Abstract
Quinones are versatile compounds because the conjugated C=O and C=C double bonds are apt to undergo synthetically useful reactions such as 1, 3-dipolar cycloaddition, Diels-Alder reaction, and Michael addition. Diazoalkanes are also useful synthones as a carbene source and a typical dipole in 1, 3-dipolar reactions. Dipolar addition of quinones with diazoalkanes occurs at these double bonds to give oxadiazolines and pyrazolines as the primary adducts. Nitrogen release of these products yields zwitterion intermediates and homoquinones. The zwitterions easily reacted with common alcohols, α, w-diols, and oligoethylene glycols to provide acyclic, cyclic, and crown ether acetals, respectively. On the other hand, homoquinones exhibited photoinduced electron transfer reactions in the presence of some amine and arene donors to afford dimeric products, xanthylium salts, amine adducts, and so on. The enedione structure of homobenzoquinones allowed the [2+2] photocycloadditions with alkenes and alkynes to construct the strained tricyclic diones.
