Thiourea catalysts fluorous

Enantioselective organocatalytic a-chlorination of aldehydes, via enamine catalysis, was independently reported by the groups of MacMillan and Jprgensen in 2004 (Scheme 13.20) [46, 47]. MacMillan utilized his imidazolidinone catalyst and a perchlorinated quinone as the chlorine source, to obtain the S-enantiomer of the a-chloroaldehyde products. Jprgensen employed NCS as the chlorine source, and either a prolinamide catalyst to access the / -enantiomer of the a-chloroaldehyde products, or a Ci-symmetric amine catalyst to access the 5-enantiomer. A recyclable fluorous pyrrolidine-thiourea bifunctional organocatalyst was later employed as an enamine catalyst in this transformation [48]. 

Fluorous thiourea organocatalyst (103) promotes Michael reaction of aldehydes with maleimides in high yield, and ee sometimes >99%. Catalyst (103), easily prepared 0 in one step from readily available materials, can be recovered by filtration and is reusable. 

KOH treatment), or acids after (oxidation with KMnO ). All these transformations took place without decreasing the initial enantiomeric excess, showing the versatility of these compounds [128]. Recently, new fluorous (5)-pyrrolidme-thiourea recoverable catalyst 100 (10 mol%) has been allowed the synthesis of produets 96 in high yields (91-99%) and excellent enantioselectivities (85-92%), with the recovery of the catalysts being possible by fluorous solid-phase extraction [128]. 

A fluorous thiourea organocatalyst 28 was conveniently prepared from a chiral diamine (Scheme 7.29) [45]. The fluorous thiourea 28 catalyzed the Michael reaction of maleimides and aldehydes with high yield and enantioselectivity. The catalyst 28 could be recycled by simple filtration and reused without significant loss of catalytic activity and enantioselectivity, while the catalyst recovery yield dropped dramatically after three cycles. 

Fluorous thiourea conveniently prepared by isothiocyanate perfluorooctyl aniline was also employed in chemoselective oxidation of the sulfide in the presence of 30% HjOj (Scheme 7.30) [46]. The catalyst could significantly shorten the reaction time and improve the product yield. As expected, the catalyst could be easily recovered by fluorous solid-phase extraction and reused for up to five times without significant loss of catalytic activity. 

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