N-Heterocyclic carbene based catalytic platform for Hauser-Kraus annulations

NHC-Catalyzed Formal [4 + 2] Annulation of o-Formyl-Tethered Michael Acceptors and Ynones to Access Highly Functionalized Naphthalene Derivatives

Herein we demonstrate a novel organocatalytic method to access multifunctionalized naphthalenes via an NHC-catalyzed reaction of ynones and o-formyl-tethered Michael acceptors. The presented method proceeds through an intermolecular Stetter reaction-cyclization-aromatization cascade and represents a rare example of organocatalytic benzannulation for the synthesis of substituted arenes by using ynone as a two-carbon synthon. The current method has broad substrate scope; postsynthetic transformations and gram-scale syntheses highlight the practicality of the displayed methodology.

DBU-Mediated Isomerization/6-π Electro-Cyclization/Oxidation Cascade of Sulfonyl-Substituted Allenyl Ketones for the Construction of Hetero-1,3,5-Trisubstituted Benzene

1,3,5-tri-substituted benzene rings emerged with unique properties has widespread applications in materials, boosting the rapid development of their synthesis. Despite the significance, the direct construction of hetero-1,3,5-trisubstituted benzene core was far less-developed. Herein, we realized a DBU-mediated isomerization/6-π electro-cyclization/oxidative aromatization cascade of sulfonyl-substituted allenyl ketones under an air atmosphere (DBU=1,8-diazabicyclo[5.4.0]undec-7-ene). This versatile protocol featured metal-free conditions, easy operation, and broad functional group tolerance provides a new avenue for the construction of hetero-1,3,5-tri-substituted benzene.

A Benzannulation Strategy for Rapid Access to Quinazoline-2,4-diones via Oxidative N-Heterocyclic Carbene Catalysis

N-Heterocyclic carbene-catalyzed formal [4+2] benzannulation of enals with suitably substituted pyrimidine-2,4-diones allowing the mild and facile synthesis of functionalized quinazoline-2,4-diones is presented. This oxidative transformation proceeds via the simultaneous generation of dienolates and α,β-unsaturated acylazoliums and follows a vinylogous Michael/aldol/β-lactonization/decarboxylation/oxidation sequence to afford quinazoline-2,4-diones, including axially chiral ones with suitable substitutions, in an operationally simple procedure. In addition, substituted coumarins as dienolate precursors afforded benzochromen-6-one derivatives.

Recent Progress towards Organocatalyzed Asymmetric (Hetero)Arene Formation

Owing to the importance of arene moieties in organic chemistry, methods for arene construction attract great attention. Besides the traditional substitution strategy from pre-existing arenes, the straightforward formation of arene cores can also provide significant shortcuts towards a wide array of target molecules with different substitution patterns. Among direct arene formation reactions, applying environmentally benign organocatalysis to access arene moieties continues to attract increasing attention. This short review provides a brief summary of recent progress on organocatalyzed de novo (hetero)arene formation and applications in enantioselective synthesis.

1 Introduction

2 Arene Formation with Non-Covalent Organocatalysts

2.1 Arene Formation with Acid Organocatalysts

2.2 Arene Formation with Base Organocatalysts

2.3 Arene Formation with Hydrogen-Bonding Organocatalysts

3 Arene Formation with Covalent Organocatalysts

3.1 Arene Formation with Lewis Base Organocatalysts

3.1.1 Arene Formation with Secondary Amine Organocatalysts

3.1.2 Arene Formation with Tertiary Amine, Tertiary Phosphine and Sulfide Organocatalysts

3.1.3 Arene Formation with N-Heterocyclic Carbene Organocatalysts

3.2 Arene Formation with Lewis Acid Organocatalysts

4 Conclusion

Electroreductive Coupling of Phthalic Anhydrides with α,β-Unsaturated Carbonyl Compounds: Synthesis of 1,4-Dihydroxynaphthalenes

Electroreductive coupling of phthalic anhydrides with α,β-unsaturated carbonyl compounds in the presence of TMSCl and subsequent treatment with 1 M HCl gave 1,4-dihydroxynaphthalenes and 2-methyl-2,3-dihydronaphthalene-1,4-diones.