Ring-opening azidation

A series of 5-aminoaryltetrazoles were obtained directly from the corresponding l-aryl-5-aminotetrazoles by a one-pot sequential ring-opening, azidation, and intramolecular cyclization. 5-Alkylamino-l-aryltetrazoles are formed by a similar mechanism from 1,4-disubstituted tetrazolium salts. The influence of the aryl substituents and reaction conditions on the regioselectivity of the intramolecular cyclization of the intermediate guanyl azides was revealed <2006S1307>. 

Attempts to apply the azide-tetrazole isomerism to the synthesis of tetrazolo[l,5-a][l,3,5]triazines were published <88IZV491>. This equilibrium was found to be shifted generally to the ring opened azides (31), and the maximum amount of the tetrazole (32) of 15% was detected in DMSO-de at 20 °C in the case of = H, R = morpholino group. The same tetrazolo ring system was, however, found to be stable with 5-styryl and 7-thio substitution <87LA65> aminotetrazole (33) when reacted with cinnamoyl isothiocyanate alTorded the tetrazolotriazine-thione (34) most likely formed via cyclization of the intermediate thiourea. 

Nucleophilic ring opening of epoxides by ammonia (Section 16 12) The strained ring of an epoxide is opened on nucleo philic attack by ammonia and amines to give 3 ammo alcohols Azide ion also re acts with epoxides the products are p azido alcohols... 

CPB1457), whilst with azide ion the chloro compound (107) underwent ring opening and reclosure to give the 2-tetrazolyl-3-aminopyridine (108) (74CR(C)(278)l42l). 

Apparent nucleophilic attack on large, fully unsaturated rings may occur by way of attack on a valence tautomer, such as the reaction of oxepin with azide ion. Attack on the oxanorcaradiene valence tautomer leads to ring opening of the three-membered ring, and formation of 5-azido-6-hydroxy-l,3-cyclohexadiene (Section 5.17.2.2.4). 

Arylsulfenyl azides in this reaction mainly give the product of the triazole ring opening 380, which is isomeric to the expected triazole 381 detected only in negligible quantities (72S571). 

Scheme 2.13 Synthesis of vinylaziridines through sodium azide-mediated ring-opening of alkenylepoxides.

The ring-opening reactions of aziridines 16 with amines deserve special attention. Unlike ring-openings with the other nucleophiles examined, they do not require added base, and they do not produce stoichiometric byproducts (as with azide). In certain cases, they do not even require a solvent, as exemplified by the ring-opening of aziridine 18 (Table 12.12, entries 1-3). In addition, the reactions... 

The ring-opening process leading to 164 (route a) is analogous to that which has been demonstrated to follow the cycloadditions of tosyl azide to certain enamines176. Similar results have been reported for the reaction of 2,3-diphenylcyclopropenone with 2-diazopropane177. Other 1,3-dipolar cycloadditions with thiirene dioxides could also be affected (see below). 

Watt and coworkers139 prepared the a-azidoaldehydes (242) by nucleophilic ring opening with sulfinate ion expulsion of a, /(-epoxy sulfones 241 with sodium azide in DMF... 

It may be concluded that the conversion of functionalized oxiranes into the corresponding aziridines by an azide ring opening followed by a Staudinger ring closure with triphenylphosphine constitutes a general method for the preparation of aziridines with high enantiopurity. 

The analogous chromium complex was used in the asymmetric ring opening of meso epoxides with trimethylsilyl azide [15] (Scheme 4). In this case a strong dependence on the anion of the ionic hquid was observed. Anions leading to hydrophobic ionic hquids, such as PFe" and SbFe", led to high... 

Method B was also used in the preparation of occluded (salen)Cr complexes. ligands Ih and li were prepared within the pores of Cr -exchanged EMT and Y zeolites, respectively [25]. These complexes were tested as catalysts in the ring opening of meso-epoxides with trimethylsilyl azide (Scheme 4). The occluded complexes showed a dramatic decrease in catalytic... 

The same salts can be used to catalyze ring opening by other nucleophiles such as azide ion121 and cyanide ion.122... 

The activation of an anomeric hydroxyl group from partially protected or unprotected monosaccharides can be achieved via 1,2-cyclic sulfite formation. A subsequent trans-ring opening with azide N3 affords one anomeric derivative exclusively 133... 

Table 14 Ring openings of 5-thia-1 -thioniabicyclo[4.3.0]nonane salt 91 with sodium azide (Equation 25)...

Sulfonium salt 103a also underwent ring-opening reactions with nucleophiles, such as NaBH4, sodium azide, and sodium methanethiolate, to afford trithiocins 107 (see Equation (30) and Table 18) <1996BCJ2349> and <1998BCJ1187>. 

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