Selective photodimerisations of coumarin in crystalline inclusion compounds

Selective photodimerisations of coumarin 1 as the guest in inclusion compounds are reported. For example, irradiation of two 1:1 crystalline inclusions of 1 with (R,R)-(–)-trans-4,5-bis-(hydroxydiphenylmethyl)-2,2-dimethyl-1,3-dioxacyclopentane 8a prepared by recrystallisation of the component from toluene-hexane and ethyl acetate–hexane gave syn-head-to-head 2 and (–)-anti- head -to -head dimer 4 with 96% e.e.