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Phosphine vs DBU-Catalyzed Annulation Reactions of β'-Acetoxy Allenoates with Acyl-Tethered Benzothiazole
Sachin Chauhan1, K C Kumara Swamy1
1School of Chemistry, University of Hyderabad, Hyderabad 500046, Telangana, India.
Abstract:
Dearomative annulation reaction of acyl-tethered benzothiazole bisnucleophiles with β'-acetoxy allenoates by switching the Lewis base is developed. The DBU-catalyzed reaction gives benzothiazole-fused 1,4-dihydropyridine carboxylates by (3 + 3) annulation chemoselectively. By contrast, the PR3-catalyzed reaction gives benzothiazole-fused azepines by (4 + 3) annulation and cyclopentene carboxylates by (4 + 1) annulation; the ratio of the latter two products depends on the solvent. A possible rationale for the difference in the reactivity, based on the 1,4/1,5-addition of the 2-acyl-tethered benzothiazole to the key phosphonium intermediate, is provided.
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