Comparison of an intramolecular Michael-type addition with its intermolecular counterpart: an abinitio theoretical study

Abstract

C. I. F. GREIN. Can. J. Chem. 67, 2173 (1989). Ab initio theoretical calculations were carried out on the intramolecular addition of 3-ketopent-4-en-I-olate 1 to form 1-oxacyclohex-3-en-4-olate 2 (reaction I; Scheme 1) and the corresponding intermolecular Michael addition of methanolate to butenone forming 4-methoxybut-2-en-2-olate 4 (reaction LI; Scheme 1). The calculations were carried out at the RHF level using an augmented 4-3 1G basis set; single point energies were then taken using the 6-31 +G* basis set. The overall energy change of the reaction in going from reactants to products is very similar for both reactions, with products being about 8.3 kcallmol more stable than reactants; the major difference energetically between the two reactions is at the level of the transition state: the transition state energy for reaction I (intramolecular) is 6 kcallmol higher than that for reaction I1 (intermolecular). The transition state geometry of reaction I1 conforms quite closely to the stereoelectronic requirements for a Michael addition, but that of reaction I is very distorted, reflecting significant compromises in the stereoelectronic requirements.

Novel Synthesis of Substituted 2-Trifluoromethyl and 2-Perfluoroalkyl N-Arylpyridinium Compounds—Mechanistic Insights

“…Indeed, the literature [71] states that electronic and steric effects of substituents have very pronounced influence on both intermolecular Michaël 1,4-additions or Diels-Alder cycloadditions. Many studies show that stereoelectronic requirements for certain intermolecular reaction and the resulting increase in the potential energy for the corresponding transition states, could be so high that intramolecular cyclisation could take place instead [71]. In both cases anyway (either cycloaddition or cyclization), the subsequent elimination of two aniline molecules, may ensure irreversibility, again because of entropic effects.…”

Designing a Transition State Analogue for the Disfavored Intramolecular Michael Addition of 2-(2-Hydroxyethyl)acrylate Esters

“…The values of the attack angles are 104.8° and 114.9°, respectively. Bayly and Grein have studied the intermolecular Michael addition of the methoxy anion to methyl vinyl ketone, finding an anti attack angle of 117.9° at the corresponding TS. Therefore, the lower value of the syn attack angle required along the intramolecular 1,4 addition, 96.6°, accounts for the larger energy of TS2-D with respect to TS1-D .…”