Aziridinations alkenes

Attempts to aziridinate alkenes with iron catalysts in an asymmetric manner have met with only limited success to date [101], In an early report on the use of various chiral metal salen complexes, it was found that only the Mn complex catalyzed the reaction whereas all other metals investigated (Cr, Fe, Co, Ni etc.) gave only unwanted hydrolysis of the iminoiodinane to the corresponding sulfonamide and iodoben-zene [102], Later, Jacobsen and coworkers and Evans et al. achieved good results with chiral copper complexes [103]. 

Benzenetellurinyl acetate (or trifluoioacetate) reacts with alkenes and carbamates under BF3 catalysis to give tt"ons, predominantly Maikovnikov, adducts, conveniently worked up via hydrazine reduction to give tellurides (Scheme 74) The trans nature of (63) was confirmed by indqiendent synthesis from PhTeNa and die rqipropriate aziridine. Alkenic carbamates undergo a much faster intramolecular telluro-lactamization (Sdieme 75) yields are 49-97% over IS varied examples. 

Cyclopropanation and Aziridination (Alkene Three-Membered Cycloadduct) - Cyclopropanation of various trans-N-enoyl derivatives using diazomethane with Pd(OAc)2 as catalyst affords cyclopropyl products with good C(a)-re -facial control (eq 8). Similarly, aziridination with N-aminophthalimide-lead tetraacetate affords N-phthalimidoaziridines with variable but generally good jr-face selectivity (33-95% de). ... 

Aziridines. Alkenes are transfor transfer of the TsN group from TsN = IP CUCIO4 are highly efficient catalysts. 

Electrophilic nitrogen compounds, such as arenesulfonyloxyamines, can convert alkenes to aziridines without the intervention of free nitrenes (80CC560). 

N- Aminoaziridines have been converted to alkenes by reaction with a variety of oxidizing agents (70JA1784). Usually, the deamination reaction is stereospecific. The oxidation of l-amino-2,3-diphenylaziridines with manganese dioxide, however, was not stereospecific. The trans compound gives entirely frans-stilbene, whereas the cfs-aziridine forms a mixture of 85% trans- and 15% c -aikene. cw-Stilbene is not isomerized to trans under the reaction conditions, and the results are explained in terms of an azamine intermediate which can isomerize through a tautomeric equilibrium. 

Alkylaziridines can be stereospecifically deaminated to alkenes by reaction with m-chioroperbenzoic acid (70AG(E)374). The reaction and work-up are carried out in the dark to avoid isomerization of the cw-alkene, and the mechanism is thought to involve an initial oxidation to an amine oxide followed by a concerted elimination. Aziridine oxides have been generated by treating aziridines with ozone at low temperatures (71JA4082). Two... 

Certain N-substituted aziridines are particularly labile towards deamination. N-Aminoaziridines (271) decompose with high stereospecificity to alkenes and diimide between 20 and 60 °C in good yield (70HCA1479). 

Other non-oxidative procedures have also been used to deaminate aziridines. For example, aziridines react with carbenes to yield ylides which subsequently decompose to the alkene. Dichlorocarbene and ethoxycarbonylcarbene have served as the divalent carbon source. The former gives dichioroisocyanides, e.g. (281), as by-products (72TL3827) and the latter yields imines (72TL4659). This procedure has also been applied to aziridines unsubstituted on the nitrogen atom although the decomposition step, in this case, is not totally stereospecific (72TL3827). 

The reaction of carbon atoms with A-unsubstituted aziridines leads to alkenes and hydrogen cyanide (72IA3455), probably via extrusion from the initially formed adduct (285). The fragmentation does not appear to be concerted, although this would be a symmetry-allowed process, since only about half the alkene formed retains the aziridine stereochemistry in the case of cM-2,3-dimethylaziridine. 

Intramolecular alkylnitrene addition to an alkenic moiety situated S,e to the electron deficient center has been utilized for the preparation of bi- and tri-cyclic aziridines (Scheme 11) (68JA1650). Oxidation of the primary alkylamine can be effected cleanly with NCS, LTA or mercury(II) oxide. 

Aziridines have been prepared stereospecifically by the nucleophilic addition of the nitrogen residue to alkenes <80T73). Introduction of the nitrene is accomplished readily via a Michael-type addition with free diphenylsulfilimine (Scheme 12), and where a chiral sulfilimine is used the chirality is transferred to the aziridine with optical yields in excess of 25%. 

Several alkenes are converted to aziridines by treating with oxaziridine (52) at elevated temperatures. Styrene, a-methylstyrene and their derivatives substituted in the benzene ring react smoothly, and so do 1,1-diphenylethylene, indene and acrylonitrile (74KGS1629). 

The mechanism of the reaction is unknown. The stereospecificity observed with (E)- and (Z)-l-methyl-2-phenylethylene points to a one-step reaction. The very low Hammett constant, -0.43, determined with phenylethylenes substituted in the benzene ring, excludes polar intermediates. Yields of only a few percent are obtained in the reaction of aliphatic alkenes with (52). In the reaction of cyclohexene with (52), further amination of the aziridine to aminoaziridine (99) is observed. Instead of diphenylazirine, diphenylacetonitrile (100) is formed from diphenylacetylene by NH uptake from (52) and phenyl migration. 

Oxaziridines unsubstituted at nitrogen as well as some iV-acylated oxaziridines offer synthetic potentialities due to their ability to transfer their nitrogen function to nucleophiles (Section 5.08.3.1.4). The simplicity of preparation of some aziridines from alkenes and the Spiro oxaziridine (S2) equals the simplicity of epoxidation. Aziridine (299), for example, is obtained by simple heating of indene with (52) in toluene (74KGS1629). 

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