O-Acyl oximes are versatile building blocks being widely applied in organic synthesis, especially for N-heterocycle construction under transition metal catalysis. In the last decade, aza-Heck cyclization using oximes has been progressing in the preparation of functionalized pyrrolines, and instead of Pd catalysis, copper-based catalytic systems were found to work well in some cases. O-Acyl oximes as oxidizing directing groups have attracted intensive attention in transition metal-mediated C-H activation reactions, which avoid the use of external oxidants to feature advantages including mild reaction conditions, higher levels of reactivities, chemo-selectivities, etc. Moreover, catalytic α C(sp(3))-H functionalization of O-acyl oximes and subsequent annulations provide a lot of opportunities for novel N-heterocycle synthesis. These transformations feature certain advantages: diversified and poly-functionalized products, mild and easy handling conditions, oximes serving as an internal oxidant to avoid the use of external oxidants, and so forth.

Chiral nitriles are valuable molecules in modern organic synthesis and drug discovery. Selectively differentiating the two nitrile groups of widely available malononitrile derivatives is a straightforward yet underdeveloped route to construct enantioenriched nitriles. Here we report an enantioselective nickel-catalyzed desymmetrization of malononitriles for the generation of nitrile-containing all-carbon quaternary stereocenters. This protocol involves a nickel-catalyzed addition of aryl boronic acids to alkynes, followed by a selective nitrile insertion, providing unprecedented access to enantioenriched 5−7-membered α-cyanocycloenones with a fully substituted olefin from a broad range of substrates. The synthetic utility of these nitrile products is demonstrated by gram-scale synthesis and conversion to several useful functional groups.

Objectives A multicentre survey was designed to evaluate the impact of COVID-19 outbreak on dental practice worldwide, estimate the COVID-19 related symptoms/signs, work attitudes and behaviour and the routine use of protective measures and personal protective equipment (PPE). Methods A global survey using a standardized questionnaire with research groups from 36 countries was designed. The questionnaire was developed and pretested during April 2020 and contained three domains: 1) personal data; 2) COVID-19 positive rate and symptoms/signs presumably related to the coronavirus; 3) working conditions and PPE adopted after the outbreak. Countries’ data were grouped by the country positive rate (CPR) during the survey period and by Gross-National-Income per capita. An ordinal multinomial logistic regression model was carried out with COVID-19 self-reported rate referred by dental professionals as dependent variable to assess the association with questionnaire items. Results A total of 52,491 questionnaires were returned with a male/female ratio of 0.63. Out of the total respondents, 7,859 dental professionals (15%) reported symptoms/signs compatible with COVID-19. More than half of the sample (n=27,818; 53%) stated to use FFP2/N95 masks, while 21,558 (41.07%) used eye protection. In the bivariate analysis, CPR and N95/FFP2 were significantly associated (OR=1.80 95% CI=1.60/2.82 and OR=5.20 95% CI=1.44/18.80, respectively), while Gross-National-Income was not statistically associated with CPR (OR=1.09 95% CI=0.97/1.60). The same significant associations were observed in the multivariate analysis . Conclusions Oral health service provision has not been significantly affected by COVID-19, although access to routine dental care was reduced due to country-specific temporary lockdown periods. While the dental profession has been identified at high-risk, the reported rates of COVID-19 for dental professionals were not significantly different to those reported for the general population in each country. These findings may help to better plan oral health care for future pandemic events.

A novel route is disclosed for the synthesis of 1,2,4-thiadiazoles starting from amidines, elemental sulfur, and 2-methylquinolines or aldehydes under transition-metal-free conditions. This three-component approach affords efficient and rapid access to 3,5-diaryl substituted 1,2,4-thiadiazoles with good tolerance of a broad range of funcitional groups. Mechanistic studies reveal a radical-involved pathway.

Transition-metal-catalyzed synthesis of N-heterocycles from oximes has been previously well established. In this paper, for the first time a metal-free protocol with the combinational employment of iodine and triethylamine has been demonstrated to be effective to trigger the oxime-based synthesis of pyridines with high chemo-selectivity and wide functional group tolerance. A broad range of functional pyridines were prepared in moderate to excellent yields. While neither iodine nor triethylamine could trigger this transformation, mechanistic experiments indicated a radical pathway for the reaction. The resultant 2-aryl-substituted pyridines have been proved to be versatile building blocks in a range of transition-metal-catalyzed C-H functionalization reactions.