Theoretical study of the Diels-Alder reaction of 3-bromo-1-phenylprop-2-ynone with furan and 2-methylfuran

The Diels-Alder cycloaddition of 3-bromo-1-phenylprop-2-ynone with furan and 2-methylfuran has been studied using the molecular electron density theory through DFT calculation at the B3LYB/6-311G (d,p) level of theory. The mechanism of regioselectivity for these reactions was investigated by the potential energy surface determination for the cycloaddition process. The regiostereoselectivity was studied by exploiting the local and global reactivity descriptors defined by Fukui and Parr functions; the results showed that the diene acts as a nucleophile, by two possible approaches, namely furan and 2-methylfuran, and the dienophile behaves as an electrophile. The prediction of the possible stereo-/regioisomers for this reaction is revealed by different preferable pathways of attack. The reaction mechanism has been followed by optimizing the transition state structure using the intrinsic coordinate IRC computations and the estimated activation energies. The analysis geometries of the transition states prove that the cycloaddition is established in one step according to an asynchronous mechanism for the various rotamers.