Thioureas desymmetrization

Drivers for Performing Desymmetrization of Thioureas in Micro Reactors... 

Beneficial Micro Reactor Properties for Desymmetrization of Thioureas... 

A single mixing device connected to a stainless steel tube of about 10 m length and 0.25 mm diameter was used [25], The feasibility of performing a nearly spontaneous reaction could be shown. Further studies on the desymmetrization of thioureas showed that for the diphenyl thiourea/cydohexylamine system reasonable reaction... 

Quite recently, we also observed that quinine-based thiourea derivatives showed dramatic concentration and temperature effects on the enantioselectivity in the alcoholytic desymmetrization ofmeso-cyclic anhydrides, which can also be attributed to the self-association of the catalyst [23]. Of course, the possibility that the variation in... 

Recently, 4-substituted prochiral cyclohexanones (10 equiv.) have been efficiently desymmetrized by their reaction with aromatic aldehydes catalyzed by (5)-prohne (1, 20 mol%) in the presence of 3,5-dimethylphenyl 3,5-bisfluoromethylphenyl thiourea as co-catalyst (20 mol%) in toluene at 25°C [53], affording the corresponding aldol products in good yields (68-87%), diastereoselectivities up to 78% de and in high enantioselectivities (94-99% ee). 

A strategy for the desymmetrization of cyclohexadienones via asymmetric aza-Michael reaction using cinchonine-derived thiourea 52 was developed by You s group (Scheme 11.33) [113]. A series of highly enantioenriched bicyclic pyrrolidine and morpholine derivatives were obtained in excellent yields and enantioselectivities. 

Another example of the use of thiourea catalysts in total synthesis was reported by You and coworkers, who obtained (-)-mesembrine by means of an organocata-lyzed aza-Michael addition process (Scheme 44.8) [86]. The crucial step in this route is based on a previous study of the desymmetrization of cydohexadienones performed by the same research group [87]. On this occasion, the difficult task of controlling the sterically congested chiral arylated quaternary carbon center was... 

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