- Electrophilic amination of catecholboronate esters formed in the asymmetric hydroboration of vinylarenes
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(S)-(4-Methoxyphenyl)-ethyl-1,3,2-benzodioxaborole, (S)-1-(4-chlorophenyl)ethyl-1,3,2-benzodioxaborole and (S)-1-indanyl-1,3,2-benzodioxaborole, intermediates in the catalytic asymmetric hydroboration of 4-chloro- and 4-methoxystyrene, were isolated as pure oils in 75%, 84% and 49% yield respectively. For the first example, amination with N-chloromagnesio-N-methyl-O-trimethylsilylhydroxylamine gave a mixture of (S)-1-(4-methoxyphenyl)-N- methylethylamine in 33% yield, 88% e.e. and (S)-1-(4-methoxyphenyl) ethanol in 31% yield, 86% e.e.. Related results were obtained in the other cases, and the steps of catalytic hydroboration and amination could be combined in a single sequence without isolation of the intermediate Numerous variants were carried out in the amination procedure with only marginal improvements in chemoselectivity. An investigation of the mechanism was carried out using low temperature heteronuclear NMR on 13C-1-(S)-1-(4-chlorophenyl)ethyl-1,3,2-benzodioxaborole. The dual pathway is a result of an irreversible and unselective initial step.
- Knight, Frances I.,Brown, John M.,Lazzari, Dario,Ricci, Alfredo,Blacker, A. John
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p. 11411 - 11424
(2007/10/03)
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- EXPEDIENT SYNTHESIS OF MONO-TRIMETHYLSILYL HYDROXYLAMINE AND BIS-TRIMETHYLSILYL HYDROXYLAMINE
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Mono and Bis-trimethylsilylhydroxylamine are conveniently prepared by similar procedures on an arbitrarily large scale, without risk or undue effort on the part of the experimenter.
- Bottaro, Jeffrey C.,Bedford, Clifford D.,Dodge, Allen
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p. 1333 - 1336
(2007/10/02)
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- Investigation of Thermally Induced α-Deoxysilylation of Organosilylated Hydroxylamine Derivatives as a General Method for Nitrene Production
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A variety of organosilylated hydroxylamine derivatives have been synthesized and studied as possible nitrene generators by thermally induced α-deoxysilylation: GN(OR')SiR3 GN + R'OSiR3, where G = EtO2C, ArCO, ArSO2, Me, H, and Ph2PO.The methods used to assess nitrene formation include trapping product characterization, substitutent variation, kinetic activation parameter measurements, Hammett studies, and solvent effects.While the latter two types of precursors were only briefly investigated because of their marked resistance to fragmentation, the combined data for the remaining compounds are consistent with the intermediacy of a nitrene.The existence of alternative deoxysilylation pathways is discussed in some cases, and for comparison with the nitrogen systems reported herein, kinetic activation parameters for α-deoxysilylation about carbon and silicon have been determined.
- Chang, Young Hwan,Chiu, Fang-Ting,Zon, Gerald
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p. 342 - 354
(2007/10/02)
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