Molecular Simulations of Photoaddition Selectivity and Chirality in Challenging Photochemical Reactions

Abstract

The origins of cycloaddition selectivities and chirality controls in particular and challenging photochemical reactions were examined. The profiles of the energies and stereochemical changes of the photoreactions were characterized by molecular simulations using dynamic molecular orbital methods. The photoreactions possess particular factors which are not explained by the frontier molecular orbital (FMO) theory. Particular photoreactions are examined by following the addition selectivities and two chiral controls by use of chiral hosts. The singlet excited state, 1* was inferred to be enantiomeric conformers, 1* (+) and 1* (¹) , and the complex 1¢(l)-21 proceeds to 1* (+) ¢(l)-21, followed by quenching to (R)-20. (5) Sensational chiral isomerization of (Z)-cyclooctene (28Z) to chiral (E)-cyclooctene (29E) by chiral benzenepolycarboxylates (30). 28Z was inferred to accompany asymmetric 28Z and the diastereomeric exciplexes Ex1 (28Z¢30*) and proceeds with chiral isomerization via the one-sided rotation to Ex2 (29E*¢30), followed by quenching to chiral 29E. The molecular simulations for the photoreactions by MOPAC-PM5, (PM3 for hydrogenbonding), UCIS (for singlets), and UB3LYP (for triplets) are found to be successful and show that the origin of the photoreaction selectivities is essentially determined by the first step (TS1) energies and the stereochemistries are dependent on the excited species presented in the Concluding Remarks. We also propose some applications of the molecular simulations.

Molecular Simulation of Hydrogen Bonds, Diels-Alder Reactions, Urethane Formation from Isocyanates andPhotochromism of Dithienylethenes byNew MOPAC2016 Hamiltonians and the Evaluation

“…2.2.1 即ち構造では錯体 , TS, 生成系とも水素結合部の距離 we then simulated basic hydrogen bonds, stereoselective Diels-Alder reactions, practical urethane formation from isocyanates and photochromic cyclization/cycloreversion of references [1] by use of the PM7 levels. The calculated molecular structures and some energies were speculated by experimental data and other ab initio level informations.…”

The structure of electronically excited α,β‐unsaturated lactones

“…In connection with the investigation of the [2 + 2] photocycloaddition of α,β‐unsaturated carbonyl compounds with alkenes and its application to organic synthesis, many mechanistic studies have been carried out in order to understand the origin of the specific reactivity as well as the regio‐ and stereoselectivity in these reactions . Often, the diastereoselectivity of these photochemical reactions is not as high as that in comparable reactions where the furanone reacts in its ground state.…”

Molecular Photochemistry

“…Geometric isomerization is another important type of photoisomerization that involves bond cleavage and creation in alkenes, see Scheme 2. One typical transformation is intramolecular cycloaddition such as [2+2] and [2+3] cycloadditions (Xu et al, 2009;Filley et al, 2001;Lu et al, 2011;Somekawa et al, 2009), which is very attractive in synthetic applications. In addition, the cycloaddition may produce strained and energy-rich products, which has received attention as a way to store solar energy.…”