Diversity-oriented synthesis of 1,2,3,5-tetrahydrobenzo[e][1,2,4]oxadiazepines and 2,3-dihydro-1H-benzo[e][1,2,4]triazepines by base-induced [4 + 3] annulation reactions

Base-Mediated Tandem [3 + 2] Cycloaddition/Ring Openning Reaction of Arylhydrazonoyl Chlorides with Arylnitroso Compounds for Synthesis of Substituted Diazene Oxides

A base-mediated tandem [3 + 2] cycloaddition/ring opening reaction of nitrilimines generated from arylhydrazonoyl chlorides with arylnitroso compounds has been developed. This protocol provides a novel and rapid approach for the synthesis of substituted azoxy compounds under mild conditions with moderate to good yields and a broad substrate scope.

Synthesis of Functionalized Tetrahydroquinoline Containing Indole Scaffold via Chemoselective Annulation of Aza-ortho-quinone Methide Precursor

The chemoselective annulation of aza-ortho-quinone methide generated by in situ o-chloromethyl sulfonamide has been achieved with bifunctional acyclic olefin. This efficient approach provides access to the diastereoselective synthesis of functionalized tetrahydroquinoline derivatives containing indole scaffolds through the inverse-electron-demand aza-Diels-Alder reaction under mild reaction conditions with excellent results (up to 93% yield, > 20:1 dr). Moreover, this article realized the cyclization of α-halogeno hydrazone with electron-deficient alkene affording the tetrahydropyridazine derivatives, which had never been reported.

Synthesis of 1,3,5-trisubstituted pyrazoles via 1,3-dipolar cycloaddition of nitrile imines with ninhydrin-derived Morita-Baylis-Hillman carbonates

An effective synthetic method for 1,3,5-trisubstituted pyrazoles via 1,3-dipolar cycloaddition reaction has been developed. This reaction could smoothly proceed between ninhydrin-derived Morita-Baylis-Hillman carbonates and nitrilimines to provide a wide scope of differently substituted pyrazoles in high yields (up to 95%). In addition, the reaction mechanism was also proposed to explain its regioselectivity.

[4+n] Annulation Reactions Using ortho-Chloromethyl Anilines as Aza-ortho-Quinone Methide Precursors

Aza-ortho-quinone methides are important reactive intermediates that have found broad applications in synthetic chemistry. Recently, 1,4-elimination of ortho-chloromethyl aniline derivatives has emerged as a novel, powerful and convenient method for aza-ortho-quinone methide generation. This review will highlight the recent applications of aza-ortho-quinone methide precursors in annulation reactions to access various biologically important nitrogen-containing heterocycles. The general mechanisms are briefly discussed as well.

1 Introduction

2 [4+n] Annulation Reactions Using ortho-Chloromethyl Anilines as Aza-ortho-Quinone Methide Precursors

2.1 [4+2] Annulation Reactions

2.2 [4+1] Annulation Reactions

2.3 [4+3] Annulation Reactions

3 Conclusion and Perspective

Base-mediated unprecedented tandem cyclization reaction of nitrilimines and sulfur ylides: facile approaches to multifunctionalized pyrazolines

An interesting three-component tandem reaction between hydrazonoyl chlorides and α-keto-derived sulfonium salts is reported. Highly substituted pyrazolines were obtained in moderate to excellent yield under mild conditions. Moreover, α-keto-stabilised sulfur...

Synthesis of Benzo[e][1,4]thiazepines by Base-Induced Formal [4+3] Annulation Reaction of Aza-o-quinone Methides and Pyridinium 1,4-Zwitterionic Thiolates

The base-induced formal [4+3] annulation reaction of in situ-formed aza-o-quinone methides and pyridinium 1,4-zwitterionic thiolates is reported. This protocol provides a novel and reliable method for the synthesis of biologically interesting benzo[e][1,4]thiazepine derivatives in synthetically useful yields. In addition, postsynthetic modification results in the formation of its sulfoxide and sulfone derivatives.

(4 + 2) cyclization of aza-o-quinone methides with azlactones: construction of biologically important dihydroquinolinone frameworks

A base-promoted (4 + 2) cyclization of aza-o-quinone methides (aza-o-QMs) in situ generated from N-(o-chloromethyl)aryl amides was established. In this approach, azlactones were utilized as competent two-atom reaction partners to undergo (4 + 2) cyclization with aza-o-QMs, which afforded a series of dihydroquinolinone derivatives in overall good yields (up to 98%). This protocol has not only advanced the development of aza-o-QM-involved reactions, but also offered a useful method for constructing biologically important dihydroquinolinone frameworks.

Synthesis of spiro[4.4]thiadiazole derivatives via double 1,3-dipolar cycloaddition of hydrazonyl chlorides with carbon disulfide

An operationally simple and convenient synthesis method toward a series of diverse spiro[4.4]thiadiazole derivatives via double [3 + 2] 1,3-dipolar cycloaddition of nitrilimines generated in situ from hydrazonyl chlorides with carbon disulfide has been achieved under mild reaction conditions.

A simple and convenient synthesis method for spiro[4.4]thiadiazole derivatives via double [3 + 2] 1,3-dipolar cycloaddition of nitrilimines generated in situ from hydrazonyl chlorides with carbon disulfide has been achieved.

Synthesis of Bicyclo[4.1.0]tetrahydropyridazines by a Sequential [4 + 2] and [1 + 2] Annulation Reaction of Azoalkenes and Crotonate-Derived Sulfur Ylides

The base-induced unprecedented tandem [4 + 2] and [1 + 2] annulation reaction of in situ formed 1,2-diaza-1,3-dienes and crotonate-derived sulfur ylides is reported. This protocol provides a novel and practical method for the synthesis of cyclopropane-fused tetrahydropyridazines with a quaternary carbon center in synthetically useful yield. In this tandem reaction, three new bonds were formed in one pot, and the crotonate-derived sulfur ylide serves as a C3 synthon.