Azirines vinyl substituted

Whereas the cycloaddition of arylazirines with simple alkenes produces A -pyrrolines, a rearranged isomer can be formed when the alkene and the azirine moieties are suitably arranged in the same molecule. This type of intramolecular photocycloaddition was first detected using 2-vinyl-substituted azirines (75JA4682). Irradiation of azirine (54) in benzene afforded a 2,3-disubstituted pyrrole (55), while thermolysis gave a 2,5-disubstituted pyrrole (56). Photolysis of azirine (57) proceeded similarly and gave 1,2-diphenylimidazole (58) as the exclusive photoproduct. This stands in marked contrast to the thermal reaction of (57) which afforded 1,3-diphenylpyrazole (59) as the only product. 

Whereas the cycloaddition of arylazirines with simple alkenes produces d -pyrrolines, a rearranged isomer (i.e., 29) can be formed when the alkene and the 2H-azirine moieties are suitably arranged in the same molecule. This type of intramolecular photocycloaddition was first detected using 2-vinyl-substituted 2H-azirines (75JA4682). 

A typical high-yield synthesis of a vinyl substituted 2/f-azirine is shown by the conversion of the azide 624 into 625". Similar behaviour is seen for the isomeric azidoeneynes 626 and 627 that are converted into the alkynyl substituted azirine 628 while irradiation of the azidoallylphosphonates 629 yields the corresponding azirines 630 and 631 is transformed into 632 at 0 This route to azirines has been extended to the synthesis of the bis-2/f-azirines 633 and 634, which are formed by irradiation of the bis azides 635 and 636", respectively. The formation of these products arises by sequential loss of nitrogen. Thus the bis azide 635 is converted to 637 prior to the ultimate formation of the final product 633. Methylene azirines such as 638 are formed on photoelimination of nitrogen from the azides 639. In this instance, however, the presence of the azirine derivative was established by trapping experiments with HCN when the adducts 640 are formed . 

IV. INTRAMOLECULAR L5 ELECTROCYCLIZATION REACTIONS OF VINYL-SUBSTITUTED IH-AZIRINES... 

Analogous results were secured in the thermal ring-opening reaction of the corresponding diphenyl-substituted azirine 346/ 2-Vinyl-substituted 2H-azirines have also been suggested as intermediates in the thermolysis of a number of substituted butadienyl azide systems. ... 

Further examples which illustrate the generality of the thermally induced intramolecular cyclization of 2/f-azirines have been reported. When the conjugation in the 2-position was extended (348), two possible products can be formed. In fact, however, only the 2-vinyl-substituted pyrrole 349 was detected in the reaction mixture. ... 

The condensation of amines with 2-formyl-3-phenyl-2/f-azirine (350) yields the imines 352, which undergo thermal reorganization to pyrazoles 353 via 1,5-dipolar cyclization of the resulting vinylnitrene intermediate derived from CN bond rupture. The thermal reactivity of 350 and 352 parallels completely that of the 2-vinyl-substituted 2/f-azirines. 

Photogenerated nitrenes can undergo cycloaddition with alkenes intermolecular reaction leads to aziridine products (5.38), and intramolecular reaction in vinyl azides gives azirines (5.39). The bicyclic azirine from phenyl azide has not been isolated, but it is the intermediate that best accounts for the formation of a substituted azepine when this azide is irradiated in the presence of a secondary amine (5.401. 

One of the best known reactions of 1-azirines is the acid/catalyzed hydrolysis to aminoketones. Since the Neber reaction also accomplishes this same synthetic end, this reaction may appear to have little practical value. This is not the situation because with the Neber reaction there is no control over the aminoketone that will be obtained from a given ketone. For example, when oxime (127) derived from benzyl methyl ketone (126) is subjected to the Neber reaction aminoketone 128 is obtained.59 The amino function is substituted for the most acidic a-hydrogen. The isomeric aminoketone (132) that could not be prepared by the Neber reaction can be formed by the hydrolysis of 1-azirine (131). The synthesis of this 1-azirine has been accomplished from allyl benzene (129) through vinyl azide (130) using iodine azide.22... 

The simplest member of the class of vinyl azides, H2C=CH-N3, has been known for about 100 years. However, it was not until the late 1960s that vinyl azides became an important and synthetically useful class of organic compound. The most interesting and important reaction of vinyl azides is the formation of azirines produced upon photolysis and thermolysis of vinyl azides. Smolinsky and Pryde first observed azirine formation, together with a small amount of keteneimine, by gas-phase pyrolysis of a-aryl-substituted vinyl azides. 

Hassner and Fowler first discovered that several a-substituted (R H) vinyl azides produce 2-mono- or 2,3-disub-stituted-l-azirines in high chemical yield (80 to 90%) upon photolysis. 

I Q I 3-Substituted 2H-azirines 8 are prepared by thermolysis or photolysis of vinyl azides... 

As indicated in Table 6.1 some 2/f-aziiines are isolated from one-pot reactions in which the vinyl azide precursors are produced in situ. For example, 3-dialkylamino-2//-azirines 4 have been prepared from tertiary amides 3 the vinyl azide intermediates are generated by successive chlorination and reaction with sodium azide (Scheme 6.2). The conversion of these vinyl azides into azirines takes place at room temperature and it is clear that the nature of the substituents on the double bond of vinyl azides influences their temperature of decomposition. Fluoro substituted vinyl azides also decompose at room temperature. ... 

The photolysis of the halo substituted vinyl azides 18 produced the azirines 19 these were then thermally isomerized to the more stable 2//-azirines 20 (Scheme 6.9). This type of isomerization has also been observed with fluoro substituted azirines. ... 

Smolinsky and Pryde first observed azirine formation, together with small amount of ketenimin, by gas-phase pyrolysis of a-aryl substituted vinyl azides. 

Apparently, 0-vinyl oxime is deprotonated under the action of the superbase forming carbanion L that further substitutes intramolecularly the vinyloxy anion to close the azirine cycle ring M (Scheme 1.167). Its hydration into hydroxyaziridine N followed by a rearrangement results in N-benzylbenzamide. 

Like the pyrrole synthesis, the assembly of 4-methylene-3-oxa-l-azabicyclo[3.1.0]hexanes is likely triggered by the formation of O-vinyl oxime (detected by GLC and NMR). The deprotonation of O-vinyl oxime in a-position relative to the oxime function and the further intermolecular nucleophilic substitution of the vinyloxy group can lead to azirine A (Scheme 1.178). The latter reacts with acetylene (in the form of carbanion) to give acetylenic ethynyl aziri-dine B (the nitrogen analog of the Favorsky reaction), which is added to the third... 

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