Stereoselective synthesis of meta- and three-bridged cyclophanes with intramolecular [2 + 2] photocycloaddition by using the steric effect of methoxyl group
Dimethoxy[n.2]metacyclophanes 9 (n=2, 3, 4, 5, and 6) and 10 were stereoselectively obtained in 61 – 87% yields by means of[2+2] photocycloaddition. Their conformations, when n=3-6, are exclusive of syn, while the dimethoxy[2.2]metacyclophane exists as a mixture of syn and anti isomers with the ratio of 4:3. After their Birch reduction, [n.4]metacyclophanes 11 (n=2 - 6) were successfully obtained in