Nitrenes reactions with enamines

V-Aminopyrroles, easily prepared from the reaction of azoalkenes with enamines and /3-dicarbonyl compounds, have been shown to react with electron deficient alkynes to afford substituted benzenes (79TL2969). While the N-methoxycarbonylaminopyrrole (208) reacted with DM AD under rather vigorous conditions to afford (211) in only 13% yield, the N-unsubstituted aminopyrrole (209) prepared from (208) by NaCN treatment reacted with DMAD in CHC13 solution at room temperature to give (211) in 50% isolated yield. The formation of the aromatic system probably occurs by extrusion of the heteroatom bridge from (210) to afford a relatively stable nitrene (212 Scheme 45). 

The 1,3-diazines have also been prepared by a reaction of enamines and S, S -dimethyl-A (A arylbenzimidoyl)sulfimides 360 in boiling tetraline220,221. The mechanism of the ring formation probably involves a thermal cleavage of the imidoylsulfimides 360 into imidoylnitrenes 361 and dimethyl sulfide. The nitrene can then react with the enamine to give an aziridine intermediate 362 which rearranges to a 3,4-dihydroquinazoline 363. Subsequent elimination of amine yields the quinazoline 364220. 

The reaction of ethoxycarbonyl nitrene, generated by decomposition of the azide or by the a-elimination method, with enamines gave mixtures of aminimides and a-amino ketone derivatives30.. V-Methoxycarbonyl. A -cyano and N-sulfonyl azides reacted with 1,2-31 and 1,4-dihy-dropyridines32 to afford directly the corresponding aziridines 9 and 10. The configuration of the aziridine 10, relative to the R substituent, was not determined. 

Alkyl-2-phenylquinazolines 9 are readily available by reaction of 5,S -dimethyl-A-(A-aryl-benzimidoyl)sulfimides 7 with enamines 8 in refluxing Tetralin (1,2,3,4-tetrahydronaphthalene). The mechanism of quinazoline ring formation probably involves a thermal cleavage of the imidoylsulfimides into imidoyl nitrenes, nitrene addition to the enamine double bond and subsequent rearrangement of the aziridine intermediate thus formed to the final product 9. Small amounts (10-15%) of 4-unsubstituted quinazolines 10 are obtained as byproducts. The formation of these byproducts involves a known intramolecular rearrangement of the benz-imidoylsulfimides employed. ... 

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... 

Better yields, but lower enantiomeric excesses, were obtained by an alternative method, the cycloaddition of ethoxycarbonyl azide, followed by irradiation to give the aziridine64. Interestingly, the opposite configuration at the stereogenic center was formed by the two methods. The enantiomeric excess of the product was determined by ketalization with (2/, 3/ )-2,3-butanediol and GC or l3C-NMR analyses of the reaction mixture. The choice of the chiral auxiliary is crucial unfortunately, the enamine derived from //ww-2,5-dimethyl pyrrolidine does not react with either the nitrene or the azide. 

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