Synthesis of Five‐ and Six‐Membered Oxygen‐Containing Heterocycles via Intramolecular Cyclization Reactions of Arylalkyne‐Functionalized Electron‐Deficient Alkenes

ABSTRACT Intramolecular cyclization reactions of arylalkyne‐functionalized electron‐deficient alkenes to construct five‐ and six‐membered rings containing oxygen were investigated. Recently, we have found that the reaction of arylpropargyl amides of fumarate and ethenetricarboxylate by heating in DMSO gave aroyl‐substituted pyrrolidine derivatives as major products, probably via addition of water under metal‐free conditions. In this work, the reaction of arylpropargyl esters of ethenetricarboxylates at 80–110°C in DMSO gave aroyl‐substituted tetrahydrofuran derivatives in 33%–54% yield. On the other hand, thermal reaction of dimethyl 2‐(2‐(3‐phenylprop‐2‐ynyloxy)benzylidene)malonate in DMSO gave a complex mixture. Reaction of 2‐(3‐phenylprop‐2‐ynyloxy)benzaldehyde with Meldrum's acid under the Knoevenagel condensation conditions proceeded via arylalkyne‐functionalized electron‐deficient alkene intermediate to construct the multicyclic skeleton including pyran rings directly. The reaction mechanisms have been discussed using density functional theory (DFT) calculations.