Theoretical Study of Chemo-, Regio-, and Stereoselectivity in 1,3-Dipolar Cycloadditions of Nitrones and Nitrile Oxides to Free and Pt-Bound Bifunctional Dipolarophiles

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• 作者：Maxim L. Kuznetsov ; Alexey A. Nazarov ; Liliya V. Kozlova ; Vadim Yu. Kukushkin
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：June 8, 2007
• 年：2007
• 卷：72
• 期：12
• 页码：4475 - 4485
• 全文大小：227K
• 年卷期：v.72,no.12(June 8, 2007)
• ISSN：1520-6904

文摘

1,3-Dipolar cycloadditions of nitrones RCH=N(CH₃)O and the nitrile oxide CH₃CNO to the bifunctionalcyanoalkynes NC-CCR' and cyanoalkenes E-NCCH=CHR' (R = H, Ph; R' = H, Ph)-both freeand ligated to Pt^II and Pt^IV-were investigated by theoretical methods at B3LYP and, for some reactions,CCSD(T) and CBS-Q levels of theory. Chemo-, regio-, and stereoselectivity of the processes and factors,which affect the reactivity and selectivity, were analyzed, and verified trends are discussed in details.Coordination of dipolarophiles to Pt^II and, particularly, to Pt^IV facilitates the CN relative to the CC additionsof nitrones due to higher activation of the CN group in comparison to the CC group. The bonding of theligands to platinum also favors the meta versus ortho pathways and endo versus exo pathways thatsometimes lead to a switch of the reaction direction. Introduction of Ph groups into the reactant(s) moleculesalso leads to the promotion of the CN versus CC routes, and this effect is especially strong when bothreactants are Ph-substituted. The substituent effect is accounted for by steric repulsions imposed by thePh groups in transition states (TSs) and by the loss of a conjugation in phenylnitrone and phenylcyanoalkenemolecules upon the TS formation. Solvation inhibits the CN and meta-CC additions and, hence, generallyfavors the CC versus CN pathway, the ortho versus meta pathway, and the exo versus endo pathway. Allreactions except one proceed concertedly via a nearly synchronous mechanism for the CN and meta-CCadditions to free ligands and asynchronous mechanism for the other processes. For the reaction CH₂=N(CH₃)O + Pt^IV-1, a stepwise route is realized.