Current Catalysis

Shaobin Wang  
Curtin University
Perth, WA 6845 U1987
Australia

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Catalytic Effect of Organoaluminium Chloride Reagents on the Dienophilic Reactivity of Indolizine and 2-Phosphaindolizine towards [2+4] Cycloaddition: A DFT Investigation

Author(s): Neelima Gupta, Rajendra K. Jangid, Raj K. Bansal, Moritz von Hopffgarten.

Abstract:

The catalytic effect of the aluminium chloride reagents R1AlCl2 (R1 = Cl, Me, Et) on the dienophilic reactivity of the >C=C< functionality of indolizine and >C=P- functionality of 2-phosphaindolizine in their Diels-Alder (DA) reaction with 1,3-butadiene has been investigated theoretically at the DFT (B3LYP/6-31+G**) level. The activation barriers of the DA reactions of the uncomplexed dienophiles with 1,3-butadiene are quite high. Co-ordination of the aluminium reagent to the carbonyl group of indolizine or 2-phosphaindolizine raises the activation barriers further. On the other hand, co-ordination of the aluminium catalyst to the σ2, λ3-P atom of 2-phosphaindolizine lowers the activation barrier making the DA reaction possible. Electronic structure calculations of indolizine, 2-phosphaindolizine and their complexes to the aluminium catalyst indicate, that this behavior can be explained by a combination of energetic and stereoelectronic influences of the catalyst on the lowest unoccupied molecular orbital (LUMO) of the dienophiles. Co-ordination of the aluminium catalyst to the dienophile lowers the orbital energy of the LUMO in any case making it energetically more feasible for the normal electron demand DA-reactions. However, O co-ordination polarizes the spatial distribution of the LUMO away from the dienophilic center while P co-ordination increases the orbital contribution of the >C=P fragment to the LUMO.

Keywords: Density functional theory calculation, Diels-Alder reaction, indolizine, 2-phosphaindolizine, organoaluminium catalyst, LUMO, DMAD, cycloadducts, natural bond orbital, exothermicities, dienophile, normal electron demand, HOMO, SCRF-PCM, Polarisable Continuum Model

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Article Details

VOLUME: 1
ISSUE: 2
Year: 2012
Page: [93 - 99]
Pages: 7
DOI: 10.2174/2211544711201020093
Price: $58