Correlations between Carbon-13 Nuclear Magnetic Resonance Chemical Shifts and Reactivities of Siloxybutadienes and Siloxyazabutadienes in the Diels-Alder Reaction with Dimethyl Acetylenedicar-boxylate

In the reaction of silylated butadiene derivatives (1) with dimethyl acetylenedicarboxylate (DMAD), it is proposed that the reactivities of the dienes can be predicted from the carbon-13 nuclear magnetic resonance chemical shifts of the terminal methylene carbons (£¹³C-4) of the dienes based on the following linear relationships, a) total electron densities against d¹³C-4; b) In k against l/[£_LuMO(DMAD)-£HOMo<die„e)]; c) In k against <5¹³C-4. The total electron densities and energy levels of highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of the dienes were calculated by the modified neglect of diatomic overlap (MNDO) method.