A concise route to functionalized benzofurans directly from gem-dibromoalkenes and phenols

Abstract

A tandem strategy for the construction of benzofuran motifs has been developed directly from gemdibromoalkenes and phenols under palladium-catalyzed conditions. This flexible and novel methodology provides direct access to 2-aryl and 2-styryl benzofurans in good to high yields. This strategy is also valuable in the synthesis of benzodifurans.Scheme 1 One-pot strategy.

Palladium‐Catalyzed Allenylation/6π‐Electrocyclization and 1,3‐Hydrogen Migration: an Access to Naphtho[1,2‐b]furans

“…3a was obtained in a relatively lower yield (Table 1, entries 3-5). did not produce better results (Table 1, entries [14][15][16]). Other bases such as K 2 CO 3 , NEt 3 and DBU did not give better results than those obtained with Cs 2 CO 3 ( 1, entry 12).…”

“…Changing the amount of Cs 2 CO 3 to 1.0, 1.5, 2.5 equiv. did not produce better results (Table 1, entries [14][15][16]). An open atmosphere resulted in a slightly lower yield (Table 1, entry 17).…”

“…Prefunctionalized naphthol, such as 2-allyl naphthol, [10a-10c] 2-alkenylnaphthol, [11a-11c] 2-alkynylnaphthol [11d] are also often used to construct naphtha[b]furans. In recent years, some more straightforward methods were reported for the synthesis of naphtha[b]furan skeleton from simple naphthol and other active reagents, including nitroalkenes, [12a,12b] propargylic alcohols, [13] gem-dibomoalkenes, [14] propargylic carbonates [15] and alkynes [16a-16d] etc. Most of above transformations involve the use of naphthol and its derivatives and lack generality.…”

Metal-Free Oxidative Annulation of 2-Naphthols with Terminal Alkynes Affording 2-Arylnaphtho[2,1-b]furans

“…Furan derivatives, especially for arene ring-fused furans, are an important class of structural motifs in a large number of natural products, synthetic drugs, and biologically active compounds, as well as organic materials . These compounds are commonly prepared by transition-metal-catalyzed annulation of alkynyl-substituted phenols or tandem reaction of o -halophenols with terminal alkynes via cross-coupling and subsequent annulation. , Recently, direct oxidative functionalization of phenols with alkynes has attracted significant interest because of the employment of simple and accessible phenols for straightforward synthesis of these compounds, and some notable advances have been made (Scheme ). Sahoo and co-workers explored a Pd-catalyzed oxidative annulation of phenols with internal alkynes to give 2,3-diarylbenzo­[ b ]­furans.…”