Synthesis of novel cyclophanes containing both benzo[1,2-b:5,4-b′]difuran and naphthalene rings
Facile routes for the synthesis of novel cyclophanes 1a, b containing both benzo[1,2-b:5,4-b′]difuran and naphthalene rings have been developed. Irradiation of 1,5-dibenzoyl-2,4-dialkoxybenzene derivatives 3a, b with a 350 nm mercury lamp followed by dehydration afforded benzo[1,2-b:5,4-b′]difuran ring systems 5a, b. The cyclophanes 1a, b were prepared either from the ether-forming reaction between the preformed benzodifuran ring derivatives 5a, b and 2,7-dihydroxynaphthalene, or from the photocyclization–dehydration reaction of the macrocycles 6a, b prepared by reacting 1,5-dibenzoyl-2,4-bis(ω-bromoalkoxy)benzene with 2,7-dihydroxynaphthalene. The cyclophanes 2a, b containing two benzo[1,2-b:5,4-b′]difuran and two naphthalene moieties were obtained as minor products.