1.3- Dipolar cycloaddition reactions cyano group

Carbonyl or cyano groups, of proven value in Diels-Alder reactions and 1,3-dipolar cycloadditions, are unsuitable for anionic cycloadditions owing to the pronounced nucleophilic and basic character of the anionic reagents. Instead of cycloaddition nucleophilic attack of these groups or deprotonation of the substrates would occur. This means that aromatic residues are indispensible which are practically unremovable after the cycloaddition and, unlike the carbonyl group, hardly unsuitable for subsequent synthetic steps. 

Reactions between 5-cyanotetrazole and transition metals, when performed in boiling acetone, lead to hydrolysis of the cyano group and formation of 5-carbamyl tetrazolate complexes (68). Complexes containing 1- or 5-substituted tetrazolate anions can also be obtained by 1,3-dipolar cycloaddition of organic isonitriles (RNC) (15) or nitriles (RCN) (61), respectively, to coordinated azide ligands [Eqs. (3) and (4)]. 

The Knoevenagel condensation was followed by a 1,3-dipolar cycloaddition of sodium azide with one of the cyano groups to afford the tetrazoles 228 and 230 in moderate to good yields. The reactions were conducted in aqueous solution at elevated temperatures and were mostly finished within one day of reaction time. 

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