Synthesis of Polysubstituted Naphthofurans and Indenofurans Based on a Regiodivergent Intramolecular Carbometalation Strategy with 2-(2'-Alkynylaryl)-3-iodofurans.

Efficient methods for the synthesis of two types of furan-fused tricyclic compounds were developed based on a regiodivergent intramolecular carbometalation strategy using 2-(2'-alkynylaryl)-3-iodofurans as a common substrate. The iodine-magnesium exchange/copper-mediated 6-endo-anti intramolecular carbometalation sequence followed by nucleophilic substitution or palladium-catalyzed cross-coupling provided 2,3,4,5-tetrasubstituted naphtho[1,2-b]furans. On the other hand, the formal intramolecular 5-exo-anti carbopalladation/cross-coupling sequence afforded 2,3-disubstituted 4-alkylidene-4H-indeno[1,2-b]furans. The present methods provide new access to a wide range of well-organized polysubstituted naphtho[1,2-b]furans and indeno[1,2-b]furans in a positional selective manner that are otherwise difficult to access.