Ab initio and DFT study on the electrophilic addition of bromine to endo-tricyclo[3.2.1.02,4]oct-6-ene

Abstract

Full geometric optimization of endo-tricyclo[3.2.1.0(2,4)]oct-6-ene (endo-TCO) by ab initio and DFT methods allowed us to investigate the structure of the molecule. The double bond is endo-pyramidalized and its two faces are no longer found to be equivalent. The exo face of the double bond has regions with far more electron density (q(i,HOMO)) and more negative electrostatic potential. The endo-TCO-Br2 system was investigated at the B3LYP/6-311+G** level and the endo-TCO...Br2(exo) molecular complex was found to be relatively more stable than the endo-TCO...Br2(endo) complex. The cationic intermediates of the reaction were studied by ab initio and DFT methods. The bridged exo-bromonium cation(I) is relatively more stable than the endo-bromonium cation(II). An absolute exo-facial selectivity should be observed in the addition reaction of Br2 to endo-TCO, which is caused by steric and electronic factors. The nonclassical rearranged cation IV was found to be the most stable ion among the cationic intermediates and the ionic addition occurs via the formation of this cation. The mechanism of the addition reaction is also discussed.

Addition Reactions: Polar Addition

“…The non-classical rearranged cation was found to be the most stable ion among the cationic intermediates, implying that the ionic addition should occur via this cation. 20 Similar geometric optimization has been reported for bicyclo [3.2.2]nona-6,8-diene (BND). The double bond situated in the opposite direction to the methylene group was found to be more exo-pyramidalized than the other double bond and the electron density (qi, HOMO) of the former double bond in HOMO of the molecule higher than that of the latter double bond.…”

“…This study contributed to defining the relationship between these reactions and those catalysed by metal triflates. 36 The acid-induced cyclization of unsaturated thioacetals (19) gives anti-Markovnikov products (20), apparently involving sulfur elimination and readdition. 37…”