- Formation and characterization of a reactive chromium(V)-oxo complex: Mechanistic insight into hydrogen-atom transfer reactions
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A mononuclear Cr(V)-oxo complex, [CrV(O)(6-COO--tpa)](BF4)2 (1; 6-COO--tpa = N,N-bis(2-pyridylmethyl)-N-(6-carboxylato-2-pyridylmethyl)amine) was prepared through the reaction of a Cr(III) precursor complex with iodosylbenzene as an oxidant. Characterization of 1 was achieved using ESI-MS spectrometry, electron paramagnetic resonance, UV-vis, and resonance Raman spectroscopies. The reduction potential (Ered) of 1 was determined to be 1.23 V vs. SCE in acetonitrile based on analysis of the electron-transfer (ET) equilibrium between 1 and a one-electron donor, [RuII(bpy)3]2+ (bpy = 2,2′-bipyridine). The reorganization energy (λ) of 1 was also determined to be 1.03 eV in ET reactions from phenol derivatives to 1 on the basis of the Marcus theory of ET. The smaller λ value in comparison with that of an Fe(IV)-oxo complex (2.37 eV) is caused by the small structural change during ET due to the dπ character of the electron-accepting LUMO of 1. When benzyl alcohol derivatives (R-BA) with different oxidation potentials were employed as substrates, corresponding aldehydes were obtained as the 2e--oxidized products in moderate yields as determined from 1H NMR and GC-MS measurements. One-step UV-vis spectral changes were observed in the course of the oxidation reactions of BA derivatives by 1 and a kinetic isotope effect (KIE) was observed in the oxidation reactions for deuterated BA derivatives at the benzylic position as substrates. These results indicate that the rate-limiting step is a concerted proton-coupled electron transfer (PCET) from substrate to 1. In sharp contrast, in the oxidation of trimethoxy-BA (Eox = 1.22 V) by 1, trimethoxy-BA radical cation was observed by UV-vis spectroscopy. Thus, it was revealed that the mechanism of the oxidation reaction changed from one-step PCET to stepwise ET-proton transfer (ET/PT), depending on the redox potentials of R-BA.
- Kotani, Hiroaki,Kaida, Suzue,Ishizuka, Tomoya,Sakaguchi, Miyuki,Ogura, Takashi,Shiota, Yoshihito,Yoshizawa, Kazunari,Kojima, Takahiko
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- METHODS FOR PREPARING BIS-TETRAHYDROISOQUINOLINE-CONTAINING COMPOUNDS
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(-)-Jorumycin, ecteinascidin 743, saframycin A and related compounds, methods of preparing the same, formulations comprising the compounds, and methods of treating proliferative diseases with the same are provided.
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Page/Page column 64; 65; 66
(2019/02/06)
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- Regioselective Reductive Alkylation of 3,4,5-Trimethoxybenzaldehyde Dimethylacetal: A New Synthesis of 4-Alkyl-3,5-dimethoxybenzaldehydes and 2,5-Dialkyl-1,3-dimethoxybenzenes
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The regioselective replacement of the 4-methoxy group of 3,4,5-trimethoxybenzaldehyde dimethylacetal by an alkyl group under reductive electron-transfer conditions has been employed as a key step in a new synthesis of 2,5-dialkyl-1,3-dimethoxybenzenes via the corresponding 4-alkyl-3,5-dimethoxybenzaldehydes.
- Azzena, Ugo,Cossu, Sergio,Denurra, Teresa,Melloni, Giovanni,Piroddi, Anna Maria
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p. 313 - 314
(2007/10/02)
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- Ortho Metalation Directed by α-Amino Alkoxides
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The addition of aromatic aldehydes to certain lithium dialkylamides in benzene or tetrahydrofuran gave α-amino alkoxides which were ortho lithiated with excess n-butyllithium.Subsequent alkylation and hydrolysis provided ortho-substituted aromatic aldehydes via a one-pot reaction.The ortho metalation of α-amino alkoxides derived from 1- and 2-naphthaldehyde and various substituted benzaldehydes was examined.When N,N,N'-trimethylethylenediamine was used as the amine component of the α-amino alkoxide, metalation could be carried out at lower temperatures.This rate increase is due to an intramolecular TMEDA-like assisted metalation.The synthetic utility of this ortho metalation, including how varying the amine component of the α-amino alkoxide affects the regiochemistry and metalation rate, is discussed.
- Comins, Daniel L.,Brown, Jack D.
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p. 1078 - 1083
(2007/10/02)
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