Table 3.
Endo (n) and Exo (x) TS Geometries and Energetics for a Range of Silyloxydienes and Other Model Dienes with Dienophile Complex A2 or Dienophile 3, with an Emphasis on Twist-Mode Asynchronicity.
| Entry | Diene | TS geometry | ΔG‡298a | ΔE0‡b | θc | Me(H)–Me dihedral angle | |
|---|---|---|---|---|---|---|---|
| endo | exo | ||||||
| 1 |  |
 |
 |
28.3(n) 24.3(x) | −0.1 (−11.4) (n) −3.0 (−13.5) (x) | −33° (n) +22° (x) | 24°(n) 72°(x) |
| 2 |  |
 |
 |
24.1(n) 24.0(x) | −2.0 (−13.1) (n) −2.1 (−11.4) (x) | −5°(n) +10°(x) | 53°(n) 58°(x) |
| 3 |  |
 |
 |
25.9(n) 23.6(x) | 0.4 (−11.0) (n) −1.7 (−11.4) (x) | −13°(n) +23°(x) | 44°(n) 73°(x) |
| 4d |  |
 |
 |
42.7(n) 40.1 (x) | 21.0 (4.5) (n) 20.2 (5.6) (x) | +9°(n) +23°(x) | 67°(n) 75°(x) |
| 5 |  |
 |
 |
28.9(n) 29.6(x) | 6.9 (−3.8) (n) 7.3 (−2.1) (x) | −3°(n) +12°(x) | 57°(n) 58°(x) |
| 6 |  |
 |
 |
34.7(n) 33.3(x) | 10.6 (−4.2) (n) 9.1 (−4.5) (x) | +12°(n) +16°(x) | 71°(n) 64°(x) |
a
Gas phase Gibbs energy at B3LYP/6−31G(d) level, corrected for solvent effects by PCM single-points at HF/6−31+G(d,p) on B3LYP/6−31G(d) vacuum optimized geometries.
b
Gas phase uncorrected electronic energy at B3LYP/6−31G(d)//B3LYP/6−31G(d) level. The corresponding energy at MP2/6−31+G(d)//B3LYP/6−31G(d) level in parentheses.
c
Twist-asynchronicity parameter. See Figure 6b for definition.
d
In the absence of Me2AlCl (i.e. with dienophile 3).