Direct Oxidative Cyclization Of 3-arylpropionic Acids Using Pifa Or Oxone:synthesis Of 3,4-dihydrocoumarins

Coumarin and its derivatives are one of the most privileged structural motifs frequently found in natural products and pharmaceuticals.As an important class of coumarins, 3,4-dihydrocoumarins are widely distributed in nature and exhibit some interesting biological activities, such as anti-herpetic, anti-inflammatory,anti-oxidative, anti-aging, and anti-cancer activities,Therefore, development of efficient methods for the synthesis of dihydrocoumarins have attracted great interest in recent years. However, many of these methods suffer disadvantages from using a large excess of expensive transition-metals and harsh conditions. To achieve the environmental demands for'green'chemical procedures, we were prompted to explore the feasibility of dihydrocoumarin synthesis by transition-metal-free oxidative C-O formation reaction from the corresponding carboxylic acidsRecently, utilization of hypervalent iodine compounds anoxone in oxidative reactions has received great attention for their low toxicity compared with heavy metal oxidants, mild reaction conditions,special reactivity, and easy handling. We envisioned that oxidation of 3-arylylpropionic acids with hypervalent iodine reagents or oxone would generate radical cation intermediates,which could be attacked by carboxylic acid moiety to provide bicyclolactones. In this thesis, we disclose our investigation for the oxidative cyclization of 3-arylpropionic acids to 3,4-dihydrocoumarins using hypervalent iodine reagents or oxone as oxidants.We developed a novel method for the synthesis of 3,4-dihydrocoumarin through direct oxidative cyclization of 3-arylpropionic acids using PIFA or Oxone as an oxidant. The synthetic utility of these reactions is enhanced by using Oxone as an inexpensive,safe, and environmentally benign oxidant.