Origin of the stereo- and regioselectivities in the Diels-Alder reactions of azaphospholes: a DFT investigation |
| |
Authors: | Raj K. Bansal Neelima Gupta Surendra K. Kumawat |
| |
Affiliation: | Department of Chemistry, University of Rajasthan, Jaipur 302 004, India |
| |
Abstract: | Computations of the Diels-Alder (DA) reactions of azaphosphole representative namely, thiazolo[3,2-d][1,4,2]diazaphosphole with 1,3-butadiene and isoprene at the density functional theory level reveal concerted mechanisms via asynchronous transition states. The activation energies (B3LYP/6-311++G**// B3LYP/6-311G**), 16-19 kcal mol−1, are much smaller than the value (32.57 kcal mol−1) calculated for the DA reaction of the non-phosphorus analogue, imidazo[2,1-b]thiazole with 1,3-butadiene. An electron-withdrawing group at the 3-position of the dienophile enhances both stereo- and regioselectivities, which agree nicely with the experimental values. Inclusion of solvent effect (PCM model) reveals that the stereo- and regioselectivities are not affected appreciably. The relative stabilities of the transition structures corresponding to the endo/exo stereoisomers and meta (P/Me, 1:3)/para (P/Me, 1:4) regioisomers have been rationalized on the basis of the secondary molecular orbital interactions. |
| |
Keywords: | DFT calculations Azaphospholes Diels-Alder reactions Stereoselectivity Regioselectivity NICS values |
本文献已被 ScienceDirect 等数据库收录! |
|