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131.
Richard Gil 《Tetrahedron》2004,60(13):3085-3090
Samarium diiodide is a catalyst for the reaction of cyclic and acyclic tert-butyldimethylsilyl enoxysilanes with chelating imines. Reaction products are isolated as β-aminoenoxysilanes instead of β-aminoketones as previously observed with the corresponding trimethylsilyl enoxysilanes. Several mechanistic pathways are discussed. 相似文献
132.
Vadim A. Soloshonok Hironari Ohkura Manabu Yasumoto 《Journal of fluorine chemistry》2006,127(7):924-929
DBU-catalyzed asymmetric synthesis of (S)- and (R)-3-amino-4,4,4-trifluorobutanoic acid via enantioselective biomimetic transamination of isopropyl 4,4,4-trifluoro-3-oxobutanoate with (R)- and (S)-phenylethylamine has been developed. The effect of the base concentration of the reaction rate and stereochemical outcome has been systematically studied. The key reaction step, DBU-catalyzed 1,3-proton shift transfer was found to be highly enantioselective (>95% ee). However, due to some racemization of the intermediate Schiff base under the highly basic reaction conditions leads to the final product of lower enantiomeric purity. 相似文献
133.
Santos Fustero Julio Piera Juan F. Sanz-Cervera Raquel Román María Sánchez-Roselló Carmen Ramírez de Arellano 《Tetrahedron》2006,62(7):1444-1451
The condensation of the azaenolates derived from readily available ketimines with fluorinated nitriles offers an efficient and straightforward entry to new fluorinated 1,3-vinylogous amidines. These versatile compounds, in turn, react with triphosgene to yield new fluorinated pyrimidin-2(1H)-ones in high yields. 相似文献
134.
Highly diastereoselective synthesis of cis-β-lactams via [2+2] cycloaddition reactions of imines derived from a chiral bicyclic aldehyde and ketenes is described. The chiral bicyclic aldehyde as well as chiral acids were prepared from commercially available inexpensive isosorbide. The cycloaddition reaction was found to be highly diastereoselective; in some cases giving a single diastereomer of cis-azetidin-2-one in very good yields. A moderate diastereoselectivity was observed with chiral ketenes derived from isosorbide. 相似文献
135.
Jean-Nicolas Desrosiers 《Tetrahedron》2005,61(26):6186-6192
Enantioenriched β-amino alcohols were prepared via an asymmetric addition of diethylzinc, catalyzed by the BozPHOS·Cu(I) complex, on in situ formed N-phosphinoylimines. The nature of the hydroxyl protecting groups was found to affect the enantioselectivities. Subsequent deprotection and oxidation of N-phosphinoyl β-amino alcohols afforded optically active α-amino acids (97% ee). 相似文献
136.
A simple and convenient procedure for reductive amination of aldehydes and ketones using sodium borohydride activated by boric acid, p-toluenesulfonic acid monohydrate or benzoic acid as reducing agent under solvent-free conditions is described. 相似文献
137.
Grzegorz Mlostoń John Warkentin Anthony Linden Heinz Heimgartner 《Helvetica chimica acta》2007,90(10):2024-2036
The reactions of dimethoxycarbene (DMC; 2 ), which was generated in situ by thermal decomposition of 2,5‐dihydro‐2,2‐dimethoxy‐5,5‐dimethyl‐1,3,4‐oxadiazole ( 1 ), with N‐tosylated imines of xanthone and 2,3 : 6,7‐dibenzosuberenone, 3a and 3d , respectively, led to different adducts with rearranged skeletons. In the case of 3a , the 1 : 1 adduct 5 as well as the 2 : 1 adduct 6 were obtained (Scheme 2). The formation of both products can be explained by a migration of a MeO group of the DMC fragment in a zwitterionic intermediate. On the other hand, migration of a Me group of DMC is necessary for the formation of the two 1 : 1 adducts 13 and 14 of 2 and 3d (Scheme 5). The structures of all products have been established by X‐ray crystallography. 相似文献
138.
New active-iron based reducing system for carbonyl compounds and imines. Stereoselective reduction of cyclic ketones 总被引:1,自引:0,他引:1
The reaction of different carbonyl compounds and imines with a mixture of iron(II) chloride tetrahydrate, an excess of lithium powder, and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 5 mol%) in THF at room temperature, led to the formation of the corresponding alcohols and amines, respectively. The process was also applied to the transformation of α,β-unsaturated carbonyl compounds into the corresponding saturated alcohols. The new reducing system exhibited good to excellent diastereoselectivity toward the reduction of different monocyclic and polycyclic ketones. 相似文献
139.
Vitalij V. Levin Young-Hun Song Pavel A. Belyakov Vladimir A. Tartakovsky 《Tetrahedron letters》2008,49(19):3108-3111
Iminium cations generated by the coupling of aldehydes, N-trimethylsilylamines and TMSOTf or by the methylation of imines with MeOTf smoothly react with silanes of a general formula Me3SiRf (Rf = CF3, CCl2F, C6F5) to afford the corresponding tertiary amines having a fluorinated substituent. The key step, involving C-C bond formation, is promoted by NaOAc or KF in DMF as a solvent. 相似文献
140.
Sara Stas 《Tetrahedron》2007,63(36):8921-8931
Potassium phenylethynyltrifluoroborate and potassium styryltrifluoroborates react with α,α-dichlorinated aldimines in the presence of BF3·OEt2 as a Lewis acid to give a new stable class of functionalized propargylamines and allylamines. The use of hexafluoroisopropanol as a co-solvent in this modified Petasis reaction allows high yield isolation of the target compounds. 相似文献