Azides cyclizations

The course of the photochemically mediated isomerization of vinylazirines is dependent on the stereochemistry of the vinyl group, as is illustrated in Scheme 94a (75JA4682). Under thermal conditions the isomerization proceeds through formation of the butadienylnitrene and subsequent pyrrole formation. Analogous conversions of azirines to indoles have also been effected (Scheme 94b). It is possible that some of the vinyl azide cyclizations discussed in Section 3.03.2.1 proceed via the azirine indeed, such an intermediate has been observed... 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cyclized rubber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenolic structure renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxylic acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubility is controlled by chemical and polarity differences rather than molecular size. 

Kozikowski et al. have described a synthesis of clavicipitic acids where a key step involved preparation of the imine (202).112 Azide cyclization at 190 C presumably afforded a triazoline which, however, was nonisolable affording (202) in 62% yield. 

Oxidative cyclizations of 3-(/ -azidoethyl)indoles with BTIB afford pyr-roloiminoquinones 15, compounds that appear as sub-structures in biologically active marine alkaloids such as the makaluvamines and discorhabdins (Scheme 22) [67- 69]. In fact, BTIB-mediated sulfide and azide cyclizations, and a-azido-nation of the cyclic sulfide with PhIO/TMSN3, were incorporated into the first total synthesis of ( )-makaluvamine F [68,69]. 

The j8-azidoacrylester 31 was obtained by a corresponding reaction sequence and also on direct treatment of the phosphorane with acetyl azide. Unfortunately, a number of other phosphoranes treated with either acetyl azide or acetyl chloride and sodium azide cyclized to 4-,5-iV-acetyl-l, 2,3-triazoles... 

Conjugated dienyl azides cyclize to 2//-azirines, and these isomerize to 2//-pyrroles at higher temperatures. Thus, the stable 2,2-dicyano-2//-pyrrole 12 was formed in a two-stage thermolysis of the azide 11 (Eq. 8).30 High yields (82-87%) of 2//-pyrroles 14 and 16 were obtained by thermal cycliza-tion of the corresponding vinyl azides (e.g, 13).31 The 2//-azirine 15 was... 

All attempts to generate 3-alkoxy- or 3-aryloxy-, 3-amino-, and 3-chloro-anthranils by thermolysis of o-azidoesters,169,170 184,193 -amides,194 and acid chlorides,194 have so far failed. Dyall attributes (in part) the failure of o-azidoesters to yield 3-alkoxyanthranils to the enhanced resonance stabilization of the ester carbonyl relative to the ketone group.184 However, in the p-benzoquinone series thermal azide cyclizations onto an adjacent ester grouping are well established e.g., 142 -> 143.172,195 In fact, the diazido-p-benzoquinone diester 144 decomposes in boiling benzene to give the benzo[l, 2-c 4,5-c ]diisoxazole-4,8-dione 145 in 83% yield.196... 

Treatment of the sulfonylcarbodiimides 152 with hydrazoic acid yielded the 1-substituted 5-sulfonylaminotetrazoles (153) via an imino azide [Eq. (23)].373 In general, such azides cyclize onto the nitrogen bearing the more electron-donating substituent (see Section IV). Compounds... 

The formation of an azepine ring by means of an intramolecular azide cyclization has often provided the key step in the synthesis of clavicipitic acid (126) <84JOC23io> (Scheme 19). 

Phenolic resin has been used to replace bis-azide-cyclized polyisoprene through the incorporation of a variety of azides, giving a negative resist that is sensitive to broad areas of visible and UV light. A monoazide in-... 

Scheme 7.49 Synthesis of quinoxaline derivatives via tandem oxidative azidation/cyclization...

Ma H, Li D, Yu W (2016) Synthesis of quinoxaline derivatives via tandem oxidative azidation/cyclization reaction of N-arylenamines. Org Lett 18(4) 868-871... 

In our approach to the synthesis of amphorogynine C, we used the Claisen rearrangement product 10 as a starting material and an intramolecular olefin-azide cyclization as a key step. The retrosynthetic analysis is shown in Figure 14.9. The... 

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