Triflic anhydride mediated synthesis of 3,4-dihydroquinazolines: a three-component one-pot tandem procedure

Triflic Anhydride-Mediated Unprecedented Reactivities of Diacetonide Endoglucofuranose and Ribose Tetracetate: Direct Access to γ-Butenolides and Oxazoles

Herein, we present two unprecedented reactions for the synthesis of γ-butenolides and oxazoles, leveraging Tf2O's promoted reactivity of nitriles with diacetonide endoglucofuranose and 1,2,3,5-tetra-O-acetyl-β-d-ribofuranose. This method is highly efficient and straightforward and employs a one-step, metal-free protocol. It is effective with both aromatic and aliphatic nitriles and demonstrates a broad substrate scope. Our approach provides a versatile and practical pathway for the synthesis of structurally diverse compounds, significantly expanding the utility of Tf2O in synthetic chemistry.

Triflic Anhydride-Mediated Approach to Furo[3,2-b]furans from Diacetonide Protected Furanoses

Trifluoromethanesulfonic anhydride (Tf2O) exhibits excellent reactivity as an electrophile, serving as a highly versatile reagent in diverse chemical transformations. Herein, we report an operationally simple, efficient, unique, and practical one-step strategy for synthesizing diverse valuable structures bearing furo[3,2-b]furans core leveraging Tf2O's promoted reactivity of nitriles with diacetonide protected furanose. Furthermore, we demonstrate the potential of furo[3,2-b]furan as a precursor for complex structures through 1,3-dipolar cycloaddition.

Constructing new bonds to carbon in dihydroquinazolines via hypervalent iodine(III)-mediated C(sp3)-C(sp3) bond functionalization

A hypervalent iodine(III)-mediated C(sp3)-C(sp3) bond functionalization reaction for the formation of C-C, C-P, and C-H bonds in dihydroquinazolines has been developed. This one-pot method involves successive oxidation of dihydroquinazoline substrates, mesolytic cleavage of a tert-butyl substituent, and bond formation to a variety of nucleophiles in moderate to high yields.

Direct Formation of C-C, C-N, and C-O Bonds in Dihydroquinazolines via Hypervalent Iodine(III)-Mediated sp3 C-H Functionalization

A hypervalent iodine(III)-mediated cross-dehydrogenative coupling reaction for the direct formation of C-C, C-N, and C-O bonds in dihydroquinazolines has been developed. This one-pot method allows for the synthesis of C4-disubstituted dihydroquinazolines as well as C4-spirolactam, spirolactone, and spiroindene dihydroquinazolines in moderate to high yields.

Tf2O-Promoted Regioselective Heteronucleophilic Ring-Opening Approaches of Tetrahydrofuran

The ring-opening functionalization strategy in tetrahydrofuran (THF) represents an ideal approach to access different valuable structures. Herein, we report different operationally simple, efficient, unique, and practical regioselective heteronucleophilic ring-opening strategies for the THF system. Tf2O, which is a strong electrophilic activator, was found to generate a THF triflate intermediate that triggers the nucleophilicity of nitriles (Nu1) and led to regioselective ring opening in the presence of different nucleophiles (Nu2). Furthermore, the synthesis of different heteronucleophilic ring-opening dimerization products was attributed to the nucleophilicity of Nu2. We also demonstrated that use of borane-tetrahydrofuran (BTHF) can achieve challenging hydride addition in a similar manner.

Triflic Anhydride (Tf2O)-Activated Transformations of Amides, Sulfoxides and Phosphorus Oxides via Nucleophilic Trapping

Trifluoromethanesulfonic anhydride (Tf2O) is utilized as a strong electrophilic activator in a wide range of applications in synthetic organic chemistry, leading to the transient generation of a triflate intermediate. This versatile triflate intermediate undergoes nucleophilic trapping with diverse nucleophiles to yield novel compounds. In this review, we describe the features and applications of triflic anhydride in organic synthesis reported in the past decade, especially in amide, sulfoxide, and phosphorus oxide chemistry through electrophilic activation. A plausible mechanistic pathway for each important reaction is also discussed.

