The Preparation of Photoresponsive Cyclobutanocrown Ethers by Means of Intramolecular Photocycloaddition

Article abstract of DOI:10.1246/bcsj.61.2459

The reaction of o-bis(3-hydroxy-1-oxapropyl)benzene (7b) with 3.3'-(trimethylenedi-4,1-phenylene)bis<2-propenoyl chloride>gave 8,9-benzo-4,7,10,13-tetraoxa<16.3>paracyclopha-1,8,15-triene-3,14-dione (8b) in a 6,5percent yield, together with its dimer in a 12.3percent yield.Also, 5,6-benzo-4,7-dioxa<10.3>paracyclopha-1,5,9-triene-3,8-dione (8a) and 11,12-benzo-4,7,10,13,16,19-hexaoxa<22.3>paracyclopha-1,11,21-triene-3,20-dione (8c)were obtained by the same method in 7.0 and 8.0percent yields, together with their respective dimers (9a: 6.0percent, 9c: 20.8percent).X-Ray analysis of 8b revealed the two double bonds to be trans and the distances between the two olefinic carbon atoms (C17-C35) and (C18-C34) to be 5.341(11) and 5.906(9) Angstroem respectively.These distances are too long for intramolecular <2+2>photocycloaddition to occur in the crystalline state.However, the irradiation of the solutions of the crown ethers 8a and 8b in acetonitrile by Pyrex-filtered UV light (>300 nm) gave two intramolecular <2+2>photocycloadducts, cyclobutanocrown ethers 10a and 10b, in 95.7 and 91.8percent yields respectively.Subsequently, 10a and 10b were transformed to 8a and 8b in 37 and 29percent yields respectively upon irradiation with 220 nm UV light.The structures of 10a and 10b were confirmed to be the β-form.