Application of Benzofuran-Derived Azadienes as Two-Carbon Building Blocks in Annulations: Chemo- and Diastereoselective Construction of Spiro-Benzofuran Scaffolds

A base-promoted (2+4) annulation of benzofuran-derived azadienes withpara-quinone methide derivatives has been established, which afforded spiro-benzofuran derivatives in generally high yields (57-97%) and with good diastereoselectivities (85:15 to >95:5 dr). This reaction not only represents the first application of benzofuran-derived azadienes as two-carbon building blocks in annulations, but also provides an efficient protocol for the construction of spiro-benzofuran scaffolds with chemoselectivity and high diastereoselectivity. This approach will enrich the chemistry of benzofuran-derived azadiene-involved reactions.