- On the two-ligand catalytic asymmetric deprotonation of N-Boc pyrrolidine: Probing the effect of the stoichiometric ligand
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(Chemical Equation Presented) To map out the stoichiometric ligand requirements in the two-ligand catalytic asymmetric deprotonation of N-Boc pyrrolidine, 24 different ligands have been evaluated; the highest enantioselectivity (90:10 er) was obtained by using s-BuLi in the presence of 0.3 equiv of (-)-sparteine and 1.3 equiv of a cyclohexanediamine-derived ligand.
- Bilke, Julia L.,O'Brien, Peter
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p. 6452 - 6454
(2008/12/21)
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- Simons electrochemical fluorination of substituted homopiperazines(hexahydro-1,4-diazepines) and piperazines
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Simons electrochemical fluorination (ECF) of 1,4-dimethyl-1,4-homopiperazine, methyl 4-ethylhomopiperazin-1-ylacetate and 1,4-bis(methoxycarbonylmethyl)-1,4-homopiperazine was studied. For comparison, ECF of three piperazines with a N-(methoxycarbonylmethyl) group(s) was also studied. ECF of 1,4-dimethyl-1,4-homopiperazine gave a low yield of corresponding perfluoro(1,4-dimethyl-1,4-homopiperazine) together with perfluoro(2,6-diaza-2,6-dimethylheptane) as the major product. Corresponding perfluoro(homopiperazines) with mono- and/or di-(fluorocarbonyldifluoromethyl) groups [-CF2C(O)F] at the 1- and/or 4-position were formed in low yields from methyl 4-ethylhomopiperazin-1-ylacetate and 1,4-bis(methoxycarbonylmethyl)-1,4-homopiperazine, respectively. These new seven-membered perfluoro(1,4-dialkyl-1,4-homopiperazines) were accompanied by the formation of mono- and/or di-basic linear perfluoroacid fluorides resulting from the C-C bond scission at the 2- and 3-positions of the ring. From mono- and/or di-N-(methoxycarbonylmethyl)-substituted piperazines, corresponding perfluoropeperazines having the acid fluoride group(s) were formed in low yields.
- Abe, Takashi,Baba, Hajime,Fukaya, Haruhiko,Tamura, Masanori,Sekiya, Akira
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- Structural Effects on Photophysical Processes in Saturated Amines. 6. Excited-State Interactions in Piperazine Derivatives
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The spectroscopic and photophysical properties of a series of N,N'-bis(alkyl)piperazine derivatives are reported.On the basis of the photoelectron spectrum of N,N'-dimethylpiperazine (I), and the UV absorption spectra of I, N-methylpiperidine (II), 12,14-diazadecahydroanthracene (III), and 13,14-dimethyl-13,14-diazatricyclo2,7>tetradecane (IV), it is concluded that interaction between the N-n orbitals is nearly absent in the ground state.For I and III, however, fluorescence spectral and lifetime data, when compared with monoamine II, indicate the presence of N-N interaction in the lowest excited state. λmax for I and III are 314 and 315 nm, respectively, while λmax for II is 292 nm.Lifetimes for I and III are significantly longer relative to II (156 and 148 ns vs. 25 ns).Photophysical data for IV imply that upper state N-N coupling is much less significant than for I and III.A comparison of photophysical data for IV and 1,4-dimethylhexahydro-1,4-diazepine (V) is used to suggest that the piperazine nucleus in IV is twisted, resulting in a less efficient through-bond coupling of the locally excited state with the other N center.The fluorescence properties of substituted piperazines, it is suggested, can be used to infer the conformational structure of the cyclohexane ring.
- Halpern, Arthur M.,Ramachandran, B. R.,Sharma, Shobha
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p. 2049 - 2052
(2007/10/02)
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