Azomethine imide

Simple criss-cross cycloadditions described so far are in fact limited to aromatic aldazines and cyclic or fluorinated ketazines. Other examples are rather rare, including the products of intramolecular criss-cross cycloaddition. The criss-cross cycloadditions of hexafluoroacetone azine are probably the best studied reaction of this type. It has been observed that with azomethine imides 291 derived from hexafluoroacetone azine 290 and C(5)-C(7) cycloalkenes < 1975J(P 1)1902, 1979T389>, a rearrangement to 177-3-pyrazolines 292 competes with the criss-cross adduct 293 formation (Scheme 39). 

A -Iminoazolium betaines, like all azomethine-imides, take part in 1,3-dipolar cycloadditions with various dipolarophiles activated acetylenes... 

Barlow, M.G. Suliman, N.N.E. Tipping, A.E. Unsaturated nitrogen compounds containing fluorine. Part 18. Novel cycloaddition products from the reaction of quadricyclane with fluorinated azines and the azomethine imide 2-hexafluoroisopropylidene-3-methyl-3-phenyl-5,5-bis(trifluoromethyl)tetrahydropyrazol-2-ium-l-ide. J. Fluorine Chem. 1995, 72(1), 147-156. 

N2OC2 Acylamidines Acylamidinium chlorides Acylcyanamides Acylhydrazones N-Acylnitrilimines a,a-Alkoxyaminonitriles 1 -Alkoxycyanamides Aminomethoximes Azomethine imides Azine monoxides Carbamyl cyanides N -Cyaniminoesters Cyanoformamides... 

The 1,3-dipolar cycloaddition of pyrazolidinone-based dipoles (azomethine imides) to terminal alkynes with electron-withdrawing groups, promoted by the dinuclear copper complex [Cu(p-OH)(tmen)]2Cl2 =... 

Stable heterocyclic five-member azomethine imines, azolium fV-imides, tria-zolium and pyrazolidinium ylides 98H(49)587. 

Microwave-induced 1,3-dipolar cycloadditions involving azomethine ylides have been widely reported in the literature. Bazureau showed that imidates derived from a-amino esters 120, as potential azomethine ylides, undergo 1,3-dipolar cyclo-additions with imino-alcohols 121 in the absence of solvent under microwave irradiation. This reaction leads to polyfunctionalized 4-yliden-2-imidazolin-5-ones 122 (Scheme 9.36) [87]. 

The 3 + 2-cycloaddition of 1,2-dithiophthalides with nitrilimines yields benzo[c]thio-phenespirothiadiazoles regioselectively. The azomethineimines isoquinolinium-iV-aryllimide and A-(2-pyridyl)imide readily undergo 1,3-dipolar cycloaddition with electron-deficient dipolarophiles, dimethyl fumarate and dimethyl maleate, to yield tetrahydropyrazolo[5,l-a]isoquinolines in high yield. ° The 1,3-dipolar cycloadditions of electron-poor 1,3-dipoles, bicyclic azomethine ylides (27), with ( )-l-A,A-dimethylaminopropene to yield cycloadducts (28) and (29) are examples of non-stereospecific cycloadductions (Scheme 9). The synthesis of protected... 

The addition to alkenes normally leads to unstable adducts that lose carbon dioxide under the reaction conditions. The intramolecular cycloaddition of the sydnone (30) takes place at room temperature, however (Equation (5)) and the cycloadduct (31) has been characterized <86HCA927>. The unstable species formed by the loss of carbon dioxide are also azomethine ylides. It is therefore possible for a second 1,3-dipolar addition to take place, as illustrated in Scheme 6 for the reaction of 3-phenylsydnone with Al-phenylmaleimide <86TL317,92JA8414>. This 2 1 addition has been used as the basis of a synthesis of polyimides. Imides of the type (32) were used as the dipolarophiles and their reaction with 3-phenylsydnone gave linear polymers <87MM726>. 

The mechanism proposed involves desilyation of the silver complexed imidate and cycloaddition by the azomethine ylide 35 to give 37 followed by elimination (22). 

Imidate-derived dipoles have played a prominent role in the synthesis of the pyrrolizidine alkaloid retronecine (121).119 The imidate salt derived from lactam (118) was found to undergo a smooth desilylation reaction to produce azomethine ylide (119). Trapping of this dipole with methyl acrylate affords... 

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... 

Different approaches have been used to synthesize imidate- and thioimidate-derived azomethine ylids. 

Imidates, generated from secondary amides, are treated with trimethylsilyhnethyl triflate to give an azomethine ylid which reacts with electron-poor alkenes and acetylenes, yielding A2-pyrroline and pyrrole derivatives.54 Similar transformations are conducted from thioamides (vide infra). 

Like imidates, thioimidates were shown to be the precursors of azomethine ylids which lead to the formation of pyrroline and pyrrole derivatives through cycloaddition with dipolarophiles.454... 

This report covers two topics (1) The generation of 2-thioxo-2,4-dihydro-3fT-imidazol-l-ium-l-imides as intermediates in the course of [3+2] cycloaddition reactions of azoalkenes and thiocyanic acid resulting in the formation of l-aminoimidazole-2-thione derivatives some further reactions of these heterocycles are presented as well. (2) The rhodium-catalyzed intramolecular interaction of co-diazenyl a -diazo ketones giving rise to the formation of mostly two cyclic azomethine imine isomers with an exocyclic terminal nitrogen atom and with all three... 

Several methods for making pyrroles involve in situ generation of azomethine ylides and anions. In the presence of electrophilic acetylenes these can be trapped and converted to pyrroles. One source of azomethine ylides are A -(a-trimethylsilylmethyl) derivatives of imidates and thioimidates. Azomethine ylides are generated by desilylation with fluoride ion. The salts are obtained by N-alkylation of imidate esters <83TL4303> or S-alkylation of thioacetamides <86JOCi997>. The alkoxy or alkylthio groups are eliminated after cycloaddition. Electrophilic alkenes such as dimethyl maleate, dimethyl fumarate, maleonitrile and methyl acrylate give A -pyrrolenines (Scheme 80). 

Methoxy-substituted azomethine anions can also be generated by reaction of a-(tri- -butyl-stannyl)imidate esters, which undergo lithium-tin exchange on reaction with alkyllithium reagents. The adducts eliminate methanol, generating A -pyrrolenines (Equation (58)) <94TL264l>. 

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