1.2.4- Oxadiazoles forming tetrazoles

The energetic 1,3,4-oxadiazole (22) is synthesized from the reaction of the tetrazole (20) with oxalyl chloride. In this reaction the tetrazole (20) undergoes a reverse cycloaddition with the expulsion of nitrogen and the formation of the 1,3-dipolar diazoalkane (21) which reacts with the carbonyl groups of oxalyl chloride to form the 1,3,4-oxadiazole rings. 

Tetrazoles (130) and nitrile oxides form mixtures of isomers (131) and (132) (Scheme 59). While thermolysis of (132) (R H) gives 1,2,4-oxadiazoles (134) via azides (133) almost quantitatively, compounds (131) decompose to mixtures of products (Scheme 59) <87BSB675>. 

Acylation with the acylium ion in the gas phase. An unusual experiment was performed by Seldes et aL <20010MS1069>. The N2-tautomeric form of a 5-substituted tetrazole was reacted in the gas phase with an acyl ion generated as the secondary reactive chemical by ionization plasma in a mass spectrometer. It was suggested that the mechanism of this process involved the formation of an acylated tetrazole intermediate, which could not be isolated in a condensed phase, and by rearrangement with nitrogen loss afforded an oxadiazole <20010MS1069> (cf. Section 6.07.5.2.2, Equation 16). This experiment has no preparative value but provides important information on the interaction mechanism between the neutral N-unsubstituted tetrazoles and electrophilic agents in the gas phase. 

The rearrangement of l-aryl-5-aminotetrazoles by the action of acetic anhydride to 2-arylamino-5-methyl-l,3,4-oxadiazoles or to their acetyl derivatives has been known for some time.101,102 This reaction may be widely generalized. The action of aromatic and aliphatic acid anhydrides and acid chlorides on 5-alkyl(aryl)tetrazoles produces 1,3,4-oxadiazoles in excellent yield. iV-Acyl tetr azoles (31) are formed as intermediates. These are converted with elimination of... 

The reaction of 5-aryl (hetaryl)tetrazoles (Li) with phenyl isocyanate under the conditions of microwave activation formed the corresponding 2-anilino-5-aryl(hetaryl)-l,3,4-oxadiazoles (Lii) in high yields [43]. 

Oxadiazoles are formed on heating tetrazoles with acylating agents, via rearrangement of first-formed 2-acyl derivatives. ... 

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