Stereoselectivity in Diels-Alder Reactions of Diene-Substituted N-Alkoxycarbonyl-1,2-dihydropyridines

详细信息    查看全文

• 作者：Grant R. Krow ; Qiuli Huang ; Steven W. Szczepanski ; Fredrick H. Hausheer ; Patrick J. Carroll
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：April 27, 2007
• 年：2007
• 卷：72
• 期：9
• 页码：3458 - 3466
• 全文大小：168K
• 年卷期：v.72,no.9(April 27, 2007)
• ISSN：1520-6904

文摘

Diene substituent effects on the regiochemical and stereochemical outcomes of uncatalyzed Diels-Alderreactions of N-alkoxycarbonyl-1,2-dihydropyridines with both styrene and methyl vinyl ketone (MVK)were studied. Alkyl substitution on the diene in all cases examined resulted in a kinetic preference for7-endo isomers (7-phenyl 51-96% exo and 7-acetyl 54-96% exo). For both dienophiles, the higheststereoselectivities (89% endo) were observed with 5-methyl or 6-methyl substituents in the dihydropyridine. Theoretical calculations of the energies of gas phase endo and exo transition states at the RHF/3-21G(*) predict that total entropy, S_total, considerations favor endo cycloadducts for both dienophileswith DHP, while total energy considerations, E_o, favor endo cycloadducts for styrene and exocycloadducts for MVK. At this level, favored endo-phenyl isomers are correctly predicted for styrenereactions, but the calculation of 7-acetyl exo or endo isomer dominance is diene-substituent-dependentfor MVK reactions. The preference for endo addition of MVK to the parent, 5-methyl, and 6-methyl-DHPs was successfully predicted by calculations at the B3LYP/6-31G* theory level.