2- arylaziridines

When DISN reacts with electron-rich styrenes such as p-methoxystyrene, good yields of reduced pyrazines 117, often accompanied by their oxidized forms, are obtained. However, reaction with electron-deficient styrenes like p-fluorostyrene give the 2-amino-3-(2-arylaziridin-l-yl)maleonitriles (118) (72JA3242 84JOC813). 

Further examples, noted too late for inclusion in Table 2, are the preparation of 1- and 2-arylaziridines by the Wenkcr synthesis,[Pg.537]

The Lewis acid-catalysed 3 + 2-cycloaddition of aziridine-2-carboxylates with isocyanates proceeds regio- and stereo-specifically to produce enantiomerically pure 4-substituted imidazolin-2-ones in high yields.33 The reaction of ethyl 7-iodo-2-heptynoate (27), 2-arylaziridines (28), and K2C03 produces polysubstituted indolizidines (30) via an S /formal 3 + 2-cycloaddition (29) process (Scheme 8).34... 

Expansion of aziridines to -lactams. This rhodium complex catalyzes a regio-specific carbonylation of N-f-butyl-2-arylaziridines (1) to form lactams (2). The reaction fails if the alkyl group on nitrogen contains acidic hydrogens adjacent to nitrogen. 

Diiminosuccinonitrile (DISN) (10) reacts exothermically with ds-l,2-dimethoxy-ethylene (62) in acetonitrile to give 5,6-dicyano-2,3-dimethoxy-l,2,3,4-tetrahydro-pyrazine (63) (386, 1596). Styrene and p-halogenostyrenes reacted with DISN in acetonitrile at room temperature to form 2-amino-3-(2 -arylaziridin-r-yl)maleonitrile (64) (50-80%), whereas the more electron-rich p-methoxystyrene and 2-vinylfuran gave 5-aryl-2,3-dicyano-l,4,5,6-tetrahydropyrazine(65)(60-80%).p-Methylstyrene gave both types of products (1597). 

More recently, Takeda et reported [Pd(SlPr)(cin)Cl)] (39) to be highly efficient in the regioselechve and stereospecific cross-coupling of enantiopure 2-arylaziridines with arylboronic acids. Using 4 mol% of the pre-catalyst, a variety of chiral 2-aryl-phenethylamine derivatives were produced under mild reaction conditions in high yield and with excellent enantioselectivity (up to 99% ee, Scheme 17). Electron neutral and electron deficient aziridines and sterically encumbered and/or funchonalized aryl boronic acids were all well tolerated under the developed conditions. 

The benzylic position of 2-arylaziridines is readily lithiated. A-Substituted trans-2,3-diphenylaziridines afford diastereomers according to the solvent used (whether HMPA is present). More dramatic differences are observed in the case of aziridines bearing an oxazoline substituent at C-2. ... 

N-Tosyl-2-aryl-4-pentenylamines Lewis acid-catalyzed opening of ALtosyl-2-arylaziridines in the presence of allyltrimethylsilane gives a mixture of the pentenylamines and 4-aryl-2-trimethylsilylmethylpyrrolidines. A homogeneous product is obtained on treating such a mixture with TBAF. 

The kinetic resolution of aziridines has also been reported. Alper showed that the car-bonylation of N-ferf-butyl- and N-adamantyl-2-arylaziridines in the presence of catalytic amounts of the combination of [Rh(COD)Cl]j and enantiopure menthol produced the corresponding N-alkyl-3-phenylazetidin-2-ones in up to 99.5% optical yield, although the isolated yields were modest. Consistent with the cobalt-catalyzed carbonylation of epoxides and related substrates, inversion of configuration occurs at the site of carbonyl insertion. 

Takeda and Minakata have reported a Pd-catalysed enantiospecific and regi-oselective cross-coupling of 2-arylaziridines with arylboronic acids (Scheme 13.11). The reaction was found to work well with an N-heterocyclic carbene (NHC)-ligated palladium complex, which was able to out-compete p-hydride elimination (Scheme 13.12). This coupling process allowed the preparation of configurationally defined 2-arylphenethylamine derivatives that are otherwise difficult to access in a simple operation by current conventional routes. 

Seheme 13.11 The Pd-catalysed enantiospecific and regioselective cross-coupling of 2-arylaziridines with arylboronic acids. 

A variety of catalysts were explored for the reaction of 2-arylaziridines 20 with CO2 in the absence of other solvents (Scheme 12) [28]. The best results were obtained with zirconyl chloride, which afforded selective formation of 5-aryl-2-oxazolidinones 21. Naturally occurring a-amino acids were also foxmd to be effective catalysts for this reaction [29]. The highest yield and selectivity were observed for L-histidine. The yields and selectivity of the reaction were depended on the conditions and substrate structure. N-Phenyl-substituted aziridine did not react with CO2. 

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