Abstract
The studies on the Diels-Alder reaction of masked o-benzoquinones (MOBs) 29 with acyclic dienes and furans, and the Diels-Alder reactions of 2-pyrones with 2-methoxyfuran are described. This thesis consists of three parts: the first part is concerned with the Diels-Alder reactions of MOBs with acyclic dienes. The second part deals with the Diels-Alder reaction of MOBs with furans. The last part describes the Diels-Alder reactions of 2-pyrones with 2-methoxyfuran. In the first part, two types of compounds, i.e., bicyclo[2.2.2.]octenone derivatives 52 and cis-decalins 53, were obtained in the Diels-Alder reactions of MOBs 29 and acyclic dienes. The results showed that MOBs 29 could behave as both dienes and dienophiles. The bicyclo[2.2.2.]ocetenone derivatives 52 underwent the Cope rearrangement smoothly to provide cis-decalins 53 in very high yields. Thus a novel and efficient method for stereoselective synthesis of highly functionalized cis-decalins has been developed. The investigations on the Diels-Alder reactions of MOBs 29 and furans are presented in the second part. The cycloadducts 115 or 116 were obtained as single stereoisomers in the Diels-Alder reactions of MOBs 29 with furan and its derivatives. The electron-donating groups on furan increase the rate of these reactions, whereas the electron-withdrawing groups on furan decrease the rate of these reactions. From the experiments of solvent effect, it is suggested that these reactions may be interpreted in terms of concerted cycloadditons rather than stepwise ionic reactions. According to the frontier-orbital theory and the semiempirical calculations, the HOMO of furans and the LUMO of MOBs are involved in these reactions. The results of the reactions at 0-5 ℃ monitored by 1H-NMR spectroscopy and the calculations by RHF/STO-3G and RHF/3-21G methods suggest that furans may play the role of dienophiles in these Diels-Alder reactions. It is important to note that in these processes two aromatic compounds are employed to generate highly complex and potentially useful multifunctional compounds 115 or 116 with high regio- and stereoselectivity. Especially, 2-methoxyfuran reacts with almost all MOBs to produce Diels-Alder adducts and the subsequent hydrolysis provides potentially useful multifunctional tricyclic g-lactones 112 in excellent yields in a simple one-pot process. The last part describes the Diels-Alder reactions of 2-pyrones 117 with 2-methoxyfuran. Two planar compounds are utilized to produce highly complex and potentially useful multifunctional bislactones 136 with high regio- and stereoselectivity in a simple one-pot process. From the semiempirical calculations, it is suggested that HOMO of furans and LUMO of 2-pyrones are involved in these reactions.