53723-94-7Relevant articles and documents
Steric/π-Electronic Insulation of the carbo-Benzene Ring: Dramatic Effects of tert-Butyl versus Phenyl Crowns on Geometric, Chromophoric, Redox, and Magnetic Properties
Listunov, Dymytrii,Duhayon, Carine,Poater, Albert,Mazères, Serge,Saquet, Alix,Maraval, Valérie,Chauvin, Remi
, p. 10699 - 10710 (2018)
Hexa-tert-butyl-carbo-benzene (C18tBu6) and three phenylated counterparts (C18tBumPh6?m; m=4, 2) have been synthesized. The peralkylated version (m=6) provides experimental access to intrinsic features of the insulated C18 core independently from the influence of π-conjugated substituent. Over the series, structural, spectroscopic, and electrochemical properties are compared with those of the hexaphenylated reference (m=0). Anchoring tBu substituents at the C18 macrocycle is shown to enhance stability and solubility, and to dramatically modify UV/Vis absorption and redox properties. Whereas all carbo-benzenes reported previously were obtained as dark-reddish/greenish solids, crystals and solutions of C18tBu6 happen to be yellow (λmax=379 vs. 472 nm for C18Ph6). In comparison to C18Ph6, the reduction of C18tBu6 remains reversible, but occurs at twice as high an absolute potential (E1/2=?1.36 vs. ?0.72 V). Systematic XRD analyses and DFT calculations show that the C18 ring symmetry is the nearest to D6h for m=6, which indicates a maximum geometric aromaticity. According to calculated nucleus-independent chemical shifts (NICS), the macrocyclic magnetic aromaticity is also maximum for C18tBu6: NICS(0)=?17.2 ppm versus (?18.0±0.1) ppm for the theoretical references C18H6 and C18F6, and ?13.5 ppm for C18Ph6. Accurate correlations of NICS(0) with experimentally recorded or calculated maximum UV/Vis absorption wavelengths, λmax, and chemical hardness, η=ELUMO?EHOMO, are evidenced.
The Ever-Elusive Tetra-ferf-butylethene (TTBE, 3,4-Di-ferf-butyl- 2,2,5,5-tetramethylhex-3-ene): Further insight on its preparation
Klein, Oliver,Hopf, Henning,Grunenberg, Jorg
scheme or table, p. 2141 - 2148 (2009/09/06)
Diketone 4 was prepared by hydrolysis of hexendiyne 5,the latter being available through McMurry coupling of acetyl- enic ketone 26. Upon treatment with dimethyltitanium dichlo- ride, 4 cyclizes into fully alkylated furan derivative 30;the still unknown t
Asymmetric reduction of ethynyl ketones and ethynylketoesters by secondary alcohol dehydrogenase from Thermoanaerobacter ethanolicus
Heiss, Christian,Phillips, Robert S.
, p. 2821 - 2825 (2007/10/03)
Secondary alcohol dehydrogenase (SADH) from Thermoanaerobacter ethanolicus, an NADP-dependent, thermostable oxidoreductase, reduces ethynyl ketones and ethynylketoesters enantioselectively to the corresponding propargyl (propargyl = prop-2-ynyl) alcohols. Ethynyl ketones, in general, are reduced with moderate enantioselectivity (with the exception of 4-methylpent-l-yn-3-one, which gives the (S)-alcohol with >98% ee). Although ethynyl ketones bearing a small (up to n-propyl) alkyl substituent are reduced to (S)-alcohols, larger ethynyl ketones give (R)-alcohols. In contrast, ethynylketoesters are converted to (R)-ethynylhydroxyesters of excellent optical purity. Unexpectedly, isopropyl ethynylketoesters give higher chemical yields and higher enantioselectivities of ethynylhydroxyesters than methyl or ethyl ethynylketoesters. The optically pure ethynylhydroxyesters may serve as useful chiral building blocks for asymmetric synthesis.
