Deciphering Stereoselectivity in Hurd-Claisen Rearrangements: A Comprehensive Study of Electrostatic Interactions from Shubin's Energy Decomposition Analysis.

In this study, we explore the stereoselectivity of Hurd-Claisen Rearrangements, focusing on the influence of two electron-withdrawing groups and eight diverse substituents. Utilizing the Curtin-Hammett principle, we performed energy calculations for reactions, products, and transition states using the M062X/def2TZVPP compound model. Our analysis reveals that kinetic factors predominantly dictate the reaction equilibrium. A key aspect of our research is the application of Shubin's energy decomposition analysis to optimized transition states, highlighting the significant role of electrostatic interactions in determining stereoselectivity. We further dissected each transition state into four fragments: the electron-withdrawing groups ($CO_2Et$, $CN$), the Hurd group ($H$), various substituents ($CH_3$, $Et$, $SProp$, $TBut$, $IsoBut$, $NH_2Ph$, $NO_2Ph$, $Ph$), and the central fragment. This fragmentation approach enabled an in-depth analysis of group dipole moments, providing insights into the electrostatic forces at play. Our findings shed light on the intricate mechanisms driving stereoselectivity in Hurd-Claisen Rearrangements and enhance the understanding of molecular interactions, offering valuable implications for organic synthesis.

Non-covalent interactions and their impact on the complexation thermodynamics of noble gases with methanol.

Accurate ab initio calculations provide the reliable information needed to study the potential energy surfaces that control the non-covalent interactions (NCIs) responsible for the formation of weak van der Waals complexes. In this work, relying on the state of the art method for NCI computations, namely symmetry adapted perturbation theory (SAPT), we calculated the potential energy curves for the interaction of noble gases (Ng = He, Ne, Ar and Kr) with methanol in three different interaction sites to account for orientational anisotropy of the interaction potential. Different levels of the SAPT and basis set were employed to disclose the nature of the stabilizing forces acting upon formation of the Ng-CH3OH adducts. SAPT-derived NCIs indicate that dispersion forces are indeed the dominating component of the total energy, but also that induction and electrostatic effects are important to counterbalance the steric repulsions. By solving the Radial Nuclear Schrödinger Equation for the complexes, we also determined the rovibrational structure of the interaction wells to extract invaluable information about the thermodynamic stability of the adducts and how different temperature conditions affect the structure of the dimers. Although SAPT calculations reveal net attractive forces, these do not afford a spontaneous complexation process even at temperatures as low as 40 K.

Unprecedented E-stereoselectivity on the sigmatropic Hurd-Claisen rearrangement of Morita-Baylis-Hillman adducts: a joint experimental-theoretical study.

Herein we report the first systematic investigation of the tandem mercury(ii) catalysed transvinylation/Hurd-Claisen rearrangement of MBH adducts derived from alkyl acrylates. This is the first report of E-selectivity for MBH adducts with alkyl side chains and is complementary to the previously reported Johnson-Claisen and Eschenmoser-Claisen rearrangements. The rearrangement products were obtained in good yields and could be readily converted to 2-alkenyl δ-valerolactones. Combined DFT and F-SAPT studies demonstrate that reaction rates are primarily governed by non-covalent interactions dictating the relative stability of the transition states. Our F-SAPT calculations revealed that the hyperconjugative effects are not so significant, but that electrostatic interactions, instead, are the driving forces for the relative E : Z stereoselectivity.