Catalyst-Free [3+2] Cycloaddition of Electron-Deficient Alkynes and o-Hydroxyaryl Azomethine Ylides in Water

Synthesis of Spiro[indoline-pyridine]-dicarboxylates and Substituted Alkylidene Oxindoles by Azomethine Ylides and MBH Carbonates of Isatins

We have developed an efficient protocol for the synthesis of spiro[indoline-pyridine]dicarboxylates and substituted alkylidene oxindoles through [3 + 3] cycloaddition and Michael addition individually by azomethine ylides and various MBH carbonates of isatins. The selective generation of cyclic products and chain products was achieved by changing the substituents at the 3-position of the oxindoles. The features of this method include convenient catalysts, mild reaction conditions, and broad substrate scopes.

Construction of 1,3,4-oxadiazolines bearing CF3-quaternary centers via amino-assisted [3 + 2] cycloadditions

An amino-assisted [3 + 2] cycloaddition strategy of nitrile imines with o-aminotrifluoroacetophenones has been explored, thus providing functionalized 1,3,4-oxadiazolines bearing CF3-quaternary centers in good to excellent yields in the presence of K2CO3 under mild conditions. The amino groups located at the ortho-position of trifluoroacetophenone might play a crucial role in the present cyclization. The MTT assay shows that the 1,3,4-oxadiazoline derivatives could be potential candidates for the treatment of head and neck cancers.

Recent Advances in Synthetic Routes to Azacycles

A heterocycle is an important structural scaffold of many organic compounds found in pharmaceuticals, materials, agrochemicals, and biological processes. Azacycles are one of the most common motifs of a heterocycle and have a variety of applications, including in pharmaceuticals. Therefore, azacycles have received significant attention from scientists and a variety of methods of synthesizing azacycles have been developed because their efficient synthesis plays a vital role in the production of many useful compounds. In this review, we summarize recent approaches to preparing azacycles via different methods as well as describe plausible reaction mechanisms.

One-pot catalyst-free synthesis of benzopyrroxazine derivatives by a mutually activated sequential annulation process

A one-pot catalyst-free reaction of o-hydroxyaryl azomethine ylides, vinyl pyridines and paraformaldehyde for the synthesis of benzopyrroxazines is reported, which offers a straightforward and atom-economical procedure for the preparation of benzopyrroxazine derivatives in moderate to excellent yields under mild conditions. A self-catalyzed [3 + 2] annulation through a mutual activation method and a sequential non-catalyzed [5 + 1] annulation process contribute to this strategy. The corresponding control experiments have been conducted to reveal the mechanism of this reaction.

Protecting Group-Dependent Synthesis of Densely Substituted Dihydropyrroles v/s Pyrroles via 5-Exo-trig Cascade Radical Cyclization to Alkynyl Vinylogous Carbamates

Densely substituted dihydropyrroles could be synthesized with excellent diastereoselectivity via 5-exo-trig cascade radical cyclization to alkynyl vinylogous carbamates. N-Alkyl/acyl protected alkynyl vinylogous carbamates upon radical cyclization using thiophenol gave substituted pyrroles as against dihydropyrroles, which were formed with N-sulfonyl protecting groups. This enabled a rare example wherein both dihydropyrrole and pyrrole rings are assembled in the same reaction. This strategy could be used for the synthesis of an unprecedented adjacent polyheterocyclic system having a furan-thiophene-pyrrole motif. When vinylogous carbamate is embedded in the isoindole moiety, a pyridoisoindole derivative was formed with excellent diastereoselectivity, instead of the expected pyrroloisoindole product.