Acid catalysis of the Claisen rearrangement. 2. Formation of the benzofurobenzopyran and benzofuro[3,2-b]benzofuran skeletons from 1,4-bis(aryloxy)-2-butynes

Abstract: An easily accessible ionic liquid, 1-methyl-3-pentylimidazolium fluoroborate, [pmIm]BF4, has been demonstrated to be an efficient catalyst as well as reaction medium for the stereoselective debromination of a variety of structurally diverse vicinal-dibromides to the corresponding (E)-alkenes in high yields under microwave irradiation. This reaction does not require any organic solvent and any metal or any conventional reducing agent, and the ionic liquid is recycled without any appreciable loss of its catalytic efficiency.

Abstract: Regioselective synthesis of dihydrofurocoumarins and dihydropyranocoumarins in excellent yields from 4-prop-2-ynyloxy coumarin via a thiol mediated radical reaction is described. Alkenyl radicals are generated from easily available terminal alkynes and thiophenol. Thiophenol catalyzed the Claisen rearrangement of the 4-prop-2-ynyloxycoumarin ethers.