A DFT Study of the [3 + 2] versus [4 + 2] Cycloaddition Reactions of 1,5,6-Trimethylpyrazinium-3-olate with Methyl Methacrylate

详细信息    查看全文

• 作者：Luis R. Domingo ; Jose A. S谩ez ; John A. Joule ; Lydia Rhyman ; Ponnadurai Ramasami
• 刊名：The Journal of Organic Chemistry
• 出版年：2013
• 出版时间：February 15, 2013
• 年：2013
• 卷：78
• 期：4
• 页码：1621-1629
• 全文大小：391K
• 年卷期：v.78,no.4(February 15, 2013)
• ISSN：1520-6904

文摘

The reaction between 1,5,6-trimethylpyrazinium-3-olate and methyl methacrylate (MMA) yielding a lactone鈥搇actam has been studied using the DFT method at the B3LYP/6-31G(d) level. It is concluded that formation of the lactone鈥搇actam is a domino process involving three consecutive reactions: (i) a 1,3-dipolar cycloaddition (13DC) reaction between the pyrazinium-3-olate and MMA yielding a [3 + 2] cycloadduct (CA); (ii) a skeletal rearrangement, which converts the [3 + 2] CA into a formal [4 + 2] CA, possessing a diazabicyclo[2.2.2]octane structure; and finally, (iii) an S_N2 reaction, promoted by halide anion, with concomitant nucleophilic attack of the created carboxylate anion on an iminium carbon with formation of the lactone ring present in the lactone鈥搇actam. Analysis of the four competitive channels associated with the 13DC reaction indicates that this cycloaddition takes place with complete endo stereoselectivity and 6 regioselectivity, yielding [3 + 2] CA. The subsequent skeletal rearrangement also takes place in an elementary step via a non-concerted mechanism. Electron localization function bonding analysis makes it possible to establish that the bicyclo[2.2.2]octane skeleton present in the lactone鈥搇actam complex structure is not attained via a Diels鈥揂lder reaction between pyrazinium-3-olate and MMA.