The dimerisation of 2-methoxycarbonylbuta-1,3-diene: the importance of paralocalisation energy in assessing diene reactivity

Abstract

The dimerisation and competitive cycloaddition of 2-methoxycarbonylbuta-1,3-diene with electron-rich dienes has been investigated. Experimental results provide evidence that the enthalpy of the -system significantly influences the energy of the transition state of cycloadditions of this type. This has been corroborated by ab initio calculations. We propose an early reorganisation of the -electrons in such cycloadditions to explain the influence stated above.

Why do Electron‐Deficient Dienes React Rapidly in Diels−Alder Reactions with Electron‐Deficient Ethylenes? A Density Functional Theory Analysis

“…This twist, together with C2ϪC7 BO value (0.96), suggests the non-conjugation of the COOMe group with C1ϪC2 double-bond, and explains the participation of the C1ϪC2 π-bond in a nucleophilic attack. A similar participation would be expected for the C3ϪC4 π-bond of 2-azadienes [11] and 2-carbomethoxy-1,3-butadiene [12] towards strong electrophiles. Note that the COOMe group present at the C3 position is now planar to the diene system, but it is not in a conjugated position relative to the C1ϪC2 π-bond.…”

“…[11] Why does 2-carbomethoxy-1,3-butadiene dimerize much faster than it reacts with ER reagents? [12] (Note that these cases are similar to the DA reaction between the ED diene 1 and the ED ethylene 5a, which has a rate of the same order of magnitude as that for the reaction between 1 and the ER ethylene 2a.) [9] In these cases, the choice of which pair of frontier orbitals to take is sometimes difficult because of the closer HOMOϪ LUMO gap energies for both ED reagents.…”

Unravelling the Synthesis and Chemistry of Stable, Acyclic, and Double‐Deficient 1,3‐Butadienes: An endo‐Selective Diels–Alder Route to Hedgehog Pathway Inhibitors

“…We assumed that a single bond rotation in dienes 13 under the reaction conditions may offer the s ‐cis conformation and facilitate the Diels–Alder (DA) reaction. We chose to first explore N ‐methylmaleimide (NMM) as an electron‐poor dienophile,, in the DA reaction with dienes 13 . To this end, when the E , E ‐ or Z , E ‐diene 13 a or 13 ′ a , respectively, were heated with NMM in toluene under MW irradiation (300 W, 200 °C) for 4 h, a complex and unresolvable product mixture was formed.…”

Synthesis of 4-Aminocyclohex-1-enecarboxylates from Danishefsky's Diene

“…3 However, the usefulness of the resulting b-methoxy silyl enol ether adduct 1 in the synthesis of other compounds has been limited. [4][5][6] In his first studies, Danishefsky transformed 1 into an ethylene acetal in situ by direct treatment with ethylene glycol. While conversion of 1 into a mixture of enones 2 and 3 has been reported by Jung 5 and incidentally by Spino.…”

“…While conversion of 1 into a mixture of enones 2 and 3 has been reported by Jung 5 and incidentally by Spino. 6 The preparation of enones 2 and 3 has also been reported as the result of transformations of several adducts obtained by Diels-Alder reactions between dienes other than Danishefsky's and methyl acrylate, 7 but with poor yields or even as secondary products. 8 Additionally, it is noteworthy that the reaction of 2-trimethylsilyloxy-1,3-butadiene and methyl propiolate is not regioselective, giving compounds of type 3 in its ethylene acetal form in only 60% overall yield.…”