastereoselective α-fluorination of N- tert-butanesulfinyl imidates was developed. Deprotonation of N- tert-butanesulfinyl imidates with lithium hexamethyldisilazide generates aza-enolates that can be intercepted, with excellent diastereocontrol, by the inexpensive electrophilic fluorinating agent NFSI. This protocol was applied to the preparation of synthetically useful trans-2-fluoro-cyclohexamine with high enantiomeric purity (99.5% ee).

Modern Approaches for Asymmetric Construction of Carbon-Fluorine Quaternary Stereogenic Centers: Synthetic Challenges and Pharmaceutical Needs

New methods for preparation of tailor-made fluorine-containing compounds are in extremely high demand in nearly every sector of chemical industry. The asymmetric construction of quaternary C-F stereogenic centers is the most synthetically challenging and, consequently, the least developed area of research. As a reflection of this apparent methodological deficit, pharmaceutical drugs featuring C-F stereogenic centers constitute less than 1% of all fluorine-containing medicines currently on the market or in clinical development. Here we provide a comprehensive review of current research activity in this area, including such general directions as asymmetric electrophilic fluorination via organocatalytic and transition-metal catalyzed reactions, asymmetric elaboration of fluorine-containing substrates via alkylations, Mannich, Michael, and aldol additions, cross-coupling reactions, and biocatalytic approaches.

Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles

Chiral phase-transfer catalysis is one of the major catalytic principles in asymmetric catalysis. A broad variety of different catalysts and their use for challenging applications have been reported over the last decades. Besides asymmetric C–C bond forming reactions the use of chiral phase-transfer catalysts for enantioselective α-heterofunctionalization reactions of prochiral nucleophiles became one of the most important field of application of this catalytic principle. Based on several highly spectacular recent reports, we thus wish to discuss some of the most important achievements in this field within the context of this review.

Transition-Metal-Free Fluoroarylation of Diazoacetamides: A Complementary Approach to 3-Fluorooxindoles

An efficient transition-metal-free fluoroarylation reaction of N-aryl diazoacetamides with NFSI (N-fluorobenzenesulfonimide) is described. This reaction directly provides 3-fluorooxindole derivatives in yields of 67-93% with high selectivity via a carbene-free process under mild reaction conditions.

Organocatalytic asymmetric formal arylation of benzofuran-2(3H)-ones with cooperative visible light photocatalysis

An asymmetric arylation of benzofuran-2(3H)-ones with 1-naphthols has been developed through a cooperative visible light photocatalysis with asymmetric hydrogen-bond catalysis.

Highly enantioselective Michael addition reactions of 2-substituted benzofuran-3(2H)-ones to nitroolefins

A highly enantioselective Michael addition reaction of 2-substituted benzofuran-3(2H)-ones to nitroolefins was promoted by a bifunctional squaramide catalyst. As a result, a number of chiral 2,2'-substituted benzofuran-3-one derivatives, bearing adjacent quaternary-tertiary stereocenters, were efficiently synthesized with excellent enantioselectivities.

Propylphosphonium hydrogen carbonate ionic liquid supported on nano-silica as a reusable catalyst for the efficient multicomponent synthesis of fully substituted pyridines and bis-pyridines

An efficient method for the synthesis of fully substituted pyridines and bis-pyridines in the presence of propylphosphonium hydrogen carbonate supported on nano-silica (PPHC–nSiO₂) as a reusable catalyst under solvent-free conditions is reported.

Enantioselective Black rearrangement catalyzed by chiral bicyclic imidazole

A newly developed chiral imidazole nucleophilic catalyst, , was readily prepared and successfully applied to the enantioselective Black rearrangement with up to 88% ee for a wide range of substrates possessing different substituted groups. A plausible mechanism for the high enantioselectivity was proposed.