Lebel Hélène, Piras Henri
Département de Chimie, Center for Green Chemistry and Catalysis, Université de Montréal, C.P. 6128, Succursale Centre-ville, Montréal, Québec, Canada H3C 3J7.
J Org Chem. 2015 Apr 3;80(7):3572-85. doi: 10.1021/acs.joc.5b00256. Epub 2015 Mar 18.
The synthesis of a variety of chiral sulfilimines and sulfoximines is described. The amination of thioethers with a chiral N-mesyloxycarbamate was achieved in high yields and stereoselectivities using Rh2[(S)-nttl]4 as catalyst in the presence of 4-dimethylaminopyridine (DMAP) and a pyridinium salt, such as bis(DMAP)CH2Cl2 or a viologen salt. These additives proved instrumental to enhance both the yield and the stereochemical discrimination of the reaction. Mechanistic studies and control experiments have elucidated the role of these additives. DMAP served as an apical ligand for the rhodium catalyst: an X-ray crystal structure of the (DMAP)2·[Rh2{(S)-nttl}4] complex was obtained. This complex displayed a lower and irreversible redox potential. Control experiments with preformed Rh(II)-Rh(III) complex suggested such a catalytically active species in the thioether amination process. Diastereoselectivities were influenced by the sulfonyloxy leaving group, ruling out the possibility of a common metal nitrene species and instead suggesting a rhodium-nitrenoid complex. It is believed that the bispyridinium salt played the role of a phase transfer catalyst, influencing both the yield and the diastereoselectivity of the reaction.
描述了多种手性亚磺酰亚胺和亚砜亚胺的合成。在4-二甲基氨基吡啶（DMAP）和吡啶盐（如双（DMAP）CH2Cl2或紫精盐）存在下，以Rh2[(S)-nttl]4为催化剂，硫醚与手性N-甲磺酰氧基氨基甲酸酯的胺化反应以高产率和立体选择性实现。这些添加剂被证明有助于提高反应的产率和立体化学选择性。机理研究和对照实验阐明了这些添加剂的作用。DMAP作为铑催化剂的顶端配体：获得了（DMAP）2·[Rh2{(S)-nttl}4]配合物的X射线晶体结构。该配合物显示出较低且不可逆的氧化还原电位。用预先形成的Rh（II）-Rh（III）配合物进行的对照实验表明，在硫醚胺化过程中存在这样一种催化活性物种。非对映选择性受磺酰氧基离去基团的影响，排除了常见金属氮烯物种的可能性，转而表明存在铑-氮烯类配合物。据信，双吡啶盐起到了相转移催化剂的作用，影响了反应的产率和非对映选择性。
