Ylids, azomethine

Triazole derivatives also result from the cycloaddition of DEAZD to azomethine ylids derived from electrocyclic ring opening of aziridines.117 121 For example, the tetrahydro-1,2,4-triazole 73 was prepared by thermolysis of the cts-aziridine in the presence of DEAZD in 96% yield (Eq. 8), and... 

Cis- and rranx-cyclopropane-1,2-diamines (both primary and secondary) react with a range of aldehydes, R CHO, to give pyrroles under very mild conditions. NMR has been used to identify the intermediates. The key steps involve ring expansion of the monoiminium ion (22), via an azomethine ylid (23), to yield a dihydropyrrolium ion (24). 

The pyrrolo[l,2-c]imidazole (223) was produced by addition of DMAD to an azomethine ylid resulting from photochemical ring opening of a fused aziridine,299 and the adduct 224 resulted from... 

Some cycloadditions to azirines have been reviewed by Anderson and Hassner.27 Schmid et al. 28 photolyzed the arylazirine 1 in benzene in the presence of 2 equivalents of DM AD and obtained 40% of the pyrrole 3, a compound prepared previously by Huisgen et al.29 30 from oxazolones and sydnones with DMAD. Padwa and his co-workers have investigated the scope of these photoinduced cycloadditions to arylazirines. Irradiation of 1 in pentane for 3 hours in the presence of DMAD gave 95% of (3)31 the azomethine ylid 2 was postulated as an intermediate. 

When the aziridine nitrogen is substituted, Michael-type addition to the acetylene is not possible. Reactions are then usually preceded by ring cleavage with the formation of an azomethine ylid. The product obtained depends on the nitrogen substituent. Heine and co-workers 45,46 used m-l,2,3-triphenylaziridine (27) with DMAD, DEAD, EP, and EPP. The DMAD gave 98% of compound 28 after refluxing in toluene... 

The azomethine ylid 53, generated thermally from the aziridine 52, underwent cycloaddition in near quantitative yield. With DMAD, only one product is possible with EP the sole product was 54, and EPP gave 54 and 55 in 80 20 ratio. This latter result indicates that steric effects are important with the phenylpropiolic ester.52 Nitrones (57) add to benzylideneacenaphthenone (56) forming the spiroisoxazolidines (58), which lose aldehyde fragments on heating or photolysis to give the... 

Winterfeldt and Dillinger58 studied the addition of DEAD to N-benzylaziridine (68) in /-butanol and observed exclusive C—N bond cleavage, leading to compound 69. The reaction is surprisingly facile at room temperature and clearly does not proceed through an azomethine ylid. Interesting reactions take place when the aziridine is a part of a... 

Fusion of an aziridine moiety in a structure which cannot open in a conrotatory fashion inhibits the formation of an azomethine ylid by the thermal process. An example of such a compound is 77 which failed to give cycloadditions up to 180°.50 Oida and Ohki80 irradiated a related compound (78) in dioxane at 15° for 2 hours in the presence of 2 equivalents of DMAD. They obtained 4% of compound 79 and 36% of the isomeric 80 mild alkaline hydrolysis of 79 gave the amorphous 82,... 

The reaction of benzocinnoline iV-oxides (e.g., 497) with excess DM AD for 3 hours at 190° gave low yields of the stable azomethine ylids 499.457 The substrates added to the acetylene in a 1,3-dipolar fashion, a new reaction for azoxy compounds, and an electrocyclic... 

In the ring-opening direction with 4 electrons, we saw a pair of azomethine ylids 2.98 and 2.100 on p. 19, redrawn here as 4.78 and 4.80. These ylids had been produced by heating the aziridines 4.77 and 4.79,... 

Ahnlich verlauft die Umsetzung mit verschiedenen Olefinen, wobei sich das nach C02-Abspaltung entstehende Azomethin-Ylid an ein zweites Olefinmolekiil addieren kann 93>. 

Formylquinoline derivatives (74) have been converted into pyrrolo[3,4-c]quino-lines (76) and (77) by treatment with sarcosine to give azomethine ylids (75), which were then found to undergo spontaneous [l,5]-electrocyclization. Intermediacy of the azomethine ylids has been demonstrated by trapping with N-phenylmaleimide. A possible alternative [l,7]-electrocyclization has not been observed.76... 

The aziridines la, b and the oxazolines 2c, 2d and 2e, bearing at least one electron withdrawing group are thermically in equilibrium with the corresponding azomethine ylids 3 which may be protonated to give the functional iminium salts 4 according to the following scheme (j, 2) ... 

The third area of interest has been the emergence of use of silylmethylamino derivatives as precursors to 1,3-dipolar, non-stabilized azomethine ylids. The ability of the a-aminosilanes to generate the azomethine ylids in the presence of the dipolarophile attracted the attention of organic chemists (See Section VII). 

The same type of azomethine ylid can be obtained from iV-(trimethylsilylmethyl) maleimide. Because this imide is also a dipolarophile, self-condensation takes place leading to the pyrrolo [3,4-a]pyrrolizine skeleton in excellent yield.351... 

A large variety of silylmethylamino derivatives have been shown to be excellent starting materials for the in situ generation of non-stabilized azomethine ylids. Combined with a number of electron-deficient olefinic or acetylenic molecules that have been recognized as good dipolarophiles, ready access to diversely substituted five-membered ring nitrogen heterocycles has consequently been opened. 

The first article on the desilylative route to azomethine ylids appeared in 1979.385 It deals with the action of methyl trifluorosulfonate on iV-(trimethylsilylmethyl)benzylide-nimine to form the corresponding iminium salt which reacts with DMAD in the presence of cesium fluoride to yield corresponding A3-pyrroline. 

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