N-Aryl aziridines

Additionally, aziridines can be prepared via a 1,2-amino-leaving group motif generated either in situ or as part of the starting material. For example, an atom economic, direct conversion of epoxides into N-aryl aziridines was reported via the employment of N-arylphosphoramidate anions (14TL5890). Shown below... 

N-Arylation Aziridination Baylis-Hillman reaction Benzoin condensation Bromination... 

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. 

The N-protected-2-aryl aziridines react smoothly with various thiols to afford the corresponding (3-aminosulfides (Fig. 9). In the cleavage of A/-benzyl- and Af-tosyl-2-aryl aziridines, preferential cleavage is at the benzylic position of the aziridine ring, whereas (V-tosyl-2-alkyl aziridines cleaves at the less hindered (terminal) aziridine-ring carbon. 

Aza-allyl-lithium-Verbindungen lassen sich auch durch schwaches Erhitzen der N-Li-thium-Derivate einiger Aryl-aziridine (z.B. 2,3-Diphenyl-aziridin) erhalten und danach bei tiefen Temperaturen mit geeigneten Ethen-Derivaten (z.B. 1,2-Diphenyl-ethen, Phen-ylthio-ethen) zu Pyrrolidinen umsetzen1-2. 

Reaction of diarylcarbodiimides with aziridine 564 give l-(N,N -diarylamidino)-aziridines 565, which rearrange to l-aryl-2-arylamino-2-imidazolines 566 on prolonged heating with potassium iodide. " ... 

N-Unsubstituted aziridines can be elaborated by taking advantage of the nucleophilicity of the nitrogen center. One noteworthy example is the palladium-catalyzed arylation of aziridine 201 with /i-bromonitrobenzene 202 using a... 

Lam and coworkers292 and Antilla and Buchwald297 expanded the scope of this type of catalytic coupling to encompass reactions of amines. Lam reported the coupling of aliphatic and aromatic amines, as well as heterocycles with N—H bonds with a combination of Cu(OAc)2 (10 mol%) and co-oxidants like pyridine A-oxide (PNO) or TEMPO in air. No single set of conditions led to coupling of all substrates. Concurrently, Buchwald reported reactions at room temperature catalyzed by Cu(OAc)2 (5-10 mol%) and myristic acid with stoichiometric amounts of 2,6-lutidine as base. Substituted anilines, as well as primary and secondary amines, reacted with a series of arylboronic acids. Excellent yields of arylated products were obtained for reactions of anilines, but only moderate yields were obtained for reactions of aliphatic amines. Yudin and coworkers employed this protocol to prepare A-aryl aziridines (equation 72)298. 

Indium trichloride induces rearrangement of aryl-substituted epoxides to the respective aryl-substituted acetaldehydes via an exclusive hydride shift As phenyl group migration occurs more readily than hydride migration, stilbene oxide is converted to diphenylacetaldehyde (Scheme 8.140) [184]. N-Tosyl aziridines react smoothly with carboxylic acids in the presence of a catalytic amount of indium triflate to afford the corresponding -aminoacetates and benzoates (Scheme 8.141) [185]. Indium trichloride and indium bromide catalyze regio- and diastereoselective azidolysis, bromolysis, and iodolysis of a, -epoxycarboxylates in water (Scheme 8.142) [186]. 

The distribution of invertomers and the thermodynamic parameters for conformational inversion of C-unsubstituted aziridines have been determined by 250 MHz H n.m.r. spectroscopy. The steric hindrance of the aromatic group in C-aryl-aziridines with other ring substituents was found to be consistent with some form of conjugation between the aromatic system and the aziridine ring. 

An SN2-type ring-opening of N-activated aziridines 105 with a 2-bromobenzyl alcohol/thiol 106, followed by a copper-catalyzed intramolecular N-arylation reaction, afforded the corresponding tetrahydrobenzox(thi)azepines 107 in good yields (14JOC6468). 

As an extension of the direct arylation/N-arylation methodology in the synthesis of phenanthridines, Lautens and Candito [39] attempted the synthesis of indole 124 from iodonaphthalene 122 and a-chloroimine 123 (Scheme 3.31). While the concept was successfully demonstrated, the availability of the a-haloimines was rather hmited because of their challenging syntheses which are often accompanied by decomposition of the imine. To circumvent this problem, the authors decided to employ the highly strained 2H-aziridines 125 as 1,3-dipole equivalents. Optimization studies identified the phosphine hgand P(m-Cl-CgH4), which possessed... 

Wang L, Liu Q B, Wang D Li X, Han X -W, Xiao W -J, Zhou Y -G. Tandem ring-opening/closing reactions of N-Ts aziridines and aryl propargyl alcohols promoted hy I-BuOK. Org. Lett. 2009 11(5) 1119-1122. 

The trans-3,4-dihydro-2//-l,4-benzoxazines could be obtained conveniently by ring opening of aziridines 193 with o-iodophenols 194 and subsequent copper-catalyzed intramolecular N-arylation (Scheme 68) [113]. 

The copper-catalyzed amination developed by Buchwald is an effective method for catalytic coupling of aryl boronic acids with amines [61]. Yudin has recently shown that N-arylation of aziridines is possible under modification of Buchwald s method and is successful with a range of functionalized aryl boronic acids (Scheme 3.41) [62]. 

N-Inversion in azetidine and azetidin-2-one is rapid, even at —77 and -40 °C, respectively (B-73NMR144). Again, halo substituents on nitrogen drastically slow the inversion rate, so that Af-chloro-2-methylazetidine can be separated into two diastereomers (b-77SH(1)54). Substituent effects on N-inversion are much the same as in the aziridines Af-aryl and N- acyl... 

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