Lignin pyrolysis leads to the formation of diverse phenolic products that bear structural similarities to natural lignin,and the related mechanism has been widely explored based on the linkage cleavageinvolved reactio...Lignin pyrolysis leads to the formation of diverse phenolic products that bear structural similarities to natural lignin,and the related mechanism has been widely explored based on the linkage cleavageinvolved reactions.However,some unusual pyrolytic products exhibiting significant structure deviations from lignin,such as aldehydes,remain obscure in mechanism due to long-standing neglect of their formation pathways.The present work found the pivotal role of aryl migration,a special radical-mediated rearrangement process,in governing the formation of these atypical products for the first time.Herein,density functional theory calculations,electronic structure analyses,and pyrolysis experiments were combined to investigate rearrangement patterns and prerequisite structural characteristics of aryl migration by employing typical radicals derived from linkages and substituents of lignin as models.The results indicate that the radical with an unpaired electron located on the second atom of the aromatic side chain can undergo three-membered aryl 1,2-migration triggered by exo cyclization with the best superiority,determining the generation of aldehydes,alkenes,and other products through subsequent cleavage reactions.A clear correlation among the initial geometric and electronic structures of lignin,the patterns and types of aryl migration,the energy barriers,and the end products was established.This study contributes to systematically elucidating rearrangement mechanisms and constructing a more comprehensive lignin pyrolysis mechanism network.展开更多
Our present study unveils a new and efficient N-heterocyclic carbene(NHC)-boryl radical-catalyzed cycloisomerization of N-(2-ethynylaryl)arylamides.This catalytic process is triggered by the addition of an NHC-boryl r...Our present study unveils a new and efficient N-heterocyclic carbene(NHC)-boryl radical-catalyzed cycloisomerization of N-(2-ethynylaryl)arylamides.This catalytic process is triggered by the addition of an NHC-boryl radical to the alkynyl moiety,followed by a radical cascade comprising of an intramolecular cyclization,successive 1,5-and 1,2-aryl migrations,and the reorganization of a C–C triple bond.展开更多
基金supported by the National Natural Science Foundation of China,China(52436009,52276189)the Postdoctoral Fellowship Program of CPSF,China(GZB20230207)the Fundamental Research Funds for the Central Universities,China(2024JC001,2024MS087)。
文摘Lignin pyrolysis leads to the formation of diverse phenolic products that bear structural similarities to natural lignin,and the related mechanism has been widely explored based on the linkage cleavageinvolved reactions.However,some unusual pyrolytic products exhibiting significant structure deviations from lignin,such as aldehydes,remain obscure in mechanism due to long-standing neglect of their formation pathways.The present work found the pivotal role of aryl migration,a special radical-mediated rearrangement process,in governing the formation of these atypical products for the first time.Herein,density functional theory calculations,electronic structure analyses,and pyrolysis experiments were combined to investigate rearrangement patterns and prerequisite structural characteristics of aryl migration by employing typical radicals derived from linkages and substituents of lignin as models.The results indicate that the radical with an unpaired electron located on the second atom of the aromatic side chain can undergo three-membered aryl 1,2-migration triggered by exo cyclization with the best superiority,determining the generation of aldehydes,alkenes,and other products through subsequent cleavage reactions.A clear correlation among the initial geometric and electronic structures of lignin,the patterns and types of aryl migration,the energy barriers,and the end products was established.This study contributes to systematically elucidating rearrangement mechanisms and constructing a more comprehensive lignin pyrolysis mechanism network.
基金This work was supported by the National Natural Science Foundation of China(21672195 and 21702201)the Fundamental Research Funds for the Central Univer-sitiesthe University of Science and Technology of China.
文摘Our present study unveils a new and efficient N-heterocyclic carbene(NHC)-boryl radical-catalyzed cycloisomerization of N-(2-ethynylaryl)arylamides.This catalytic process is triggered by the addition of an NHC-boryl radical to the alkynyl moiety,followed by a radical cascade comprising of an intramolecular cyclization,successive 1,5-and 1,2-aryl migrations,and the reorganization of a C–C triple bond.
