Photochemical Elimination of Leaving Groups from Zwitterionic Intermediates Generated via Electrocyclic Ring Closure of α,β-Unsaturated Anilides

Abstract

Methacrylanilides, ArN(CH3)COC(CH2LG)=CH2, with allylic leaving groups (LG(-) = BocAla, PhCO2(-), PhCH2CO2(-), PhO(-)) undergo photochemical electrocyclic ring closure to produce a zwitterionic intermediate. Further reaction of the intermediate results in expulsion of the leaving group to give an alpha-methylene lactam as the major product. In addition, a lactam product that retains the leaving group is formed via a 1,5-H shift in the intermediate. Elimination of the leaving group is generally preferred, even for LG(-) = PhO(-), although in benzene as the solvent the lactam retaining the phenolate group becomes the sole photoproduct. The electrocyclic ring closure occurs in the singlet excited-state for the para-COPh-substituted anilide derivative and is not quenched by 0.15 M piperylene or 0.01 M sodium 2-naphthalenesulfonate (2-NPS) as triplet quenchers. Comparable concentrations of 2-NPS strongly quench the transient absorption of the triplet excited state observed at 450-700 nm according to laser flash photolysis experiments. In aqueous media, quantum yields for total products are insensitive to leaving group ability, and Phi(tot)(para-CO2CH3) = 0.04-0.06 at 310 nm and Phi(tot)(para-COPh) = 0.08-0.1 at 365 nm, for which Phi(isc) = 0.15.

Waveguiding Microactuators Based on a Photothermally Responsive Nanocomposite Hydrogel

“…The reaction was conducted under 80 °C for 15 h after three freeze‐pump‐thaw cycles and a nitrogen purge for 15 min. The generated polymer was precipitated and washed with diethyl ether by filtration and finally dried in a vacuum oven for 24 h. Acrylamidobenzophenone was synthesized via reaction of acryloyl chloride and 4‐aminobenzophenone in dichloromethane and trimethylamine as described in previous report . AIBN was purified by recrystallization.…”

Random photografting of polymers to nanoparticles for well‐dispersed nanocomposites

“…To demonstrate the utility of the benzyl ether ligand for photografting of polymers, we prepare several copolymers containing 3–5 mol % of BP‐acrylamide as a comonomer via free radical polymerization, following reported methods . The synthesis of BMPE and NPs are described in the “Experimental” section.…”

“…Statistical copolymers containing pendent benzophenone (BP) units were used for solution‐state ultraviolet (UV) grafting, thereby providing a simple means to control graft density through variations in exposure dose. The photochemistry of BP is well studied, and it can be easily modified to yield monomers, including (meth)acrylates and acrylamides, suitable for polymerization by a wide range of methods.…”

Dual Action Antimicrobial Surfaces: Alternating Photopatterns Maintain Contact‐Killing Properties with Reduced Biofilm Formation

“…BPAm was prepared according to a modified literature procedure. [ 38 ] Briefly, 4‐aminobenzophenone (5 g, 25.4 mmol) and triethylamine (4.25 mL, 30.5 mmol) were added to a round‐bottomed flask and dissolved in dichloromethane (40 mL) on ice. Acryloyl chloride (2.3 mL, 27.9 mmol) in dichloromethane (10 mL) was added slowly dropwise to the stirred solution.…”