Synthesis of multisubstituted furans via copper-catalyzed intramolecular O-vinylation of ketones with vinyl bromides

Vilsmeier-Haack-Initiated Formylative Rearrangement of Spirodioxo-lan-5-ones into Functionalized 4,5,6,7-Tetrahydrobenzofurans

Pharmaceutically relevant bicyclic furans can be synthesized in a single step from substituted dioxolan-5-ones by reacting with Vilsmeier-Haack reagents. These reagents are generated from POCl3 or PBr3 and DMF. The reaction cascade is mechanistically complex and involves deoxyhalogenation, iminomethylation, and electrophilic rearrangement steps, which are facilitated by the DMF solvent. The synthesis of hard-to-access 4,5,6,7-tetrahydrobenzofurans and substituted aliphatic furans is particularly useful. These compounds are potential isosteres of 2,3-dihydrobenzofuran pharmacophores and could be of interest for drug discovery.

Flexible Approach for the Synthesis of Annulated 4H-Pyrans Based on a Cu(I)-Catalyzed C-Allylation/O-Vinylation Reaction of Cyclic 1-Bromoallyl Tosylates with Cyclic and Acyclic 1,3-Dicarbonyls

The Cu(I)-catalyzed reaction between five-, six-, seven-, and eight-membered cyclic 1-bromoallyl tosylates and five- and six-membered cyclic 1,3-dicarbonyls in DMF at 80 °C using Cs₂CO₃ as a base and 2-picolinic acid as an additive selectively delivers a wide array of bisannulated 4H-pyrans in a single step with yields up to 92%. The transformations are considered to proceed as intermolecular C-allylations/intramolecular O-vinylations. With six-membered cyclic 1-bromoallyl tosylates and acyclic β-ketoesters as substrates, the corresponding 5,6,7,8-tetrahydro-4H-chromene-3-carboxylates are obtained with yields up to 59%.

Selective synthesis of 2,5-disubstituted furan-3-carboxylates and the isomeric 2,4-disubstituted furan-3-carboxylates

Regioselective formation of 2,5-disubstituted furan-3-carboxylates and the isomeric 2,4-disubstituted furan-3-carboxylates from the same substrates was realized under different reaction condition.