Oxidative formation of bis-N-methylquinolinone from anti-head-to-head N-methylquinolinone cyclodimer

The light-driven formation and cleavage of cyclobutane structural motifs resulting from [2 + 2]-pericyclic reactions, as found in thymine and coumarin-type systems, is an important and intensively studied photochemical reaction. Various applications are reported utilizing these systems, among others, in cross-linked polymers, light-triggered drug release, or other technical applications. Herein coumarin is most frequently used as the photoactive group. Quite often, a poor quantum yield for dimerization and cyclobutane-cleavage and a lack of reversibility are described. In this work, we present the identification of a heterogeneous pathway of dimer cleavage found in a rarely studied coumarin analog molecule, the N-methyl-quinolinone (NMQ). The monomer was irradiated in a tube flow-reactor and the reaction process was monitored using online HPLC measurements. We found the formation of a pseudo-equilibrium between monomeric and dimeric NMQ and a continuous rise of a side product via oxidative dimer splitting and proton elimination which was identified as 3,3’-bis-NMQ. Oxidative conversion by singlet oxygen was identified to be the cause of this non-conventional cyclobutane cleavage. The addition of antioxidants suppressing singlet oxygen enables achieving a 100% photochemical conversion from NMQ to the anti-head-to-head-NMQ-dimer. Using dissolved oxygen upon light activation to singlet oxygen limits the reversibility of the photochemical [2 + 2]-cycloaddition and cycloreversion of NMQ and most likely comparable systems. Based on these findings, the development of highly efficient cycloaddition–cycloreversion systems should be enabled.

Are There Only Fold Catastrophes in the Diels–Alder Reaction Between Ethylene and 1,3–Butadiene?

This work revisits the topological characterization of the Diels–Alder reaction between 1,3–butadiene and ethylene. In contrast to the currently accepted rationalization, we here provide strong evidence in support of a representation in terms of seven structural stability domains separated by a sequence of 10 elementary catastrophes, but all only of the fold type, i.e., C₄H₆ + C₂H₄: 1–7– [FF]F[F^†F^†][F^†F^†][FF]F^†–0 : C₆H₁₀. Such an unexpected finding provides fundamental new insights opening simplifying perspectives concerning the rationalization of the CC bond formation in pericyclic reactions in terms of the simplest Thom’s elementary catastrophe, namely the one–(state) variable, one–(control) parameter function.

Are There Only Fold Catastrophes in the Diels–Alder Reaction Between Ethylene and 1,3–Butadiene?

This work revisits the topological characterization of the Diels–Alder reaction between 1,3–butadiene and ethylene. In contrast to the currently accepted rationalization, we here provide strong evidence in support of a representation in terms of seven structural stability domains separated by a sequence of 10 elementary catastrophes, but all only of the fold type, i.e., C₄H₆ + C₂H₄: 1–7– [FF]F[F^†F^†][F^†F^†][FF]F^†–0 : C₆H₁₀. Such an unexpected finding provides fundamental new insights opening simplifying perspectives concerning the rationalization of the CC bond formation in pericyclic reactions in terms of the simplest Thom’s elementary catastrophe, namely the one–(state) variable, one–(control) parameter function.

PLAYING IN THE FRONTIERS OF THE WOODWARD-HOFFMANN RULES

Pericyclic reactions are known for their exquisite selectivity and, in many cases, the formation of multiple chiral centers with a high degree of control. With the advent of accurate computational tools, this control was translated into predictability, and the design and exploitation of this set of reactions opened a new era in organic synthesis. Suddenly, highly complex and profusely decorated polycyclic structures were accessible in relatively short reaction sequences. Out interest in exploring the limits of application of the rules that govern these reactions with ironfist led us to discover a range of eye opening post-transitional effects that are key to ultimately understand reactivity at a microscopic level.

Natural polyenic macrolactams and polycyclic derivatives generated by transannular pericyclic reactions: optimized biogenesis challenging chemical synthesis

Genetically-encoded polyenic macrolactams, which are constructed by Nature using hybrid polyketide synthase/nonribosomal peptide synthase (PKSs/NRPSs) assembly lines, are part of the large collection of natural products isolated from bacteria.

Elucidating the Selectivity of Dyotropic Rearrangements of β-Lactones: A Computational Survey

Dyotropic rearrangement of β-lactones is a neglected treasure in the family of multi-bond reactions and pericyclic reactions. Despite its appealling synthetic potential, the complicate migration selectivity greatly limits its broadwide...