Efficient Syntheses of 2-Functionalized Thiophenes, Cyclopent[b]thiophenes, and Polysubstituted Benzo[b]thiophenes from 2-(Benzotriazol-1-ylmethyl)thiophenes
摘要:
Diverse 2-(functionalized-alkyl)- and 2-alkenylthiophenes 2a,b, 4a,b, and 6a-d are prepared via the side chain elaboration of 2-(benzotriazol-1-ylmethyl)thiophenes 3a,b, themselves readily available from the condensation of 1-(hydroxymethyl)benzotriazole with thiophenes 1a,b. Treatment of 2-(benzotriazol-1-ylmethyl)thiophenes 3b and 5gj with styrenes in the presence of zinc bromide results in formal [3 + 2] cycloaddition to give in good yields substituted cyclopent[b]thiophenes 16a/17a, 16b/17b, and 18. Lithiation and 1,4-addition to a variety of alpha,beta-unsaturated ketones and aldehydes, and subsequent acid-catalyzed intramolecular cyclization followed by debenzotriazolylation-dehydration converts 3 and 5 to a range of polysubstituted benzo[b]thiophenes 19a-d and 25a-e in moderate to excellent yields. NOE difference spectroscopy and NMR H-1-C-13 long-range correlation support structures of types 19 and 25 and exclude those of type 26, thus confirming the cyclization pathway.
The heterocyclic ionic liquid-catalyzed direct oxidative amination of benzylic sp3 C–H bonds via intermolecular sp3 C–N bond formation for the synthesis of N-alkylated azoles under metal-free conditions is reported for the first time. The catalyst 1-butylpyridinium iodide can be recycled and reused with similar efficacies for at least eight cycles.
Efficient Syntheses of 2-Functionalized Thiophenes, Cyclopent[<i>b</i>]thiophenes, and Polysubstituted Benzo[<i>b</i>]thiophenes from 2-(Benzotriazol-1-ylmethyl)thiophenes
作者:Alan R. Katritzky、Larisa Serdyuk、Linghong Xie、Ion Ghiviriga
DOI:10.1021/jo970672g
日期:1997.9.1
Diverse 2-(functionalized-alkyl)- and 2-alkenylthiophenes 2a,b, 4a,b, and 6a-d are prepared via the side chain elaboration of 2-(benzotriazol-1-ylmethyl)thiophenes 3a,b, themselves readily available from the condensation of 1-(hydroxymethyl)benzotriazole with thiophenes 1a,b. Treatment of 2-(benzotriazol-1-ylmethyl)thiophenes 3b and 5gj with styrenes in the presence of zinc bromide results in formal [3 + 2] cycloaddition to give in good yields substituted cyclopent[b]thiophenes 16a/17a, 16b/17b, and 18. Lithiation and 1,4-addition to a variety of alpha,beta-unsaturated ketones and aldehydes, and subsequent acid-catalyzed intramolecular cyclization followed by debenzotriazolylation-dehydration converts 3 and 5 to a range of polysubstituted benzo[b]thiophenes 19a-d and 25a-e in moderate to excellent yields. NOE difference spectroscopy and NMR H-1-C-13 long-range correlation support structures of types 19 and 25 and exclude those of type 26, thus confirming the cyclization pathway.