DFT Study on the Mechanism of Chemoselectivity in [4+2] Cycloaddition Reaction Involving Electron– Poor Dienophile with Danishefsky Diene.

The Diels –Alder reaction has to be a convenient way to assemble complex six membered cycles due to its versatility as well as its high regio- and stereoselectivities [1].The scope of this class of cycloaddition is very large and allows not only the synthesis of cyclohexene derivatives but also of a variety of heterocycles by swapping carbon atoms on the diene and/or the dienophile component with heteroatoms (O, N, S for instance; the so-called hetro- Diels-Alder reaction) [2]. The reaction between indole derivatives with Danishefskydiene leads exclusively to the Diels-Alder (DA) cycloadducts resulting from the participation of the indole 2,3-carboncarbon double bond [3].With considering the different products, we present a DFT study on the mechanism of cycloaddition reactions of indol derivatives with Danishfskydiene. Two possible mechanisms exist for this process, stepwise and concerted. The activation energies and DFT- reactivity indices was investigated for these reactions. The concerted mechanism with low activation energy is favorable path for DA and hetero-Diels-Alder(HDA) reactions. The DFT-reactivity indices can explain regioselectivity and stereoselectivity for these processes.