Synthesis of alkyl-and aryldiphenylphosphines via electrogenerated magnesium chloride diphenylphosphanide.

A two-steps procedure allowing the formation of alkydiphenylphosphines and aryldiphenylphosphines in good yield is described. It relies on the electrochemical preparation of magnesium chloride diphenylphosphanide and its subsequent coupling with either alkyl halides or aryl fluorides

Theoretical study to explain how chirality is stored and evolves throughout the radical cascade rearrangement of enyne-allenes

International audienceThis article reports a theoretical study to explain how the intrinsic property of chirality is retained throughout the radical cascade rearrangement of an enantiopure chiral enyne-allene (bearing one stereogenic center) selected as a model for this family of reactions. Calculations at the MRPT2/6-31G(d)//CASSCF(10,10)/6-31G(d) level of theory were used to determine the entire reaction pathway which includes singlet state diradicals and closed-shell species. The cascade process involves three elementary steps, i.e., by chronological order: Myers–Saito cycloaromatization (M-S), intramolecular hydrogen atom transfer (HAT), and recombination of the resulting biradical. The enantiospecificity of the reaction results from a double transmission of the stereochemical information, from the original center to an axis and eventually from this axis to the final center. The first two steps lead to a transient diradical intermediate which retains the chirality via the conversion of the original static chirogenic element into a dynamic one, i.e., a center into an axis. The only available routes to the final closed-shell tetracyclic product imply rotations around two σ bonds (σ(C–C) and σ(C–N), bonds β and α respectively). The theoretical calculations confirmed that the formation of the enantiomerically pure product proceeds via the nonracemizing rotation around the σ(C–C) pivot. They ruled out any rotation around the second σ(C–N) pivot. The high level of configurational memory in this rearrangement relies on the steric impediment to the rotation around the C–N bond in the chiral native conformation of the diradical intermediate produced from tandem M-S/1,5-HAT

Mechanistic Investigation of Enediyne Connected Amino Esters Rearrangement. Theoretical Rationale for the Exclusive Preference for 1,6- or 1,5-Hydrogen Atom Transfer Depending on the Substrate. A Potential Route to Chiral Naphtho-Azepines

International audienceMemory of chirality (MOC) and deuterium-labeling studies were used to demonstrate that the cascade rearrangement of enediyne-connected amino esters 1a and 1b evolved through exclusive 1,5- or 1,6-hydrogen atom transfer, subsequent to 1,3-proton shift and Saito–Myers cyclization, depending on the structure of the starting material. These results were independently confirmed by DFT theoretical calculations performed on model monoradicals. These calculations clearly demonstrate that in the alanine series, 1,5-hydrogen shift is kinetically favored over 1,6-hydrogen shift because of its greater exergonicity. In the valine series, the bulk of the substituent at the nitrogen atom has a major influence on the fate of the reaction. N-Tosylation increases the barrier to 1,5-hydrogen shift to the benefit of 1,6-hydrogen shift. The ready availability of 1,6-hydrogen atom transfer was explored as a potential route for the enantioselective synthesis of naphthoazepines

N-naphthalimide ester derivatives as Type Ⅰ photoinitiators for LED photopolymerization

International audienceIn this study, a series of N-naphthalimide ester derivatives (noted NPIE1-NPIE9) with different substituents were designed as visible light photoinitiators (PIs). These structures exhibited good light absorption properties in the visible range. Photoinitiation abilities of NPIEs were evaluated upon exposure to a light-emitting diode (LED) at 405 nm. All the structures demonstrated good performance during the free radical polymerization of acrylate monomers. Markedly, the function conversion for acrylate monomers in the presence of NPIE1 was higher than that of the benchmark PI diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO). Upon exposure to a LED@455 nm, NPIE1 could also initiate the polymerization of acrylate monomers effectively i.e. the benchmark photoinitiator (TPO) was not efficient for these longer irradiation wavelengths. Through the calculations of the N−O bond dissociation energy and the excited state energy, the cleavage of N−O bond from the singlet state proved to be favorable. Interestingly, CO2 was detected during the polymerization experiments, which indicates that there is a decarboxylation reaction during the photoinitiation process. Based on the obtained results, a mechanism of Type Ⅰ PI behavior can be proposed. Due to the good performance, NPIE1 was successfully used in 3D printing 2 experiments. In addition, high thermal stability of NPIEs in monomers was also found. This can be a great improvement for elaborating stable formulations

