Palladium-Catalyzed Annulation of Aryl-1,2-diols and Propargylic Carbonates. Theoretical Study of the Observed Regioselectivities

✍ Scribed by Jean-Robert Labrosse; Paul Lhoste; Françoise Delbecq; Denis Sinou

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 201 KB
• Volume: 2003
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/ejoc.200300071

✦ Synopsis

Abstract

Methyl 1‐methylprop‐2‐ynyl carbonate reacts with 3‐ and 4‐substituted benzene‐1,2‐diols to give 2,3‐dihydro‐3‐methyl‐2‐methylidene‐1,4‐benzodioxines, as a mixture of regioisomers in the case of methoxy‐substituted diphenol, and a single regioisomer for the nitro‐ and the formyl‐substituted diphenols. The oxyanion which attacks first corresponds to the less acidic hydroxy function, and the attack of the second oxyanion on the η^3^‐allylpalladium intermediate is directed toward the more substituted carbon atom. In order to explain the regioselectivity of the cyclization, a theoretical study based on density functional theory (DFT) has been performed. The first step implies an equilibrium between the two oxyanions. The regioselectivity of the second step is due to a subtle balance between the nature of the phosphane, the bulkiness, and the electronic properties of the substituents. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)