Lewis Base-Promoted Ring-Opening 1,3-Dioxygenation of Unactivated Cyclopropanes Using a Hypervalent Iodine Reagent
作者:Matthew H. Gieuw、Zhihai Ke、Ying-Yeung Yeung
DOI:10.1002/anie.201713422
日期:2018.3.26
A facile and effective system has been developed for the regio‐ and chemoselective ring‐opening/electrophilic functionalization of cyclopropanes through C−C bond activation by [bis(trifluoroacetoxy)iodo]benzene with the aid of the Lewis basic promoter p‐toluenesulfonamide. The p‐toluenesulfonamide‐promoted system works well for a wide range of cyclopropanes, resulting in the formation of 1,3‐diol products
(5R)-7,8:9,10-Di-O-isopropylidene-2,6-dioxa-4-azaspiro[4,5]decan-3-one: a new chiral spirooxazolidin-2-one derived from D-(+)-galactose for use in asymmetric transformations
作者:Malcolm R. Banks、Alexander J. Blake、J. I. G. Cadogan、Ian M. Dawson、Suneel Gaur、Ian Gosney、Robert O. Gould、Keith J. Grant、Philip K. G. Hodgson
DOI:10.1039/c39930001146
日期:——
Starting from D-(+)-galactose, the crystalline spirooxazolidin-2-one 2 can be readily prepared in an optically pure state by a nitrene-mediated four-step sequence, and serves to control both aldol and Diels–Alder reactions with high chiral efficiency, being easy to remove after use.
The Direct, Enantioselective, One-Pot, Three-Component, Cross-Mannich Reaction of Aldehydes: The Reason for the Higher Reactivity of Aldimineversus Aldehyde in Proline-Mediated Mannich and Aldol Reactions
In the proline-mediatedMannich and aldolreactions of propanal as a nucleophile, the aldimine prepared from benzaldehyde and p-anisidine is about 7 times more reactive than the corresponding aldehyde, benzaldehyde, as an electrophile. This higherreactivity of aldimine over aldehyde is attributed to the carboxylic acid of proline protonating the basic nitrogen atom of the aldimine more effectively
BF(3).OEt(2) has been illuminated by successfully demonstrating the unique but highly stereoselectivereactions of hydroxy carbonyl and dicarbonyl substrates. For example, treatment of gamma-hydroxy ketone 1c with BF(3).OEt(2)/Bu(3)SnH in CH(2)Cl(2) at -78 to -40 degrees C afforded the corresponding 1, 4-diol 2c with virtually complete diastereoselection, while use of TiCl(4) as a Lewis acid under similar
Anthracene Cycloadducts as Highly Selective Chiral Auxiliaries
作者:Xiang Liu、John K. Snyder
DOI:10.1021/jo702724t
日期:2008.4.1
A newchiral auxiliary was designed and easily prepared from a Diels−Alder cycloadduct of an enantiomericallypure anthracene with maleimide. Excellent diastereoselectivities in Diels−Alder reactions, conjugateadditions, and aldol reactions employing these auxiliaries are now reported.