General Synthesis of Polysubstituted Benzo[b]furans.
2-(Benzotriazol-1-ylmethyl)furans 4a-c, on treatment with n-BuLi followed by various alpha,beta-unsaturated ketones and aldehydes, gave the adducts 6a-f which underwent intramolecular cyclization to form substituted benzo[b]furans 10a-f. Lithiation and subsequent alkylation of 4a-c afforded intermediates 8a-c, which underwent similar transformations with alpha,beta-unsaturated ketones or aldehydes to give the corresponding polysubstituted benzo[b]furans 7a-c. o-Iodophenol (11) with 1-propargylbenzotriazole (1) in the presence of (PPh(3))(2)PdCl(2), CuI, and Et(3)N gave 2-(benzotriazol-1-ylmethyl)benzo[b]furan (12). The benzotriazolyl-CH(2) side chain of 12 was further elaborated by (i) alkylation with trans-cinnamaldehyde to give the adduct 14, followed by intramolecular cyclization to give dibenzofuran 17; (ii) alkylation with benzyl bromide followed by elimination or nucleophilic displacement of the benzotriazolyl moiety with Grignard reagent and subsequent dehydrogenation to give 2-alkenylbenzofurans 15 or 20, respectively; (iii) alkylation with (CH(3))(3)CCHO followed by low-valent titanium-promoted olefination to give olefin 19; and (iv) alkylation with benzaldehyde followed by Lewis acid catalyzed pinacol type reaction to give 18.
Katritzky
Alan R.
AR
Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200.
Fali
Clara N.
CN
Li
Jianqing
J