There are two possible explanations for the high yields in the intramo
lecular [2 + 2] photocycloaddition of compounds 3a-d in which two styr
ene moieties are bridged by an oligooxyethylene linkage: one is the el
ectronic effects of phenoxy oxygen atoms at the para-position of the v
inyl group and the other is the steric effects due to the flexibility
of oligooxyethylene linkages. In order to clarify the contributions of
the two effects, a study was made of the photoreaction of similar com
pounds in which oxygen atoms are present only at the ends of the chain
, and therefore only the electronic effects are involved. In these com
pounds, the quantum yields of the photocycloaddition were found to be
low. Hence the high yields in the photocycloaddition of 3a-d are concl
uded to be ascribable to the flexibility of oligooxyethylene linkages.
(C) 1998 John Wiley & Sons, Ltd.