Application of Vilsmeier Reagents in Cyclization in Recent Years

Abstract

The Vilsmeier-Hack reaction has historically been a topic of great interest to organic chemists, and it continues to attract considerable attention. The Vilsmeier-Hack reaction provides a facile entry into large numbers of aromatic and heteroaromatic systems. Vilsmeier reagents generated from amides and halides have been found to be very important in organic synthesis. Acylation, chlorination, chloroformylation, aromatization, rearrangement, dehydration and cyclization are the most reactions of Vilsmeier reagents. The application of Vilsmeier reagents in cyclization is introduced.

Chemistry of Ketene N,S-Acetals: An Overview

“…Under identical conditions, 118b was produced from 62h , and 118b can be further converted to the desired 3,4-diarylpyrrole-2-carboxylate by demethylthiolation with Raney Ni. For the cyclization reaction, a tandem aminomethylenation–cyclization sequence is thought to be involved, on the basis of the performance of the Vilsmeier reagent. , …”

“…The experimental results showed that (1) reactions of 36 without activating group on aniline are sluggish toward Vilsmeier reagent to furnish the desired quinolines (products 162a and 162h/h′ ); (2) 36h , having the 3-fluoroanilino group, afforded a regioisomeric mixture of 162h and 162h′ ; (3) reaction of 36b′ afforded the angularly fused 162i instead of the corresponding linearly fused 162i′ ; and (4) 36j gave 165 as the only identifiable product in 50% yield . On the basis of these results and related reports on Vilsmeier reagents, ,,,− related mechanisms are proposed as described, and the formylation or acylation at the acceptor end of aroyl ketene N , S -acetals by POCl 3 /DMF or POCl 3 /DMA (where DMA = N , N -dimethylacetamide) should be the key step for construction of 162 (Table ).…”

“…For the cyclization reaction, a tandem aminomethylenation−cyclization sequence is thought to be involved, on the basis of the performance of the Vilsmeier reagent. 149,150 Significantly, intramolecular cyclization of 62g can be activated by formation of the iminium intermediate 120, where the C atom is more electrophilic, allowing for a 1,4conjugate addition to the unsaturated imidate thiolester. 3,4-Diarylpyrrole-2-carboxylate analogues are key intermediates in the synthesis of marine pyrrole alkaloids, such as lukianol A and lamellarin O (Scheme 28).…”