Conformational analysis. CV. Syn-diaxial methyl carboethoxy interaction

Multicomponent, Enantioselective Michael–Michael-Aldol-β-Lactonizations Delivering Complex β-Lactones

“…TLC (EtOAc:hexanes, 1:9 v/v): R f = 0.50; 1 H NMR (300 MHz, CDCl 3 ): δ 6.46 (s, 2H), 4.24 (q, J = 7.2 Hz, 4H), 1.28 (t, J = 7.1 Hz, 6H); 13 C NMR (75 MHz, CDCl 3 ): δ 164.0, 135.2, 134.0, 61.5, 14.1. Other spectral data matched those previously reported …”

Characteristics of the Two Frontier Orbital Interactions in the Diels−Alder Cycloaddition

“…With respect to both dienes, maleic anhydride (MA; 10), 1,1-carbethoxyethene (CEE; 11), 19 and dimethyl fumarate (DMFu; 12) were of similar reactivities (Tables 1 and 2, entries 1, 2, and 3). Maleic anhydride benefits from a diminished steric encumbrance and a lower LUMO (Figure 5).…”

“…We can thus conclude that the electronics is the controlling element in the reactivity of these dienophiles and not steric effects. Steric effects may, however, lower the reactivity of 20 with respect to DEE (19).…”

Synthesis of a Constitutional Isomer of Nerol by Consecutive Ireland–Claisen and Cope Rearrangements

“…shaped E and F of which are sterically very demanding. For the chair-like conformations C and D, we can estimate the total destabilization energy E D from the experimentally known values for the 1,3-syn-diaxial interactions, assuming that Ϫ∆G°M e/COOH ഠ Ϫ∆G°M e/COOEt ϭ 3.2 kcal·mol Ϫ1 , [25] because Ϫ∆G°C OOH/H ഠ Ϫ∆G°C OOEt/H ഠ 1.2 kcal·mol Ϫ1 . [26] With Ϫ∆G°M e/H ϭ 1.6 kcal·mol Ϫ1 , [26] and Ϫ∆G°M e/Me ϭ 3.7 kcal·mol Ϫ1 , [27] we obtain: Figure 1.…”