Aziridines thermolysis

Acromelic acid A (260), isolated from Clitocybe acromelaga, displays the most potent polarizing effect of aU known kainoids. By application of the same intramolecular aziridine thermolysis route described above, Takano et al. (80) outlined a concise entry into such compounds. Thermolysis of the chiral aziridine 261, derived from (5)-0-benzylglycidol in 1,2-dichlorobenzene at 200 °C, furnished the single reaction product 262 in 73% yield. The complete control over the... 

A comparison of methods to generate azomethine ylides via 4-oxazohne ring opening vs. aziridine thermolysis has shown that the oxazoline method can produce the same azomethine dipole under kinetic control as the aziridine method under thermodynamic... 

Thermolysis of the aziridine (446) in the presence of diphenylketene gave a mixture of the pyrrolidone (447 minor product) and the oxazolidine (448 major product). In this instance the preferential addition to the C=0 bond is explained in terms of steric effects (72CC199). Similar addition to diphenylacetaldehyde takes place with the same orientation and the oxazolidine (448a) was obtained. When the reaction of the aziridine with the aldehyde was carried out in the presence of hydrogen selenide a selenazolidine was obtained (72BSB295). 

Finally, one last system worthy of mention involves the thermolysis of aziridine (286) in refluxing benzene to generate phthalimidonitrene (287) whieh ean be trapped in the usual way (72CC884). 

Aziridine, alkylidene-N-ethoxycarbonyl thermolysis, 7, 78 Aziridine, /V-amino-... 

Aziridine, cis-7V-t-butyl-3-ethynyl-2-vinyl-rearrangement, 7, 540 Aziridine, 2-chlorocarbonyl-ring expansion, 7, 42 Aziridine, 2-chloromethyl-synthesis, 7, 42 Aziridine, Mcyanodiphenyl-irradiation, 7, 61 Aziridine, dihalo-reduction, 7, 74 thermolysis, 7, 73... 

Thermolysis of the azide 15, bearing an allyl side chain, is more complex, and in addition to ethyl 4-allylindole-2-carboxylate and ethyl 4-methyl-l//-3-benzazepine-2-carboxylate (16 oil), two unstable tricyclic aziridines 17 and 18 are produced.82 A mechanistic rationale for these results has been suggested. 

Thermal rearrangement of 2-vinylaziridine 203, with an electron-withdrawing substituent on the nitrogen atom, at reflux in decalin predominantly yielded 2-pyr-roline 204 along with some 3-pyrroline derivatives 205 (Scheme 2.50) [79]. A similar reaction was also observed with l-alkyl-2-phenyl-3-vinylaziridines 206 [80]. From these observations, the nature of the products formed depends on the natures of the substituents on the aziridine ring if the ring carbon carries a phenyl substituent, the thermolysis in most cases preferentially yields 2-pyrrolines. 

Thermolysis of acyl azides and subsequent cyclization to give aziridines has been reported by Egli and Dreiding [39]. Heating of acylazide 34 (Scheme 3.11) in an autoclave afforded aziridine 35 in 74% yield [39]. 

Aziridines can be prepared directly from double-bond compounds by photolysis or thermolysis of a mixture of the substrate and an azide. The reaction has been carried out with R = aryl, cyano, EtOOC, and RSO2, as well as other groups. The reaction can take place by at least two pathways. In one, the azide is converted to a nitrene, which adds to the double bond in a manner analogous to that of carbene addition (15-62). Reaction of NsONHC02Et/ CuO [Ns = A(/7-toluenesulfonyl-inimo)] and a conjugated ketone, for example, leads to the A-carboethoxy aziridine derivative.Calcium oxide has also been used to generate the nitrene.Other specialized reagents have also been used." ... 

The overall pathway for the conversion of the unsaturated azido ether 281 to 2,5-dihydrooxazoles 282 involves first formation of the dipolar cycloaddition product 287, which thermolyzes to oxazoline 282 or is converted by silica gel to oxazolinoaziridine 288. While thermolysis or acid-catalyzed decomposition of triazolines to a mixture of imine and aziridine is well-documented [71,73], this chemoselective decomposition, depending on whether thermolysis or exposure to silica gel is used, is unprecedented. It is postulated that acidic surface sites on silica catalyze the triazoline decomposition via an intermediate resembling 289, which prefers to close to an aziridine 288. On the other hand, thermolysis of 287 may proceed via 290 (or the corresponding diradical) in which hydrogen migration is favored over ring closure. 

Aziridines are important compounds due to their versatility as synthetic intermediates. In addition, aziridine rings are present in innumerable natural products and biologically active compounds. Nitrene addition to alkenes is one of the most well established methods for the synthesis of aziridines. Photolysis or thermolysis of azides are good ways to generate nitrenes. Nitrenes can also be prepared in situ from iodosobenzene diacetate and sulfonamides or the ethoxycarbonylnitrene from the A-sulfonyloxy precursor. 

Photolysis of ferrocenylsulphonyl azide in cyclohexene gave the corresponding aziridine derivative (9%), but thermolysis did not 17>. This could be an addition of the triplet nitrene to the olefin and studies on the stereospecificity of this reaction are under way. 

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... 

Thermolysis of the pentacoordinate 1,2-thiazetidine 1-oxide 56, which was synthesized for the first time and characterized by X-ray crystallographic analysis, gave the corresponding aziridine 57 and a cyclic sulfinate almost quantitatively <06OL4625>. 

---