Aziridines enamines

Af-Vinylaziridine and all the other aziridine enamines are found to exist as equilibrium mixtures of variable compositions, with gauche conformation 24 as the major and a fra .s-bisected form 25 as the minor component54. 

Aziridine enamines of cycloheptanone (12, n = 2) and cyclooctanone (12, n = 3) have been prepared70 by the titanium tetrachloride method, but cyclohexanone gave only compounds 13, 14 and 15. 

Aziridine enamines (16, R = Me, Ph) have been prepared by an aminomercur-ation-demercuration reaction149 (equation 3). 

Addition of aziridine to prop-2-ynyltriphenyl phosphonium bromide (17) give aziridine enamines (18)150-152. 

Two theoretical studies on the structure of aziridine have been published, one relating to the effect of hyperconjugation on the barriers to the inversion of nitrogen and the other to the structures of aziridine-enamines. The reaction by which (270 R = H, Me, or NH2) are hydrolysed to cis- and to trans- 27 ) has been subjected to ab initio calculations. Theoretical predictions have been found to agree with experimental results. 

Primary and secondary amines also react with epoxides (or in situ produced episulfides )r aziridines)to /J-hydroxyamines (or /J-mercaptoamines or 1,2-diamines). The Michael type iddition of amines to activated C—C double bonds is also a useful synthetic reaction. Rnally unines react readily with. carbonyl compounds to form imines and enamines and with carbo-tylic acid chlorides or esters to give amides which can be reduced to amines with LiAlH (p. Ilf.). All these reactions are often applied in synthesis to produce polycyclic alkaloids with itrogen bridgeheads (J.W. Huffman, 1967) G. Stork, 1963 S.S. Klioze, 1975). 

Kwart and Kahn have found that benzenesulfonyl azide forms a complex with freshly reduced copper powder.189 190 This copper azide complex decomposes at a lower temperature than the pure sulfonyl azide. In refluxing methanol, benzene-sulfonamide (27) is isolated as the major product. In the presence of dimethyl sulfoxide, N-benzenesulfonyldimethyl-sulfoximine (28) is obtained in almost quantitative yield. In cyclohexene solution benzenesulfonamide (29), N-benzenesul-fonyl-7-azabicyclo[4.1.0]heptane (30), and 1-cyclohexenylben-zenesulfonamide (31) are isolated as the main reaction products. According to the authors, Schemes VII and VIII represent an acceptable interpretation of the experimental data.189 190 In pure alcohol, the decomposition should occur by two competitive reactions (Scheme VII) producing benzenesulfonamide together with a ketone and oxidized copper. These last two products have indeed been observed in the reaction mixture. In the presence of DMSO, it seems that a copper-nitrene intermediate is formed which is trapped by DMSO. In cyclohexene solution, the authors have observed that the aziridine (30) disappears from the product composition when DMSO is added. The yield of enamine 31, however, is... 

Azomethine ylides can be generated from oxazolidines in the liquid phase by thermolysis and in the gas phase by FVP (90TL6017 92T8947). Depending on the other substituents and the FVP conditions, from 2-isopropyloxazolidines (41) either aziridines or enamines, or a mixture of them, are obtained by ring closure or hydrogen shift of the azomethine ylide. 

Triazoline ring cleavage with nitrogen expulsion can be achieved by photolysis or thermolysis and leads to aziridines, imines, or the isomeric enamines.12 In contrast to thermolysis where product mixtures are obtained, photolysis is more selective and aziridine is the major product.27,79,2 2-290... 

Triazoline thermolysis leads to aziridines, diazo compounds, imines, or enamines a diazonium betaine is postulated as the intermediate that can undergo stabilization by different pathways,16,30,806,112,465 as depicted in Scheme 161. Imine and enamine formation may occur directly from the diazonium betaine806,112,226 237 247 or via the diazo compound.32 Acceleration of the rate of thermolysis of 4,5-dialkyl-substituted triazolines in polar solvents is commensurate with the betaine intermediate,100,112,457,466 and attempts to prove a 1,3-zwitterionic intermediate have failed 467-469... 

Enamine-aziridine formation is also influenced by reaction conditions. Whereas phenyl azide addition to cinnamonitrile at 90°C results exclusively in the enamine,284 thermolysis of the independently synthesized l,5-diaryl-4-cyanotriazoline (Scheme 90) yields a mixture of the aziridine and enamine from phenyl migration.332... 

The enamine appears to be the only product in the reaction of phenyl azide with 1,2-dibenzoylethylene when it is conducted in methanol at room temperature.306 However, when heated under reflux, a mixture of enamine and pyrrolidine along with minor amounts of aziridine is obtained (Scheme 185).306 Hydrogen-bonding interactions are proposed as playing an important role in enamine formation.306,483... 

Triazolines (116), in which there is no free hydrogen on C-4, also thermolyze to aziridines and enamines.67,454 When R is phenyl, regardless of the X substituent, aziridine is the only thermolysis product but when R is alkyl or hetaryl,453 a mixture of aziridine and enamine is obtained, the latter being the predominant product in some cases.67,453 Because enamine formation from the ring-opened diazo isomers does not seem feasible, a diradical intermediate is proposed.67... 

Triazolines with an electron-withdrawing substituent in the 5-position are rare they are obtained as secondary products in the nonregioselective addition of azides to methacrylic derivatives (Scheme 75). Their thermolysis is similar to that of the 4-isomers a mixture of aziridine and enamine is formed.67... 

Catalyt c hydrogenation (palladium or Raney nickel catalyst) surprisingly results in reduction of the carbon-nitrogen single bond rather than the double bond.4,12,40 The imines, or possibly enamines, are usually not isolated and their existence has only been inferred in most instances. Harvey and Ratts have shown that this reaction with azirine (165) does not proceed first to the aziridine which is then reduced to 166, since aziridine (167) is inert to hydrogen and palladium on carbon.40... 

The vast majority of organocatalytic reactions proceeds via covalent formation of the catalyst-substrate adduct to form an activated complex. Amine-based reactions are typical examples, in which amino acids, peptides, alkaloids and synthetic nitrogen-containing molecules are used as chiral catalysts. The main body of reactions includes reactions of the so-called generalized enamine cycle and charge accelerated reactions via the formation of iminium intermediates (see Chapters 2 and 3). Also, Morita-Baylis-Hillman reactions (see Chapter 5), carbene-mediated reactions (see Chapter 9), as well as asymmetric ylide reactions including epoxidation, cyclopropanation, and aziridination (see Chapter 10), and oxidation with the in situ generation of chiral dioxirane or oxaziridine catalysts (see Chapter 12), are typical examples. 

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