Trans-Stilbene, photocycloaddition with

Addition to six-membered oxygen heterocycles is also common. The photocycloaddition of 5,7-dimethoxycoumarin to tetramethylethylene has been described, and 4-hydroxycoumarin (326) undergoes facile addition to cyclohexene on direct irradiation to give the cyclobutane (327) analogous additions to a variety of other alkenes have been reported, and the cycloaddition of 4-methoxycoumarin to 2-methylpropene has been employed in a synthesis of l,2-dihydrocyclobuta[c]coumarin. Photoaddition of the 1,2-bisenol lactone (328) to trans-stilbene yields propellane (329), and [ 2 -F, 2] cycloaddition is observed along with other competing photoreactions on irradiation of chromone in the presence of alkenes. ... 

The first successful example of an enantioselective and intermolecular 12 -I- 21 photocycloaddition involved the reaction of chiral fumarates 165 with trans-stilbene. After removal of the chiral auxiliaries, the ee of the dimethyl-5-truxinate (166) and /i-truxinate (167) produced depends strongly on the nature of the chiral appendages of the starting maleates (Scheme 27) [106]. 

---