Concerted and Diradical Stepwise Mechanisms in the Diels-Alder
Reactions of Phosphinine and Phosphinine Sulfide: A DFT Investigation
Raj K. Bansal, Neelima Gupta, and Surendra K. Kumawat Department of Chemistry, University of Rajasthan, Jaipur 302004, India Reprint requests to Prof. Raj K. Bansal. E-mail: bansalrk43@yahoo.com Z. Naturforsch.2008,63b,321 – 330; received October 14, 2007
Computations of the concerted and diradical stepwise mechanisms of the Diels-Alder (DA) reac- tions on the>C=P– functionality of phosphinine and phosphinine sulfide with 1,3-butadiene at the density functional theory level B3LYP/6-311++G∗∗//B3LYP/6-31G∗∗ give the values of energy of concert as 10.7 and 2.6 kcal mol−1, respectively. Similarly, the DA reaction of dimethyl acetylene- dicarboxylate (DMAD) with the –CH=CH–CH=P– moiety of phosphinine or its sulfide has been investigated theoretically at the same level of theory. The results reveal that in the DA reaction of phosphinine, the role of sulfur is to oxidize phosphorus to generate a phosphinine sulfide intermedi- ate, which subsequently undergoes DA reaction with 2,3-dimethylbutadiene or DMAD by a concerted mechanism to afford the respective cycloadducts.
Key words:Diels-Alder Reaction, Phosphinine, Phosphinine Sulfide, Reaction Mechanism, DFT Calculations
