Synthesis of benzo[1,2-b:4,5-b′]difuran derivatives utilizing concomitant photocyclization and photo-Fries rearrangement reactions

A synthetic route for 2,6-dialkyl-3,7-diphenylbenzo[1,2-b:4,5-b']difurans la-c (a: alkyl = n-C7H15; b: alkyl = CH3; c: alkyl -(CH2)(7)Br) from p-dimethoxybenzene utilizing photocyclization and photo-Fries rearrangement reactions is described. Dimethoxybenzene was reacted with benzoyl chloride to obtain 3-benzoyl-4-hydroxyphenyl benzoate 5, and the reaction of 5 with alkyl halides gave 4-alkoxy-3-benzoylphenylbenzoates 6a-c. Photoirradiation of 6a-c followed by dehydration afforded 2-alkyl-6-benzoyl-5-hydroxy-3-phenylbenzofurans 7a-c via concomitant photocyclization and photo-Fries rearrangement. Etherification of 7a-c with alkyl halides gave 5-alkoxy-2-alkyl-6-benzoyl-3-phenylbenzofurans 11a-c, and photocyclization/dehydration reaction of 11a-c provided 2,6-dialkyl-3,7-diphenylbenzo[1,2-b:4,5-b']difuran compounds la-c. A cyclophane containing both benzo[l,2-b:4,5-b']difuran and naphthalene rings was also prepared by the coupling of le with 2,7-dihydroxynaphthalene. (C) 2004 Elsevier B.V. All rights reserved.