Preparation and [2 + 3] cycloaddition of thienyl isocyanates with trimethylsilyl azide: one-pot synthesis of the thienyltetrazolin-5-ones

摘要: Efforts to prepare thienyl isocyanates by thermal reactions of thenoyl chlorides with trimethylsilyl azide (TMSA) led preferentially the formation 1,4-disubstituted tetrazolin-5-ones, arising interaction initially formed isocyanate TMSA. In fact, 2-thenoyl chloride and benzo[b]thiophene-2-carbonyl reacted 1 equiv. TMSA in refluxing carbon tetrachloride give 1-(2-thienyl or benzo[b]thienyl)-4-(2-thenoyl benzo[b]thiophenecarbonyl)tetrazolin-5-one 4d, e, whereas 3-thenoyl 1-(3-thienyl)-4-trimethylsilyltetrazolin-5-one adduct II which was converted, after hydrolytic desilylation, 1-(3-thienyl)tetrazolin-5(4H)-one 4c. Similar reactions, carried out more than two TMSA, all cases corresponding 1-heteroaryltetrazolin-5-one 4a–cvia silylated tetrazolin-5-ones II, at room temp, such gave essentially azides which, elimination excess were thermally converted 3 fairly good yields.