Dihydrofurans, photoadditions

The stereochemical outcome of this photoaddition can be rationalised by the cyclopentenone adding on to the less hindered exo-face of the bicyclic dihydrofuran 7, as shown in Figure 6.1. 

The photoaddition of benzophenone to the vinyl sulphides (54) affords a mixture of the oxetanes (55) in yields ranging from 12 - 79X dependent on the alkene used. - Photoaddition of aldehydes to 2,3-dihydrofurans has been studied. The addition affords oxetanes of the type shown by (56) where addition of benzaldehyde affords two isomers. Addition to the furan derivative (57) was also studied. In this instance the addit ion of aldehydes afforded two types of oxetane illustrated by (58) and (59). ... 

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