Synthesis of Benzofurans with Remote Bromide Functionality by Domino “Ring-Cleavage-Deprotection-Cyclization” Reactions of 2-Alkylidenetetrahydrofurans with Boron Tribromide

Abstract

[reaction: see text] Bromination and subsequent Suzuki reactions of 2-alkylidenetetrahydrofurans, readily available by [3+2] cyclizations, afforded 1'-(2''-methoxyphenyl)-2-alkylidenetetrahydrofurans. Treatment of the latter with boron tribromide and subsequent addition of water resulted in the chemoselective formation of functionalized benzofurans containing a remote bromide functionality. The products are formed by a new domino "ring-cleavage-deprotection-cyclization" reaction. The addition of an aqueous solution of potassium tert-butoxide, rather than water, afforded saturated analogues of calycine by a "ring-cleavage-deprotection-ring-closure-lactonization" reaction.

Synthesis of 3-methoxy-6-phenyl-6, 6a-dihydro-[1] benzopyrano- [3, 4-b] [1] benzopyran.

“…The following demethylation step is not very efficient due to the presence of the second methoxy group [25]. 4-(2-hydroxyphenylcarbonyl)-7-methoxy-1-phenylbenzopyran 5 was isolated after purification with 23% yield.…”

$$\hbox {Re}_{2}\hbox {O}_{7}$$ Re 2 O 7 -catalyzed formal [3 + 2] cycloaddition for diverse naphtho[1,2-b]furan-3-carboxamides and their biological evaluation

“…Because of their important bioactivities and pharmaceutical applications, a number of synthetic methods have been developed for the synthesis of substituted naphtho [1,2-b]furans [24][25][26][27][28]. Recently, the synthesis of naphtho [1,2-b]furans using In(OTf) 3 and Fe-Pd bimetallic nanoparticlescatalyzed reactions was reported [29,30].…”

Metal‐Free Radical 5‐exo‐dig Cyclizations of Phenol‐Linked 1,6‐Enynes for the Synthesis of Carbonylated Benzofurans

“…[2d-f] Considerable efforts have thus been directed towards the discovery of efficient methods for their synthesis. [3][4][5][6] Despite remarkable advances in benzofuran synthesis, most of the traditional methods suffer from harsh conditions, limited functional group tolerability, and/or the cost of the catalytic system. [3][4][5][6] Furthermore, the assembly of carbonylated benzofuran scaffolds remains a great challenge.…”

“…Without TEMPO, the nitration/cyclization product (2-(nitromethyl)benzofuran-3-yl)(phenyl)methanone (4 a) was isolated in 23 % yield (entry 3). Three other solvents, namely MeCN, EtOAc, and toluene, effected the reaction but were inferior to DMF (entries [4][5][6]. Screening the effect of the reaction temperature revealed that higher temperatures were favorable, and 40 8C was found to be the preferred temperature (entries 1, 7, and 8).…”