title: Palladium-catalyzed synthesis of 2,3-dihydro-2-ylidene-1,4-benzodioxins.
abstract: Palladium-catalyzed condensation of benzene-1,2-diol with various propargylic carbonates afforded regio- and stereoselectively 2,3-dihydro-2-ylidene-1,4-benzodioxins. The reaction is suggested to proceed by the formation of a (sigma-allenyl)palladium complex, followed by the intermolecular attack of the phenoxide ion on this complex to generate a new (sigma-allyl)palladium complex in equilibrium with the corresponding (eta(3)-allyl)palladium complex. Intramolecular attack of the phenoxide ion afforded the corresponding benzodioxan compound. This last attack occurs predominantly at the more electrophilic end of the (eta(3)-allyl)palladium intermediate. The Z- or E-stereochemistry of the products was established by (1)H NMR and proton NOE measurements and also by X-ray analysis on an example. The Z-stereochemistry generally observed is in agreement with the formation of this (eta(3)-allyl)palladium intermediate. However, in the case of tertiary propargylic carbonates, the E-stereochemistry generally observed could be explained by an intramolecular attack of the phenoxide ion on the intermediate (sigma-allyl)palladium complex, in slow equilibrium with the (eta(3)-allyl)palladium complex.
authors.affiliation: Laboratoire de Synthèse Asymétrique, UMR CNRS 5622, CPE Lyon, Université Claude Bernard Lyon 1, 43 boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France.
authors.forename: J R
authors.initials: JR
authors.lastname: Labrosse
authors.forename: P
authors.initials: P
authors.lastname: Lhoste
authors.forename: D
authors.initials: D
authors.lastname: Sinou
mesh_terms: D018674:Adrenergic Antagonists / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D004791:Enzyme Inhibitors / Q000138:chemical synthesis; D016859:Lipoxygenase Inhibitors; D015394:Molecular Structure; D010165:Palladium / Q000737:chemistry; D011412:Propanolamines / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D018674:Adrenergic Antagonists; D004791:Enzyme Inhibitors; D016859:Lipoxygenase Inhibitors; D011412:Propanolamines; C006708:benzoral; D010165:Palladium