Benzofurans, Friedel-Crafts cyclization

Reaction of the potassium salt of salicylaldehyde with chlo-roacetone affords first the corresponding phenolic ether aldol cyclization of the aldehyde with the ketonic side chain affords the benzofuran (1). Reduction of the carbonyl group by means of the Wolf-Kischner reaction affords 2-ethyl-benzofuran. Friedel-Crafts acylation with anisoyl chloride proceeds on the remaining unsubstituted position on the furan ring (2). The methyl ether is then cleaved by means of pyridine hydrochloride (3). lodina-tion of the phenol is accomplished by means of an alkaline solution of iodine and potassium iodide. There is thus obtained benziodarone (4)... 

An intramolecular cychzation of an aryl ether to the carbonyl of a pendant aryl ketone, on clay with microwave irradiation, led to a benzofuran via Friedel-Crafts cyclization and ehmination of water. 

A recent halogen-free benzofuran that shares many structural features with its predecessor shows activity in controlling arrythmias. The synthesis starts with an unusual scheme for building the furan ring. Reaction of the benzyl bromide (2-1) with triphenylphosphine leads to phosphonium salt (2-2). Treatment of the salt with valeryl chloride in the presence of pyridine results in acylation on the now highly activated benzylic carbon (2-3). That product cyclizes to the benzofuran (2-4) on heating with expulsion of triphenylphosphine. Friedel-Crafts acylation of (2-4) with anisoyl chloride in the presence of stannic chloride proceeds on the... 

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