RESUMEN
4-Substituted catechols with different C[double bond, length as m-dash]C bonds as urushiol analogues were synthesized through the a three-step route including reductive amination reaction of 3,4-dihydroxybenzaldehyde with N-Boc-piperazine, Boc deprotection, and amidation with various fatty acids. Electrochemical polymerization of these analogues on a copper surface afforded robust coatings with desirable adhesive force, hydrophobicity and thermal stability. Cyclic voltammetry and infrared spectroscopic characterizations revealed that the coating formation of urushiol analogues resulted from the electrooxidation-induced radical coupling of phenoxyl radicals with a phenyl ring and the side chain C[double bond, length as m-dash]C bond. The coating of the urushiol analogue bearing only one side chain C[double bond, length as m-dash]C bond exhibited the best performance in copper corrosion inhibition, with an inhibition efficiency of 99.99% and long-term effect (99.9% after 4 weeks of immersion in 3.5 wt% NaCl). The desired performance of these urushiol analogues suggests that they could be of practical applications as an alternative to the resource-limited natural urushiol.
RESUMEN
The chemoselective transformation of diarylethanones via either aerobic oxidative cleavage to give arylmethanoic acids or tandem aerobic oxidation/benzilic acid rearrangement/decarboxylation to give diarylmethanones has been developed. The transformation is controllable and applicable to a broad spectrum of substrates and affords the desired products in good to excellent yields. Mechanistic insights with control reactions, (1)H NMR tracking, and single-crystal X-ray diffraction reveal a complex mechanistic network in which two common intermediates, α-ketohydroperoxide and diarylethanedione, and three plausible pathways are proposed and verified. These pathways are interlinked and can be switched reasonably by changing the reaction conditions. This method enables scalable synthesis and access to a number of valuable compounds, including vitamin B3, diphenic acid, and the nonsteroidal anti-inflammatory drug ketoprofen. The present protocol represents a step forward in exploiting complex mechanistic networks to control reaction pathways, achieving divergent syntheses from the same class of starting materials.