Au-catalyzed cascade addition/cyclization/H-transfer reactions of 3-(1-alkynyl)chromones to construct 4H-Furo[3,2-c]pyrans scaffold

Abstract

Using Au catalyst and ethyl Hantzsch ester as a hydrogen source, 3-(1-alkynyl)chromones were directly transformed to 4H-benzofuro[3,2-c]pyrans in good to excellent yields through a cascade process by addition, cyclization and hydrogen transfer under mild conditions.

AgSbF6‐Catalyzed Tandem Reaction of 2‐Alkynylanilines with Cyclic Enynones: Efficient access to 3‐Furo[3,2‐c]chromenylindoles and Related Scaffolds

“…On the other hand, enynones have been frequently used as versatile nucleophilic acceptors in the sequential conjugate‐addition reaction with different types of nucleophiles including H, alcohols, electron rich arenes, active methylene compounds, H 2 O etc followed by 5‐ endo‐dig oxacyclization promoted by several alkyne bond activating agents such as AuCl 3 ,– PtCl 2 , Cu I ‐salts,– AuCl/AgOTf, Ph 3 PAuOTf, CuI‐Pd(OAc) 2 , I 2 . This novel procedure leads to an excellent atom‐economical route to highly‐substituted furan derivatives as this core moiety constitutes many natural products, pharmaceuticals and agrochemicals…”

DMAP-Catalyzed Annulation Approach for Modular Assembly of Furan-Fused Chromenes

“…Recently, transition-metal-catalyzed strategies have emerged targeting arene-substituted furo­[3,2- c ]­chromenes (Scheme b). By employing alkynylchromone as the key starting material, Larock and Hu have independently developed gold-catalyzed reaction systems for constructing furo­[3,2- c ]­chromenes. Ma has disclosed a Rh-catalyzed two-step process by using diazochromanone and alkynes as starting material …”

One-Pot Novel Regioselective Cycloisomerization Synthesis of 2-Substituted or 3-Substituted 4H-Furo[3,2-c]chromene through the Intermediate Cyclopropenes of 3-Diazochroman-4-one and Phenylacetylene

“…The 4 H -furo[3,2- c ]chromene skeleton can be found in many natural products and exhibits potential biological activity. Most synthetic methods have focused on the construction of a pterocarpan system which is the combination of benzofuran and chromene scaffold. − Herein, we report the synthesis of unique cyclopropenes containing a chroman-4-one motif using 3-diazochroman-4-one and phenylacetylene with rhodium(II) catalyst, followed by regioselectively cycloisomerization to give 2-substituted or 3-substituted 4 H -furo[3,2- c ]chromene, respectively. Using BF 3 ·Et 2 O as catalyst, 2-substituted 4 H -furo[3,2- c ]chromene was exclusively obtained.…”