Boryl radical catalysis enables asymmetric radical cycloisomerization reactions.

The development of functionally distinct catalysts for enantioselective synthesis is a prominent yet challenging goal of synthetic chemistry. In this work, we report a family of chiral N-heterocyclic carbene (NHC)-ligated boryl radicals as catalysts that enable catalytic asymmetric radical cycloisomerization reactions. The radical catalysts can be generated from easily prepared NHC-borane complexes, and the broad availability of the chiral NHC component provides substantial benefits for stereochemical control. Mechanistic studies support a catalytic cycle comprising a sequence of boryl radical addition, hydrogen atom transfer, cyclization, and elimination of the boryl radical catalyst, wherein the chiral NHC subunit determines the enantioselectivity of the radical cyclization. This catalysis allows asymmetric construction of valuable chiral heterocyclic products from simple starting materials.

Occupational burnout analysis of border guards in the background of COVID-19 / 中国职业医学

@#Objective To analyze the occupational burnout status and its influencing factors of border guards in the prevention （ - ）Methods and control of coronavirus disease COVID 19 . A total of 1 313 border guards who participate in the prevention and control of epidemic diseases were selected as research subjects using the random cluster sampling method. Military Occupational Burnout Scale and Military Occupational Stress Scale were used to investigate the occupational burnout status and Results occupational stress in the research subjects. The median and 25th and 75th percentiles of military occupational （ ， ） （ ， ）， burnout and occupational stress total scores were 9.0 3.0 15.0 and 76.0 70.0 86.0 respectively. About 73.1% of the subjects were suffered from high occupational stress. The results of multiple linear regression analysis indicated that the higher the scores of interpersonal relationship, military special life, work pressure, unclear role and leadership ability factor in P occupational stress, and the lower the score of personal development, the more serious the occupational burnout (all <0.05 ) ， after excluding the influence of confounding factors; subjects with panic psychology inconvenience caused by closed ， management fear on accountability for poor prevention and no personal hobbies had more serious occupational burnout than （ P ） Conclusion - ， subjects without those factors all <0.05 . In the period of COVID 19 prevention the level of occupational burnout and occupational stress of border guards were generally low. The occupational burnout was mainly affected by occupational stress and fear of the epidemic.