Development of New Organic Reactions by Use of Electron Acceptor Quinones

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[2+2] photocycloaddition: Irradiation of various meto- and para-substituted homobenzoquinones with ethyl vinyl ethers gave the [2+2] photoadducts regio- and endo-selectively. The adducts have an antiform built by the addition of ethyl vinyl ethers from the less hindered side of homobenzoquinones. All of the CH_3, Cl, Br, and CH_3O substituents at the reacting C = C double bond afforded head-to-head addition predominantly. In the case of CH_3, Cl, and Br, the ethoxy group was -oriented in the endoposition, while the CH_3O substituent led to a 1/5 mixture with the exo-isomer. It was also found that the Br-substituted [2+2] adducts undergo a facile skeletal rearrangement, being converted into dihydro-obenzoquinone methide for para-substituent and dihydro-o-benzofuran derivatives for meta-substitution, probably under the influence of the in sit generated HBr.Diels-Alder reactions of quinocrown ethers: 15-21-membered auinocrown ethers 1a-c and 18-membered quinobenzocrown ether 1d with cyclo … More pentadiene were catalyzed by the addition of alkali, alkaline earth metal and ammonium perchlorates, and scandium trifluoromethane-sulfonate. The alkali metal ions brought about a fairly selective rate-acceleration for each crown ether due to the size-fitted ion-in-the-hole complexation. However, such a hole-size-selectivity was not observed for the reactions catalyzed by divalent alkalie earth (Mg^<2+> to Ba^<2+>) and trivalent Sc^<3+> ions. The wrapping complexation played a significant role in rate-acceleration in such a way that the smallest Mg^<2+> caused 160 times rate-enhancement for the most flexible 1c and the Sc^<3+> performed maximal 3700 times rate-increment for the 18-membered quinobenzocrown 1d. These effects of cation recognition were rationalized by the reduction of LUMO energy that is favored by the orbital interaction with the HOMO of cyclopentadiene. The magnitude of rate-enhancement was expained in terms of the cation binding affinity and coordination geometry of quinocrown ethers as well as the valence of cations. Less