Organocatalytic ( Z / E )-Selective Synthesis of 3-Vinylnaphthofurans via a Formal (3 + 2) Cycloaddition.

A formal (3 + 2) cycloaddition of 1,4-enediones with 2-naphthols was established under the catalysis of trifluoromethanesulfonic acid as an organocatalyst, leading to the efficient synthesis of structurally diverse 3-vinylnaphthofurans with high yields and excellent ( Z / E )-selectivities (up to 96% yield, all >20:1 Z / E ). This formal (3 + 2) cycloaddition involved a cascade reaction process, and the intramolecular hydrogen bond in the structure of 3-vinylnaphthofurans should play an important role in controlling the ( Z / E )-selectivity of the newly formed vinyl group. Moreover, this class of 3-vinylnaphthofurans was discovered to have an axial chirality. This work provides an organocatalytic approach for constructing multi-substituted vinylnaphthofurans via a cascade reaction with excellent control of the ( Z / E )-selectivity, which will serve as a useful strategy for synthesizing vinylnaphthofurans via in situ construction of the furan core and formation of the vinyl group.