Base-Induced Chemiluminescent Decomposition of Bicyclic Dioxetanes Bearing a (Benzothiazol-2-yl)-3-hydroxyphenyl Group: A Radiationless Pathway Leading to Marked Decline of Chemiluminescence Efficiency

Charge-transfer-induced decomposition (CTID) of bicyclic
dioxetanes 1b–d bearing a 3-hydroxylphenyl
moiety
substituted with a benzothiazol-2-yl group at the 2-, 6-, or 5-position
was investigated, and their chemiluminescence properties were compared
to each other, based on those for a 4-benzothiazolyl analogue 1a. Dioxetanes 1c and 1d underwent
CTID to give the corresponding oxido anions of keto esters 8c or 8d in the singlet excited state with high efficiencies
similarly to the case of 1a. On the other hand, 1b showed chemiluminescence with quite low efficiency, though
it gave exclusively keto ester 2b. The marked decline
of chemiluminescence efficiency for 1b was attributed
to 1b mainly being decomposed to 8b through
a radiationless pathway, in which intramolecular nucleophilic attack
of nitrogen in the benzothiazolyl group to dioxetane O–O took
place to give cyclic intermediate cis-11.