21906-08-1Relevant articles and documents
Dynamic Reductive Kinetic Resolution of Benzyl Ketones using Alcohol Dehydrogenases and Anion Exchange Resins
Méndez-Sánchez, Daniel,Mangas-Sánchez, Juan,Busto, Eduardo,Gotor, Vicente,Gotor-Fernández, Vicente
, p. 122 - 131 (2016/01/25)
Dynamic reductive kinetic resolutions of racemic 3-arylalkanones have been performed by the proper combination of an alcohol dehydrogenase and a basic anionic resin. The best results were found for the bioreduction with the alcohol dehydrogenase type A from Rhodococcus ruber DSM 44541 overexpressed in Escherichia coli (E. coli/ADH-A) and the commercially available evo-1.1.200, while the Amberlite IRA-440 C and the DOWEX-MWA-1 resins allowed efficient in situ racemizations. Reaction conditions were optimized in terms of enzyme source and loading, type and amount of resin, pH, temperature and reaction times, obtaining a series of (R,R)-substituted propan-2-ols with good conversions and both diastereoselectivity and stereoselectivity. As a proof of concept, the subsequent intramolecular cyclization of a selected propan-2-ol substrate afforded a valuable isochroman heterocycle without any loss of the optical purity.
Photochemical reactivity of α-phenyl β,γ-enones. Singlet 1,3-acyl shift, triplet aromatic di-?-methane (DPM) rearrangement and triplet aryl-carbonyl bridging
Koppes, Margareth J. C. M.,Beentjes, Peter C. J.,Cerfontain, Hans
, p. 313 - 324 (2007/10/02)
The photochemistry of the series of α-phenyl β,γ-enones 6-10 has been studied under conditions of both direct (λ 300 nm) and triplet-sensitized irradiation with the aim of determining the reactivity patterns of these "multi"-chromophoric systems.Upon direct irradiation, the reactants exhibit the typical photoreactions of β,γ-enones, viz. the 1,3-acyl shift, affording the corresponding (E)- and (Z)-5-phenyl-4-hexen-3-ones, decarbonylation of the radicals formed by α-cleavage and recombination of the resulting alkyl radicals and, in addition, a new type of reaction from the triplet-excited state yielding small amounts of the corresponding acetophenones.The acetophenones are thought to be formed by initial β-bridging between the carbonyl and the phenyl group, followed by extrusion of the C4H6 fragment from the 1,4- or 1,3-oxa-diradical.Upon sensitized irradiation, the o-methoxy- and p-cyano-substituted reactants 9 and 10 exhibit the di-?-methane rearrangement, leading to mixtures of the corresponding cis- and trans-1-acetyl-1-methyl-2-phenylcyclopropanes, with quantum yields of 0.03 and 0.10, respectively.The formation of the 1,3-AS and decarbonylation products illustrates the occurrence of α-cleavage, whereas the acetophenones and di-?-methane products are formed via initial aryl-carbonyl and aryl-vinyl bridging, respectively.The inability of the other α-phenyl β,γ-enones to undergo photocyclopropanation is discussed in terms of excitation-energy partition.In the o-methoxy and p-cyano-substituted reactants, the excitation energy may be predominantly concentrated in the aryl moiety in contrast to the other two systems in which the excitation energy may be mainly localized on the β,γ-enone moiety.Subsequent triplet-energy dissipation by a free-rotor mechanism would then account for the stability of these systems.This was observed for (E)-7 which, upon triplet sensitization, affords only the (Z) isomer, whereas this process is degenerate for the other substrates studied.
