Copper-Mediated Trifluoromethylation of α-Diazo Esters with TMSCF<sub>3</sub>: The Important Role of Water as a Promoter
作者:Mingyou Hu、Chuanfa Ni、Jinbo Hu
DOI:10.1021/ja307058c
日期:2012.9.19
Copper-mediatedtrifluoromethylation of α-diazo esters with TMSCF(3) reagent has been developed as a new method to prepare α-trifluoromethyl esters. This trifluoromethylation reaction represents the first example of fluoroalkylation of a non-fluorinated carbene precursor. Water plays an important role in promoting the reaction by activating the "CuCF(3)" species prepared from CuI/TMSCF(3)/CsF (1.0:1
Diastereoselective Synthesis of Tetrahydrofurans by Lewis Acid Catalyzed Intermolecular Carbenoid–Carbonyl Reaction–Cycloaddition Sequences: Unusual Diastereoselectivity of Lewis Acid Catalyzed Cycloadditions
作者:Yuta Hashimoto、Kennosuke Itoh、Akikazu Kakehi、Motoo Shiro、Hiroyuki Suga
DOI:10.1021/jo400858u
日期:2013.6.21
The effects of including metal salts for three. component reactions involving alpha-alkyl-alpha-diazo esters, aromatic aldehydes, and 3-(2-alkenoyl)-2-oxazolidinones are described, in terms of yields and diastereoselectivities. Metal tetrafluorborates (10-30 mol %) such as Co(BF4)(2)center dot 6H(2)O, Ni(BF4)(2)center dot 6H(2)O, and AgBF4 were effective in delivering high yields and diastereoselectivities (93:7 to 99:1) of the corresponding tetrahydrofuran derivatives while suppressing the competitive formation of 1,3-dioxolane. Using (S)-3-(2-alkenoyl)-4-isopropyl-2-oxazolidinones as the dipolarophiles in the three-component reactions, in the presence of Ni(BF4)(2)center dot 6H(2)O or Co(ClO4)(2)center dot 6H(2)O (10-30 mol %), optically active tetrahydrofurans that possess four successive asymmetric centers were synthesized in high diastereoselectivities (99:1). On the basis of the configuration of the cycloadduct using the X-ray analysis, the high diastereoselectivity could be explained by the unusual Re-face approach to the dipolarophile in the presence of the Lewis acid, proceeding through the s-cis conformer of the 3-(2-alkenoyl)-2-oxazolidinone with the two carbonyls in opposing directions (dipole-dipole interaction).