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

摘要

Bromination and subsequent Suzuki reactions of 2-alkylidenetetrahydrofurans,readily available by [3+2] cyclizations,afforded l'-(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.