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101.
A chromium-catalyzed pinacol-type cross-coupling reaction between alpha,beta-unsaturated carbonyl compounds and aldehydes is reported. Even sterically demanding substrates could be coupled to afford the corresponding pinacols in good yields. Systematic studies concerning the origin of the diastereoselectivities led to the proposal of a mechanism for this synthetically useful reaction. Acroleins with alpha-branched alkyl side chains were coupled to give the corresponding syn pinacols, while on the other hand, acroleins with less bulky substituents furnished the anti derivatives. The effects of both the substrates and the reagents on the diastereo- and enantioselectivities were investigated. An unexpected catalytic formation of cyclopropanols was found. 相似文献
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Wedel T Gehring T Podlech J Kordel E Bihlmeier A Klopper W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(15):4631-4639
Conjugate additions of nucleophiles (e.g. enolates, amines and malonate anions) to bis(p-tolylsulfinyl)alkenes, alkylidene-1,3-dithiane-1,3-dioxides and alkylidene-1,3-dithiolane-1,3-dioxides have recently been published. Reasons for different selectivities and reaction rates will be discussed by consideration of steric and electronic effects. The preferred mode of attack can be explained by stereoelectronic effects (hyperconjugation) in the primarily carbanion, which is stabilized by n-->S-O-sigma* interaction with an antiperiplanar S=O group. Calculation of the transition states [BP86/aug-TZVP] for the addition of acetone enolate to the dithiane-derived alkylidene bis(sulfoxide) revealed that 6.6-7.3 kJ mol(-1) more energy is needed for an attack leading to a less-stabilized carbanion. Two axial S=O groups in dithiolane-derived alkylidene bis(sulfoxides) lead to a higher reactivity towards nucleophiles. 相似文献
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Chevella Durgaiah Mameda Naresh Macharla Arun Kumar Peraka Swamy Marri Mahender Reddy Kodumuri Srujana 《合成通讯》2016,46(13):1133-1144
A simple, efficient, and environmentally benign protocol for the synthesis of vicinal iodohydrins and iodoesters from olefins using NH4I and Oxone in CH3CN/H2O (1:1) and dimethylformamide (DMF) / dimethylacetamide (DMA), respectively, without employing a catalyst at room temperature is described. Regio- and stereoselective iodohydroxylation and iodoesterification of various olefins with anti fashion, following Markonikov’s rule, was achieved and the corresponding products were obtained in good to excellent yields. In addition, 1,2-disubstituted olefins afforded excellent diastereoselectivity. 相似文献