Gonzalez-Rosende, ME,Sepulveda-Arques, J,Zaballos-Garcia, E,Domingo, LR,Zaragoza, RJ,Jennings, WB,Lawrence, SE,O'Leary, D;

1999

January

Rna-A Publication of The Rna Society

Domino reaction between 2-acylfurans and diethyl azodicarboxylate: a combined experimental, theoretical, X-ray and dynamic NMR study

Validated

()

DIELS-ALDER REACTION STEREOCHEMISTRY FURANS

73

79

Treatment of 2-acetylfuran 6a with diethyl azodicarboxylate gave the cycloadduct 7,6,7-diethoxycarbonyl-6,7-diazas-oxabicyclo[3.2.1]oct3-en-2-one, whereas 5-methyl-2-formylfuran 6b reacted giving a simple hydrazide product derived from radical reaction on the formyl group. The structure of the bicyclic compound 7, established by NMR measurements, was confirmed by an X-ray crystallographic analysis. Variable temperature H-1 NMR and C-13 NMR studies of 7 indicate that this compound undergoes two distinct dynamic conformational changes with Delta G double dagger 10.2 and 13.1 kcal mol(-1) respectively. The reaction mechanism associated with the domino reaction between furfural I and dimethyl azodicarboxylate 9 to give the cycloadduct 10 has been theoretically characterized using ab initio methods at the RHF/6-31G* level. The reaction pathway can be described as a three-step process. The first step corresponds with a [4 + 2] cycloaddition between 1 and 9, while the two subsequent steps are associated with a structural isomerization of the initial formyl cycloadduct to a more stable final adduct.