Olefin complexes aziridination

It has been found that A-tosyl aziridines undergo oxidative addition to palladium complexes to form azapalladacyclobutanes <06JA15415>. Reaction of aziridine 95 with Pd2(dba)3 and 1,10-phenanthroline provides the palladacycle 96 in 45% isolated yield. This compound is an air stable solid. Treatment the palladacycle 96 with catalytic Cul is believed to open the palladacycle to form a copper intermediate, which cyclizes to cyclopentyl alkylpalladium intermediate 97. Loss of Cul then provides the product palladacycle 97 as an air stable solid. Several different aziridines were examined in this reaction. Only a limited set of olefin substituted aziridines provided the azapalladacyclobutanes (e.g. 96). 

Table 6.5 Asymmetric aziridination of rran -substituted styrene derivatives with complex 15 Olefin Conditions Aziridine Yield (%) ee (%)...

The use of polypyrazolylborate copper(I) complexes as catalysts in the conversion of olefins into aziridines 01JOM(617-618)110. 

Asymmetric reactions that can exhibit this type of behavior include atom and group transfer reactions, such as the asymmetric oxidation of sulfides, some asymmetric epoxidations of olefins, " asymmetric aziridination of olefins, - and as)rmmetric cyclo-propanation of olefins. In the asymmetric oxidation of sulfides, a non-racemic, cliiral, low-valent metal complex is oxidized, in this case by iodosobenzene, to generate a highly reactive 0x0 intermediate. The 0x0 is then transferred directly to the sulfur to form the sulfoxide in the enantioselectivity-determining step. A representative example is illustrated in Equation 14.12 that involves a chiral salen-based catalyst. ... 

Addition of carbethoxynitrenes to olefinic double bonds occurs readily. Addition of both the singlet and the triplet species can take place, the former stereospecifically, the latter not 49>. Additions of sulphonyl nitrenes to double bonds have not been demonstrated except in two instances in which metals were present. The reason is that either addition of the starting sulphonyl azide to the double bond occurs to give a triazoline that loses nitrogen and yields the same aziridine as would have been obtained by the direct addition of the nitrene to the olefin, or the double bond participates in the nitrogen elimination and a free nitrene is never involved 68>. The copper-catalyzed decomposition of benzenesulphonyl azide in cyclohexene did give the aziridine 56 (15%), which was formulated as an attack by the sulphonyl nitrene-copper complex on the double bond 24>. 

Recently, Scott et al. have reported that a Cu complex bearing an axially chiral ligand (49) is an excellent catalyst for aziridination of 2,2-dimethylchromene and cinnamate esters (Scheme 36), though it is also less efficient for the reactions of simple olefins.157,158 On the basis of DFT investigation of the nitrenoid intermediate (50), one of the oxygen atoms of the A -sulfonyl group has been proposed to be interacting with the nitrene N-atom.158... 

Kim et al. have reported that the copper complex bearing the unique dinitrogen ligand (51) catalyzes the aziridination of conjugated as well as nonconjugated olefins with good enantio-selectivity (Scheme 37).159... 

Various approaches to epoxide also show promise for the preparation of chiral aziridines. Identification of the Cu(I) complex as the most effective catalyst for this process has raised the possibility that aziridination might share fundamental mechanistic features with olefin cyclopropanation.115 Similar to cyclo-propanation, in which the generally accepted mechanism involves a discrete Cu-carbenoid intermediate, copper-catalyzed aziridation might proceed via a discrete Cu-nitrenoid intermediate as well. 

Bis(oxazoline)-copper complexes 158 have been used by Evans group as chiral catalysts for the enantioselective aziridination of olefins.116 Aryl-substituted olefins have been found to be particularly suitable substrates, which can be efficiently converted to A-tosylaziridines with ee of up to 97% (R = Ph... 

