57718-20-4Relevant articles and documents
Computationally Guided Catalyst Design in the Type i Dynamic Kinetic Asymmetric Pauson-Khand Reaction of Allenyl Acetates
Burrows, Lauren C.,Jesikiewicz, Luke T.,Lu, Gang,Geib, Steven J.,Liu, Peng,Brummond, Kay M.
supporting information, p. 15022 - 15032 (2017/10/31)
The Rh(I)-catalyzed allenic Pauson-Khand reaction (APKR) is an efficient, redox-neutral method of synthesizing α-acyloxy cyclopentenones. An enantioselective APKR could provide access to chiral, nonracemic α-acyloxy and α-hydroxy cyclopentenones and their corresponding redox derivatives, such as thapsigargin, a cytotoxic natural product with potent antitumor activity. Rapid scrambling of axial chirality of allenyl acetates in the presence of Rh(I) catalysts enables the conversion of racemic allene to enantiopure cyclopentenone product in a dynamic kinetic asymmetric transformation (DyKAT). A combined experimental and computational approach was taken to develop an effective catalytic system to achieve the asymmetric transformation. The optimization of the denticity, and steric and electronic properties of the ancillary ligand (initially (S)-MonoPhos, 58:42 er), afforded a hemilabile bidentate (S)-MonoPhos-alkene-Rh(I) catalyst that provided α-acyloxy cyclopentenone product in up to 14:86 er. Enantioselectivity of the Rh(I)-(S)-MonoPhos-alkene catalyst was rationalized using ligand-substrate steric interactions and distortion energies in the computed transition states. This asymmetric APKR of allenyl acetates is a rare example of a Type I DyKAT reaction of an allene, the first example of DyKAT in a cyclocarbonylation reaction, and the first catalyst-controlled enantioselective APKR.
Catalytic reduction of phenyl-conjugated acetylenic halides by nickel(I) salen: Cyclization versus coupling
Mubarak, Mohammad S.,Jennermann, Theodore B.,Ischay, Michael A.,Peters, Dennis G.
, p. 5346 - 5352 (2008/03/14)
Cyclic voltammetry and controlled-potential electrolysis were employed to study the catalytic reduction of five phenyl-conjugated haloalkynes by nickel(I) salen electro-generated at carbon cathodes in dimethylformamide containing tetramethylammonium tetrafluoroborate. Electrocatalytic reduction of 7-bromo- and 7-iodo-1-phenyl-1-heptyne affords the carbocyclic product, benzylidenecyclohexane, in up to 41 % yield, whereas under similar conditions reduction of 5-halo-1-phenyl-1-pentyne and 8-bromo-1-phenyl-1-octyne gives benzylidenecyclobutane and benzylidenecycloheptane, respectively, in very low yield (≤1 %). Dimers, alkynes, and alkenynes are other products formed from the phenyl-conjugated haloalkynes. Dimers (diphenylalkadiynes) derived from 5-halo-1-phenyl-1-pentyne and 8-bromo-1-phenyl-1-octyne are obtained in yields ranging from 85 to 93 %, whereas 1,14-diphenyltetradeca-1,13-diyne (the dimer produced from 7-halo-1-phenyl-1-heptyne) is found in yields of 45-51 %. To account for the formation of the various products, a mechanistic scheme that involves phenyl-conjugated alkynyl radicals arising from nickel(I) salen catalyzed cleavage of the carbon-halogen bond of each substrate was formulated. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
