Chemistry of O ‐Benzoquinones and Masked O ‐Benzoquinones I. Diels‐Alder Reactions of O ‐Benzoquinones with Dimethyl Acetylenedicarboxylate and Phenylacetylene

Diels‐Alder reactions of six o ‐benzoquinones with dimethyl acetylenedicarboxylate has been examined. The yields of adducts vary with the natures of the o ‐benzoquinones, 3,4‐Di‐ n ‐propyl‐(1c), 3,6‐di‐ n ‐propyl (1d). 3. 4‐diallyl‐(1e) and 3, 6‐diallyl‐ o ‐benzoquinone (1f) are found to give bicyclic a‐diketones exclusively without the formation of 1,4‐dioxine derivatives, the yields ranging from 20 to 70%. In the case of 4, 5‐dimethoxy‐ o ‐benzoquinone, dimethyl 4, 5‐dimethoxyphthalate is produced in 42% yield, presumably derived from the decomposition of the corresponding initially formed α‐diketone. 3, 6‐Di‐ n ‐propyl‐4, 5‐dimethoxy‐ o ‐benzoquinone deteriorates without addition to dimethyl acetylenedicarboxylate upon heating. The additions of o ‐benzoquinones 1c , 1d and 1f to phenylacetylene are also studied. The yields of adducts, α‐diketones, range from 23% to 82%.