1 Introduction

2 Amide Chemistry

2.1 Carbon Nucleophiles

2.2 Hydrogen Nucleophiles

2.3 Nitrogen Nucleophiles

2.4 Oxygen and Sulfur Nucleophiles

2.5 hosphorus Nucleophiles

2.6 A Vilsmeier-Type Reagent

2.7 Umpolung Reactivity in Amides

3 Sulfoxide Chemistry

3.1 Oxygen Nucleophiles

3.2 Carbon Nucleophiles

3.3 Nitrogen Nucleophiles

3.4 Thionium Reagents

4 Phosphorus Chemistry

4.1 Hendrickson’s Reagent

4.2 Diaryl Phosphine Oxides

4.3 Phosphonates, Phosphates and Phosphinates

5 Conclusion and Outlook

Advances in Proteasome Enhancement by Small Molecules

The proteasome system is a large and complex molecular machinery responsible for the degradation of misfolded, damaged, and redundant cellular proteins. When proteasome function is impaired, unwanted proteins accumulate, which can lead to several diseases including age-related and neurodegenerative diseases. Enhancing proteasome-mediated substrate degradation with small molecules may therefore be a valuable strategy for the treatment of various neurodegenerative diseases such as Parkinson's, Alzheimer's, and Huntington's diseases. In this review, we discuss the structure of proteasome and how proteasome's proteolytic activity is associated with aging and various neurodegenerative diseases. We also summarize various classes of compounds that are capable of enhancing, directly or indirectly, proteasome-mediated protein degradation.

Chemoselective Reactions of Isocyanates with Secondary Amides: One-Pot Construction of 2,3-Dialkyl-Substituted Quinazolinones

A facile method for the preparation of 2,3-dialkyl-substituted quinazolinones from readily available N-arylamides and commercial isocyanates was developed. This one-pot procedure involves the chemoselective activation of the secondary amide with Tf₂O/2-Br-Pyr, the sequential addition of isocyanate, and cyclization. The mild reaction is general for a wide range of substrates and can be run on a gram scale.

Dihydroquinazolines enhance 20S proteasome activity and induce degradation of α-synuclein, an intrinsically disordered protein associated with neurodegeneration

Aggregates or oligomeric forms of many intrinsically disordered proteins (IDPs), including α-synuclein, are hallmarks of neurodegenerative diseases, like Parkinson's and Alzheimer's disease, and key contributors to their pathogenesis. Due to their disordered nature and therefore lack of defined drug-binding pockets, IDPs are difficult targets for traditional small molecule drug design and are often referred to as "undruggable". The 20S proteasome is the main protease that targets IDPs for degradation and therefore small molecule 20S proteasome enhancement presents a novel therapeutic strategy by which these undruggable IDPs could be targeted. The concept of 20S activation is still relatively new, with few potent activators having been identified thus far. Herein, we synthesized and evaluated a library of dihydroquinazoline analogues and discovered several promising new 20S proteasome activators. Further testing of top hits revealed that they can enhance 20S mediated degradation of α-synuclein, the IDP associated with Parkinson's disease.

Chemoselective α-Sulfidation of Amides Using Sulfoxide Reagents

The direct α-sulfidation of tertiary amides using sulfoxide reagents under electrophilic amide activation conditions is described. Employing convenient and readily available reagents, selective functionalization takes place to generate isolable sulfonium ions en route to α-sulfide amides. Mechanistic studies identified activated sulfoxides as promoters of the desired transformation and enabled the extension of the methodology from benzylic to aliphatic amide substrates.

A facile access to N-sulfonylthioimidates and their use for the transformation to 3,4-dihydroquinazolines

N-Sulfonylthioimidates can be efficiently synthesized through one-pot three-component coupling of terminal alkynes, sulfonyl azides, and thiols by using a copper(i) catalyst in the presence of 4-dimethylaminopyridine. The proposed reaction is characterized by mild reaction conditions and tolerance of diverse functional groups. Additionally, the crucial pharmacophore of 3,4-dihydroquinazolines was synthesized using a one-pot synthetic strategy from N-sulfonylthioimidates.

One-Pot Tandem Assembly of Amides, Amines, and Ketones: Synthesis of C4-Quaternary 3,4- and 1,4-Dihydroquinazolines

A multicomponent tandem assembly procedure for the synthesis of diverse C4-quaternary 3,4-dihydroquinazolines from amides, amines, and ketones has been developed. The one-pot reaction involves successive triflic anhydride mediated amide dehydration, ketimine addition, and Pictet-Spengler-like cyclization processes and affords products in up to 92% yield. Conversion of 3,4-dihydroquinazolines to the corresponding 1,4-dihydroquinazolines via a two-step N1 dealkylation and regioselective N3 functionalization protocol, including computational rationale for the observed regioselectivity, is also described.