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许家喜, Yong Liang, Lei Jiao, Shiwei Zhang, and Jiaxi Xu
J. Org. Chem, Vol. 70, No.1, 2005 337,-0001,():
-1年11月30日
Reactions of ketenes generated from R-diazoketones with a series of acyclic and cyclic imines were investigated under both microwave and photoirradiation conditions. The results indicate that the zwitterionic azabutadiene-type intermediates yielded from imines and ketenes undergo a conrotatory ring closure exclusively to produce-lactams. It is notable that no Woodward-Hoffmann product was found under the ultraviolet irradiation. The photoirradiation-induced Staudinger reaction shows a different stereoselectivity from the electrocyclic reaction of substituted 1,3-butadiene.
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许家喜, Jiaxi Xu, Tiezheng Wei, and Qihan Zhang
J. Org. Chem., Vol. 69, No.20, 2004,-0001,():
-1年11月30日
The influence of electronic effects on the enantioselectivity of the oxazaborolidine-catalyzed asymmetric borane reduction of ketones has been observed and investigated with use of parasubstituted acetophenones and propiophenones with a variety of functional groups and Bunsubstituted and B-methoxyoxazaborolidines derived from (S)-2-(diphenylhydroxymethyl)-pyrrolidine with borane and trimethyl borate as catalysts in toluene and THF. The results indicate that Hammett linear free energy electronic effects on the enantioselectivity in the asymmetric reduction were observed and rationalized. Tuning electronic effects of the catalyst can improve the enantioselectivity in the reduction. Another interesting finding to be noted is that anions heavily affect the enantioselectivity, especially for the B-methoxy catalyst, because of their coordination with the boron atom in the catalysts.
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许家喜, Jiaxi Xu, Linge Ma and Peng Jiao
Chem. Commun., 2004, 1616-1617,-0001,():
-1年11月30日
Highly enantioselective aziridination of chalcones catalyzed by a novel backbone 1,8-bisoxazolidiny lanthracene (AnBOX) and CuOTf with up to>9% ee and the opposite enantioselectivity compared with the ligands of Evans are described.
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【期刊论文】A General Route to the Synthesis of N-Protected 1-Substituted and 1,2-Disubstituted Taurines
许家喜, Jiaxi Xu, Shu Xu
Synthesis 2004, No.2, 276-282,-0001,():
-1年11月30日
N-Benzyloxycarbonyl protected substituted and, disubstituted taurines were synthesized from olefins and epoxides via N-benzyloxycarbonylamino alcohol thioacetates as key intermediates. They are important sulfur analogues of naturally occurring amino acids and building blocks for the synthesis of substituted and, disubstituted sulfonopeptides.
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许家喜, Jiaxi Xu, Tiezheng Wei, and Qihan Zhang
J. Org. Chem, Vol. 68, No.26, 2003 10151,-0001,():
-1年11月30日
The effect of temperature on the enantioselectivity of the oxazaborolidine-catalyzed asymmetric borane reduction of ketones has been investigated carefully using alkyl aryl ketones with a variety of functional groups and a B-methoxyoxazaborolidine derived from trimethyl borate and (S)- R,Rdiphenylprolinol as a catalyst. The reductions were carried out over a range of temperatures in THF and toluene with or without the catalyst. The reductive rates increase along with increasing reaction temperature with or without the catalyst by determining the conversion of the ketones to alcohols by GC analysis. However, the rates of the catalytic reductions increase faster than those without the catalyst. The results indicate that the noncatalytic borane reduction is an important factor to the enantioselectivity in the reduction. The highest enantioselectivities were usually obtained between 20 and 30℃ in the asymmetric reduction.
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