Diels–Alder reaction of 2-phosphaindolizines catalysed by organoaluminium reagent: theoretical and experimental results

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• 作者：Rajendra K. Jangid^a ; Neelima Gupta^a ; Raj K. Bansal^a ; ^{bansal56@gmail.com} ; Moritz von Hopffgarten^b ; Gernot Frenking^b ; ^{frenking@chemie.uni-marburg.de}
• 关键词：2-Phosphaindolizines ; Diels– ; Alder reaction ; Catalysis by alkylaluminium dichloride ; DFT calculations ; ¹H NMR ; ³¹P NMR ; ²⁷Al NMR
• 刊名：Tetrahedron Letters
• 出版年：2011
• 出版时间：6 April 2011
• 年：2011
• 卷：52
• 期：14
• 页码：1721-1724
• 全文大小：550 K

文摘

Theoretical calculations at the DFT (B3LYP/6-31+G^**) level of the model Diels–Alder (DA) reactions of 1-methyl-3-(methoxycarbonyl)-2-phosphaindolizine with 1,3-butadiene in the presence of methylaluminium dichloride reveal that the co-ordination of organoaluminium reagent to the carbonyl oxygen increases the activation barrier compared to that for the uncomplexed 2-phosphaindolizine. On the other hand, co-ordination of the organoaluminium reagent to the σ², bb;³ P atom lowers the activation barrier by 6 kcal mol⁻¹. 1-Methyl-2-phosphaindolizines having an electron-withdrawing group at the 3-position only undergo DA reaction with 2,3-dimethylbutadiene in the presence of the ethylaluminium dichloride catalyst in methylene chloride at a low temperature to afford [2+4] cycloadducts. The formation of an intermediate having the ethylaluminium reagent co-ordinated to σ², bb;³ P atom has been detected by ³¹P NMR. The products have been characterized by ³¹P and ¹H NMR studies.