Syntheses and Decomposition of meso- and dl-2,3-Dimethylsuccinyl and cis- and trans-1,2-Hexahydrophthaloyl Peroxides

Abstract

The thermal decomposition of cis- and trans-1,2,-hexadyrophthaloyl peroxides (4 and 5, respectively) in dichloromethane affords cyclohexene in 27 and 32% yields, respectively. Similarly, the thermal decomposition of 4 and 5 in methanol affords cyclohexene (30%) and trace quantities of 1-methoxycyclohexane (15) and 3-methoxycyclohexene (16). No evidence for the generation of trans-cyclohexene was found. Cis and trans peroxides 4 an 5 undergo decomposition in the presence of triphenylphosphine and some aromatic hydrocarbons. Upon direct irradiation peroxides 4 and 5 afford cyclohexene in 40% yield. The thermal decomposition of meso- and dl-2,3-dimethylsuccinyl peroxides (6 and 7, respectively) affords trans- and cis-2-butenes in similar ratios (2.20). This is different from the reported braching ratio of triplet 2-butene (1.02). Meso peroxide 6 on thermal decomposition at 92° C in dichloromethan affords trans- and cis-2-butenes and threo- and erythro-2,3-dimethylproiolactones (30 and 29) in ratios of 2.2:1.0:0.3:0.1, respectively, dl Peroxide 7 on thermal decomposition at 92 °C in dichloromethane affords trans- and cis-2-butenes and threo- and erythro-2,3-dimethylpropiolactones (30 and 29) in ratios of 2.1:1.0:0.4:0.1. The intermediacy of rapidly equilibrating carboxy biradicals 32 and 33 or dicarboxy biradicals 34 and 35 that fragment to the same set of carboxy biradicals 32 and 33 is sufficient to explain the data. The thermal decomposition of meso and dl peroxides 6 and 7 in methanol affords 2-butenes as the major products and small amounts (2-4%) of methyl ethers, 2-methoxybutane (39) and 2-methoxy-3-butene (38). Irradiation of cis- and trans-2-butenes in methanol affords trace quantities of methyl ethers 38 and 39. Meso and dl peroxides 6 and 7 undergo decomposition in the presence of triphenylphosphine and aromatic hydrocarbons. The relative reactivies of induced peroxide decomposition with aromatic hydrocarbones are rubrene > perylene > diphenylanthracene. dl-2,3-Dimethylsuccinyl peroxide *7) emitted faintly visible light in the dark in the presence of rubrene. Direct irradiation of meso peroxide 6 affords trans- and cis-2-butenes and threo- and erythro-2,3-dimethylpropiolactones (30 and 29) in ratios of 2.5:1.0:0.1:0.02. Direct irradiation of dl peroxide 7 affords trans- and cis-2-butenes, threo-30, and erythro-29 in ratios of 1.9:1.0:0.3:0.03.

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