Nosyl aziridines

Jacobsen has utilized [(salen)Co]-catalyzed kinetic resolutions of tenninal epoxides to prepare N-nosyl aziridines with high levels of enantioselectivity [72], A range of racemic aryl and aliphatic epoxides are thus converted into aziridines in a four-step process, by sequential treatment with water (0.55 equivalents), Ns-NH-BOC, TFA, Ms20, and carbonate (Scheme 4.49). Despite the apparently lengthy procedure, overall yields of the product aziridines are excellent and only one chromatographic purification is required in the entire sequence. 

Gold-based catalysis has attracted considerable attention in recent years. A gold-catalyzed aziridination reaction has recently been reported <06JOC5876>. A series of gold catalysts were examined for their ability to catalyze the aziridination of styrene with p-nitrophenylsulfonamide (NsNH2). Styrene and phenyl-substituted styrenes provided the N-nosyl aziridines in good to excellent yields. Cinnamate however provided the aziridine product in only 25% yield. The use of other sulfonamides (e.g. tosyl, trichloroethyl) gave much lower yields of the aziridine product. 

Typically, the stereospecific formation of quaternary centers is as problematic as selective nucleophilic attack at the more substituted carbon of aziridines. Interestingly, a copper mediated methodology has been reported that does both <060L5105>. Although N-tosyl aziridines show favorable results, A-nosyl aziridines gave the best results. The reaction of 89 with a variety of phenols yielded 90 in moderate yields. 

The aziridine ring opening reaction with phenol derivatives using copper(l) acetate (CuOAc)-DBU was reported by Li et al. [51]. Reaction of ethynyl nosyl-aziridine 170 and p-hydroxytyrosine derivative 169 in the presence of DBU (2 equiv.) and a catalytic amount... 

Non-metal catalyzed aziridinations have also been reported. These methods are often more broadly applicable than the metal-catalyzed methods. The use of iV-methylpyrrolidine-2-one hydrotribromide (MPHT) and chloramine-T is an effective route for the synthesis of iV-tosyl aziridines <06MI16>. The aziridination of olefins using i-BuOI and sulfonamides appears to be a general method for aziridination <06CC3337>. The i-BuOI is prepared in situ from t-BuOCl and Nal. This is a broadly applicable method in that a wide variety of sulfonamides (tosyl, nosyl, SES) can be used with roughly equivalent yields. 

In conclusion, the formation of spiro-aziridine only showed efficient selectivity with furan from derivatives. Following a three-step sequence, the (R)-and (5)- spiro-aziridines were prepared in 73% and 30% yield, respectively. Further steps using a N-ortho-nosyl activation/protection system afforded the corresponding endo-spiro-OZTs in overall 20% and 41%, respectively. 

Rhodium perfluorobutyramide, (pfm)4Rh2, has been shown to catalyse the conversion of alkenes to trichloroethoxysulfonyl, nosyl, and tosyl aziridines on reaction with the corresponding sulfonamide and PhI(OAc)2.97... 

As depicted below, alkylation of nosyl amines, such as 36b, can also suffer from competing intramolecular reactions of the Ph3P/DEAD activated alcohol.27 In this instance, rather than giving the expected amino piperidine product 37, alcohol 35 undergoes an intramolecular reaction to form a highly strained aziridine intermediate that then is opened by nosyl amine 36b to give the observed pyrrolidine 38. 

Aziridination of a-trifluoromethyl-substituted acrylates such as 137 can be accomplished with ethyl nosyloxycarbamate. With a weak base such as calcium oxide, a Michael adduct is obtained (138), but with sodium hydride Michael addition is followed by cychzation with extrusion of nosylate ion to give 139. ... 

Ethynyl aziridine 1199 and tyrosine derivative 1200 were coimected to 1201 by ring opening of the aziridine in 90% yield. After removal of the nosyl protecting group, the resulting firee amine was subsequently coupled with A-Cbz valine (for... 

---