Novel Push–Pull Dyes Derived from 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as Versatile Photoinitiators for Photopolymerization and Their Related Applications: 3D Printing and Fabrication of Photocomposites

A series of eleven push–pull chromophores with specific structures have been designed for the free radical polymerization of acrylates, but also for the fabrication of photocomposites and 3D-printed structures. New photoinitiating systems comprising the different push–pull dyes showed excellent photochemical reactivities at 405 nm. Notably, polymerization reactions could be initiated with light-emitting diodes (LEDs) which constitute a unique opportunity to promote the free radical polymerization under mild conditions, i.e., low light intensity (e.g., sunlight) and under air. Photopolymerization is an active research field, and push–pull dyes have already been investigated for this purpose. Besides, it remains of crucial interest to investigate new reactive structures capable of efficiently initiating photopolymerization reactions. The plausible potential of these structures to act as efficient photoinitiators in vat photopolymerization (or 3D printing) and fabrication of photocomposites prompts us to select eleven new push–pull dyes to design multi-component photoinitiating systems activable with LEDs emitting at 405 nm. Precisely, a tertiary amine, i.e., ethyl dimethylaminobenzoate (EDB) used as an electron/hydrogen donor and an iodonium salt used as an electron acceptor were selected to behave as powerful co-initiators to construct three-component photoinitiating systems (PISs) with the different push–pull dyes. Among these new PISs, dye 8 and 9-based PISs could efficiently promote the free radical photopolymerization of acrylates upon exposure to a LED emitting at 405 nm also upon sunlight irradiation, highlighting their huge performance. Photoinitiating abilities could be explained on the basis of steady state photolysis experiments. Fluorescence measurements and electron spin resonance (ESR) spin-trapping experiments were also performed to obtain a deeper insight into the chemical mechanisms supporting the polymerization reaction and determine the way the initiating species, i.e., the radicals, are observed. Finally, two investigated dye-based PISs were applied to the fabrications of photocomposites. Three-dimensional patterns with excellent spatial resolutions were generated by the laser writing technique to identify the effects of photopolymerization of acrylates both in the absence and presence of fillers (silica). Interestingly, comparison between the 3D objects fabricated by the PISs/monomer systems and the PISs/monomer/filler photocomposites indicates that the newly designed photocomposites are suitable for practical applications. View Full-TextThis article belongs to the Special Issue Progression in Photocatalytic Materials for Efficient Performanc

Mechanistic Investigation of Enediyne-Connected Amino Ester Rearrangement. Theoretical Rationale for the Exclusive Preference for 1,6- or 1,5-Hydrogen Atom Transfer Depending on the Substrate. A Potential Route to Chiral Naphthoazepines

International audienceMemory of chirality (MOC) and deuterium-labeling studies were used to demonstrate that the cascade rearrangement of enediyne-connected amino esters 1a and 1b evolved through exclusive 1,5- or 1,6-hydrogen atom transfer, subsequent to 1,3-proton shift and Saito–Myers cyclization, depending on the structure of the starting material. These results were independently confirmed by DFT theoretical calculations performed on model monoradicals. These calculations clearly demonstrate that in the alanine series, 1,5-hydrogen shift is kinetically favored over 1,6-hydrogen shift because of its greater exergonicity. In the valine series, the bulk of the substituent at the nitrogen atom has a major influence on the fate of the reaction. N-Tosylation increases the barrier to 1,5-hydrogen shift to the benefit of 1,6-hydrogen shift. The ready availability of 1,6-hydrogen atom transfer was explored as a potential route for the enantioselective synthesis of naphthoazepines