NHC-mediated enantioselectiveformal [4+2] cycloadditions of alkylarylketenes with γ-substituted-β,γ-unsaturated α-ketophosphonates is described. A substrate-dependent switch in diastereoselectivity was observed, with γ-aryl α-ketophosphonates providing preferentially the syn-dihydropyranone-phosphonates and γ-methyl α-ketophosphonates favouring the anti-dihydropyranone-phosphonate. In addition, ketene generation
of obtaining drugs which are able to increase ACh release and consequently to show analgesic and nootropic activities. The results showed that several new compounds are indeed potent analgesics (with an analgesic efficacy comparable to that of morphine) and that the most potent one ((+/-)-19, PG9) also has remarkable cognition-enhancing properties. Our study confirmed that the mechanism of action involves
Stereo‐ and Chemodivergent NHC‐Promoted Functionalisation of Arylalkylketenes with Chloral
作者:James J. Douglas、Gwydion Churchill、Alexandra M. Z. Slawin、David J. Fox、Andrew D. Smith
DOI:10.1002/chem.201503308
日期:2015.11.9
Stereo‐ and chemodivergent enantioselective reaction pathways are observed upon treatment of alkylarylketenes and trichloroacetaldehyde (chloral) with N‐heterocyclic carbenes, giving selectively either β‐lactones (up to 88:12 dr, up to 94 % ee) or α‐chloroesters (up to 94 % ee). Either 2‐arylsubstitution or an α‐branched iPr alkyl substituent within the ketene favours the chlorination pathway, allowing
NHC-Promoted Asymmetric β-Lactone Formation from Arylalkylketenes and Electron-Deficient Benzaldehydes or Pyridinecarboxaldehydes
作者:James Douglas、James E. Taylor、Gwydion Churchill、Alexandra M. Z. Slawin、Andrew D. Smith
DOI:10.1021/jo4003079
日期:2013.4.19
A chiral NHCcatalyzes the asymmetric formal [2 + 2] cycloaddition of alkylarylketenes with both electron-deficient benzaldehydes and 2- and 4-pyridinecarboxaldehydes to generate stereodefined β-lactones. In the benzaldehyde series, optimal product diastereo- and enantiocontrol is observed using 2-nitrobenzaldehyde (up to 93:7 dr (syn:anti) and 93% ee). Substituted 2- and 4-pyridinecarboxaldehydes
Lewis Acid-Promoted Ketene–Alkene [2 + 2] Cycloadditions
作者:Christopher M. Rasik、M. Kevin Brown
DOI:10.1021/ja3103007
日期:2013.2.6
are the first examples of ketene-alkene [2 + 2] cycloadditions promoted by Lewis acids. Notable features of this method include (1) substantial rate acceleration relative to traditional thermal reactions, (2) good diastereoselectivities and yields for the formation of the cyclobutanone products, and (3) inverse diastereoselectivity compared with related thermal cycloadditions for many examples. These