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 1a–c (a: alkyl = n-C7H15; b: alkyl = CH3; c: alkyl = (CH2)7Br) 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-benzoylphenyl benzoates 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 1a–c. A cyclophane containing both benzo[1,2-b:4,5-b′]difuran and naphthalene rings was also prepared by the coupling of 1c with 2,7-dihydroxynaphthalene.