TRANSTION METAL MEDIATED CARBON-HETEROATOM AND CARBON-CARBON BOND FORMATION: STUDIES IN MULTICOMPONENT COUPLING REACTIONS AND RING-CLOSING METATHESIS

Pd(PPh3)4 catalytically assembles sulfenamide (PhS-NR2), alkyne, carbon monoxide and diphenyl diselenide in a one-pot four component coupling reaction to yield (Z)-â-selenyl acrylamides. The reaction proceeds in good to excellent yield (60-95%) and is tolerant of a wide range of functional groups on both the nitrogen of the sulfenamide and the alkyne. Moderate selectivities ranging from 4:1 to 7:1 â-selenyl to â-sulfenyl acrylamide have been observed despite the initial concentration of 2:1 selenium to sulfur in the reaction. The chalcogeno selectivity was found to depend directly on CO pressure; increased CO pressure decreased selectivity for selenium over sulfur.The azaselenolation of carbon monoxide by sulfenamide is catalyzed by RhCl(CO)(PPh3)2 to give Se-aryl selenocarbamates. The reaction proceeds in moderate to good yield (71-89%) and exhibits a 9:1 selectivity for the formation of seleno- over thiocarbamate despite the initial 1.4:1 concentration of selenium to sulfur in the reaction. Selectivity is postulated to arise from the more favorable oxidative addition of diphenyl diselenide to rhodium relative to diphenyl disulfide. Also discussed is the effect of several transition metal complexes on the yield and selectivity of the azaselenolation reaction and our attempts to develop a transition metal catalyzed olefin azasulfenylation reaction.Imine-olefin ring-closing metathesis of á,ù imino-olefins with Schrock-type alkylidene complexes, Mo(=CHR)(=NAr)(OR')2 is discussed. Ring-closing proceeded to yield the target substrate 2H-chromene in 63% yield. Mechanistically, it was determined that the reaction operates under kinetic control via initial alkylidene-olefin metathesis followed by ring-closing alkylidene-imine metathesis

Genomic epidemiology of SARS-CoV-2 in a UK university identifies dynamics of transmission

AbstractUnderstanding SARS-CoV-2 transmission in higher education settings is important to limit spread between students, and into at-risk populations. In this study, we sequenced 482 SARS-CoV-2 isolates from the University of Cambridge from 5 October to 6 December 2020. We perform a detailed phylogenetic comparison with 972 isolates from the surrounding community, complemented with epidemiological and contact tracing data, to determine transmission dynamics. We observe limited viral introductions into the university; the majority of student cases were linked to a single genetic cluster, likely following social gatherings at a venue outside the university. We identify considerable onward transmission associated with student accommodation and courses; this was effectively contained using local infection control measures and following a national lockdown. Transmission clusters were largely segregated within the university or the community. Our study highlights key determinants of SARS-CoV-2 transmission and effective interventions in a higher education setting that will inform public health policy during pandemics.</jats:p