Arylation, olefins, 187, 190 Arylketimines, iridium hydrogenation, 83 Arylpropanoic acid, Grignard coupling, 190 Aspartame, 8, 27 Asymmetric catalysis characteristics, 11 chiral metal complexes, 122 covalently bound intermediates, 323 electrochemistry, 342 hydrogen-bonded associates, 328 industrial applications, 8, 357 optically active compounds, 2 phase-transfer reactions, 333 photochemistry, 341 polymerization, 174, 332 purely organic compounds, 323 see also specific complexes Asymmetric induction, 71, 155 Attractive interaction, 196, 216 Autoinduction, 330 Axial chirality, 18 Aza-Diels-Alder reaction, 220 Azetidinone, 44, 80 Aziridination, olefins, 207... 

Copper complexes catalyze formally related aziridination of olefins with ]7V-(p-toluenesulfonyl)imino]phenyliodinane, a nitrene precursor (219b). As exemplified in Scheme 98, catalysts formed from Cu(I) tri-flate and optically active bis(oxazolines) effect enantioselective reaction of styrene (Scheme 98) (218b, 219a). 

Evans et al. proposed that an imino-copper species in the 3+ oxidation state (Cu3+=NTs) should be the key intermediate in copper-catalyzed aziridinations [75b]. This proposal was supported by Jacobsen s study on the dependence of enantioselectivity on the nitrene precursors and/or the substrate structures with two iminoiodoarenes, PhI=NTs and 2,3,4-Me3-6-(r-Bu)C6HI=NTs), in the presence of CuPF6-33a complex and four olefins [80b]. This study disclosed that enantioselectivity did not depend on the iminoiodoarene, but on the olefins used, that is, the finding excludes the possibility that a Cu-Arl=NTs adduct is a key intermediate. It has also been observed that the photochemical aziridination with tosyl azide (TsN3) catalyzed... 

Triazolines bearing three electron-withdrawing groups (Scheme 85) undergo complex thermolysis reactions. Aziridine formation is observed but sometimes the azide cycloreversion operates pyrrolidines are thus formed by reaction of the olefins with the azomethine ylides from the aziridines. The aziridines also dimerize to piperazines under the conditions of thermolysis.446... 

Silver has three synthetically useful oxidation states Ag(I), Ag(II), and Ag(III).16 Free Ag(III) is very unstable, and most currently known Ag(III) complexes are stablized with electron-donating and/or sterically demanding ligands.17 It is known that Ag(I) can be oxidized to Ag(II) with strong oxidants such as persulfates. Nitrogen-based ligands such as pyridines are commonly used to stabilize high-valence metal ions.18 In 2003, He and coworkers utilized a pyridine-supported silver catalyst and reported the first silver-catalyzed aziridination of olefins.19... 

After successful application of the silver catalyst shown in olefin aziridination (Section 6.1.1), He and coworkers showed that intramolecular amidation was possible with both hydrocarbon-tethered carbamates and sulfamate esters.24 They found that only the Bu3tpy silver complex could catalyze efficient intramolecular amidation, while other pyridine ligands gave either dramatically lower yields or complicated product mixtures. In an interesting control study, both copper and gold were also tested in this reaction. Both the copper and gold Bu tpy complexes can mediate olefin aziridination, but only silver can catalyze intramolecular C-H amidation, indicating that the silver catalyst forms a more reactive metal nitrene intermediate. 

Asymmetric Aziridination of Olefins with Chiral Nitridomanganese Complexes... 

In order to increase the yield and/or the enantioselectivity of the reaction, the reaction temperature and additives were examined. Although aziridination was found to proceed smoothly at 0 °C, the product was not obtained at lower temperatures. Katsuki and co-workers have reported that pyridine /V-oxide is an effective additive for the asymmetric epoxidation catalyzed by salen-manganese(IH) complexes [24], and applied these findings to the asymmetric aziridination of olefins with Phi = NTs [9f]. Thus, the addition of pyridine /V-oxide at 0°C improved the enantioselectivity and allowed the reaction to proceed even at -20 °C (Table 6.1). Other additives, such as 4-phenylpyridine IV-oxide, 4-methylmorphorine N-oxide and 1-methylimidazole were used in the place of pyridine JV-oxide, but positive effects were not observed. 

When 1-phenyl-1,5-hexadiene was treated with complex 15, the chemoselective aziridination proceeded at the olefin portion attached to the phenyl group to give good enantioselectivity (Scheme 21). In other words, unconjugated olefins such as alkyl-substituted olefins were not aziridinated under these conditions. 

---