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

我们最近发现，在3-和4-位上带有庞大取代基的5-芳基-2，3-二氢呋喃的单重态氧化成为一个有希望的进入热稳定的二氧杂环丁烷，其在用碱处理时容易产生CIEEL活性的二氧杂环丁烷。通过对5-芳基-4-叔丁基-3，3-二甲基-2，3-二氢呋喃的1，2-加成反应，以高立体选择性（反式：顺式= 95：5）合成了相应的双环二氧杂环丁烷。对于在3-位具有甲基和相当大的烷基如异丁基的二氢呋喃，也获得了单线态氧的立体选择性1，2-加成（立体选择性= 88：12）。二氢呋喃骨架上的进一步取代提高了单重态氧合的立体选择性。因此，将3-芳基-2-叔丁基-1-甲基-4-氧杂双环[3.3.0]辛-2-烯氧化，仅得到二氧杂环丁烷，其中从较少受阻的π-面引入二氧分子。将二氢呋喃环上取代基的空间效应控制的二氧杂环丁烷的立体选择性形成应用于由酮基甲酸合成的光学活性三环二氢呋喃，仅得到相应的二氧杂环丁烷。所有的二氧杂环丁烷在非质子有机溶剂中用碱处理时都能有效地发光。立体异构体二氧杂环丁烷的CIEEL的特征之一是立体异构体之间的化学激发效率的差异，尽管通过CIEEL过程从异构体二氧杂环丁烷产生的发光体的结构是非常相同的。

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.