Keteniminium Induced Dienone‐Phenol Rearrangement and Intramolecular 6‐endo‐dig Cyclization Cascade of Yne‐Dienone

Abstract

Dedicated to Prof. Peter Kündig for his 75th birthday Demonstrated herein is a keteniminium triggered dienone-phenol rearrangement of yne-dienone and a regioselective intramolecular 6-endo-dig cyclization of aryl-propargyl ether cascade for the synthesis of 2Hchromene bearing ketene-N,O-acetals. The gold-catalyst and ynamide combination forms a keteniminium species in situ and makes the dienone-phenol rearrangement viable with 1,2-migration of common alkyl substituents (methyl and ethyl) and phenyl group. The transformation tolerates common functional groups and N-sulfonyl protecting groups in ynamides exhibiting broad scope. The transformation proceeds through intramolecular proton transfer to the vinylic gold species; deuterium scrambling study supports this observation.

Advancements in Gold‐Catalyzed Cascade Reactions to Access Carbocycles and Heterocycles: An Overview

“…To synthesize the structurally challenging 2H‐chromene enabled ketene N,O ‐acetal derivatives, the Sahoo group demonstrated a keteniminium driven dienone‐phenol rearrangement and intramolecular 6‐endo‐dig cyclization cascade of yne‐dienone under Au‐catalysis (Scheme 28). [65] Yne‐dienone 75 and ynamides 11 underwent the cascade reaction in presence of 5 mol% JohnphosAuCl and 10 mol% AgNTf 2 in chloroform at 60 °C for 12 h to furnish the desired product 76 in 47–90% yield. Various aryl substituted ynamides gave good yield whereas aliphatic N‐protected ynamides delivered moderate yield.…”