DESIGN AND STEREOSELECTIVE SYNTHESIS OF CIEEL-ACTIVE DIOXETANES AND THEIR CHEMILUMINESCENCE

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Singlet oxygenation of 5-aryl-2,3-dihydrofurans bearing a bulky substituent at the 3- and 4-position has recently been found by us to become a promising entry to thermally stable dioxetanes which produce easily CIEEL-active dioxetanes on treatment with base. This fact prompted us to investigate stereoselective synthesis of CIEEL-active dioxetanes and to realize noble optically active one.1,2-Addition of singlet oxygen to 5-aryl-4-t-butyl-3,3-dimethyl-2,3-dihydrofurans bearing a bulky substituent (R) such as t-butyl and phenyl proceeded to give the corresponding bicyclic dioxetanes with high stereoselectivity (anti-form : syn-form = 95 : 5). Stereoselective 1,2-addition of singlet oxygen was also attained for dihydrofurans having a methyl and rather bulky alkyl such as isobutyl at the 3-position (stereoselctivity = 88 : 12). Further substitution on the dihydrofuran skeleton improved the stereoselectivity of singlet oxygenation. Thus, 3-aryl-2-t-butyl-1-methyl-4-oxabicyclo[3.3.0]oct-2-ene was oxygenated to give exclusively a dioxetane in which a dioxygen molecule is introduced from the less hindered π-face. The stereoselective dioxetane formation controlled by steric effect of substituents on the dihydrofuran ring was applied to an optically active tricyclic dihydrofuran synthesized from ketopinic acid to afford the corresponding dioxetane exclusively. All dioxetanes sythesized here emitted light effectively on treatment with base in aprotic organic solvent. One of characteristic features of the CIEEL for stereoisomeric dioxetanes was the difference in chemiexcitation efficiency between stereoisomers though the structure of emitter produced from the isomeric dioxetanes through CIEEL process was the very same.