Comparison of the ΔEa of
different reactions.
For the whole reaction process, there are three elementary reactions and
three transition states. The removal of H+ and
Cl- from reactant 1a through transition state
TS1 is carried out in triethylamine solvent. The cyclization of
intermediate med2 to 3a through transition state TS3 is an
intramolecular reaction. On the other hand, the reaction between
intermediates 1a’ and 2a’ to form intermediate med1
through transition state TS2 is an intermolecular reaction that is
greatly affected by a substituent. Therefore, elementary reaction 2 was
further investigated by selecting reactants with different substituents.
Because the reaction is LUMO controlled, changing the substituent on
reactant 1a has a greater effect. The reactions (elementary
reaction 2) of 1a , 1b , 1f , 1g ,1j , 1m , 1n , and 1o with 2awere studied. Reactants 1a , 1b , 1f ,1g , 1j , and 1m contain a phenyl group with H,
CH3, OCH3, F, Cl, and Br substituents,
respectively. On the other hand, 1n is thiophene substituted
and 1o is alkyl substituted. The molecular configurations of
the reactants and products were optimized, and IRC tracing was carried
out. The calculation shows that the reaction path of dienophile1a does not change whether the substituent is an
electron-donating or electron-withdrawing group. Figures 15(a–h) shows
the IRC curves for the different substituted reactants.