Phthaloyl peroxide, loss

The synthesis of fused oxetane derivatives via the Paterno-Bchi cycloaddition of carbonyls and alkenes is discussed in detail in a representative example is shown in Scheme 7 <2001CEJ4512>. See also Sections 3.3.1.8.3 and 3.4.1.10.5 for the preparation of fused oxetanes and azetdines by [2 + 2] cycloaddition reactions. Benzox-etan-2-one 10 has been prepared in an argon matrix by C02 loss from phthaloyl peroxide <1973JA4061>. 

Carboxylate esters readily undergo photodecomposition with loss of carbon dioxide. Not surprisingly, lactones and related oxygen heterocycles undergo related transformations. A wide variety of lactones behave in this fashion" for example, the cyclic dilactone (505) is converted on irradiation to the [2.2]paracyclophane (506). Of particular interest is the use of the jS-lactone (507) as a precursor of matrix-isolated cyclobutadiene (508)." Phthaloyl peroxide (509) has similarly been employed as a precursor of benzyne (510). A careful examination in an argon matrix at 8 K has revealed that the / -lactone (511) and the keto ketene (512) are intermediates... 

Phthaloyl peroxide, in contrast to diphenoyl peroxide cannot decarboxylate readily to give a stable lactone. The corresponding lactone (25) is unreasonably strained. The as yet unknown phenanthrene dicarboxylic acid and naphthalic peroxides (26) and (27) could form stable lactone radical anions by loss of CO2 on acceptance of an electron from the activator. 

The reactions of these peroxides are clearly different from those of diphenoyl peroxide. The mechanism is likely to be complex since oxidative transformation of the added fluorescer occurs to a large extent. The main differences are that peroxides related to phthaloyl peroxide show little loss of CO2 (about 17%) whereas the yield in the case of diphenoyl peroxide is about 80%. Quenching by oxygen is observed, but in the CIEEL pathway quenchers such as H2O, oxygen and tetramethyl ethylene have little influence. 

---