title: Multiple mechanisms in Pd(II)-catalyzed S(N)2' reactions of allylic alcohols.
abstract: Density functional calculations and experiments were used to examine mechanisms of Pd(II) catalyzed intramolecular cyclization and dehydration in acyclic and bicyclic monoallylic diols, a formal S(N)2' reaction. In contrast to the previously proposed syn-oxypalladation mechanism for acyclic monoallylic diols, calculations and experiments strongly suggest that hydrogen bonding templates a hydroxyl group and Pd addition across the alkene and provides a low energy pathway via anti-addition (anti-oxypalladation) followed by intramolecular proton transfer and anti-elimination of water. This anti-addition, anti-elimination pathway also provides a simple rationale for the observed stereospecificity. For bicyclic monoallylic diol compounds, Pd(II) is capable of promoting either anti- or syn-addition. In addition, palladium chloride ligands can mediate proton transfer to promote dehydration when direct intramolecular proton transfer between diol groups is impossible.
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, Florida 32611, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ghebreghiorgis
authors.forename: Brian H
authors.initials: BH
authors.lastname: Kirk
authors.forename: Aaron
authors.initials: A
authors.lastname: Aponick
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Ess
mesh_terms: D002384:Catalysis; D003500:Cyclization; D004988:Ethers, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry; D006860:Hydrogen Bonding; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D020005:Propanols / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory
chemical_list: D004988:Ethers, Cyclic; D008024:Ligands; D009942:Organometallic Compounds; D020005:Propanols; D011522:Protons; C006463:allyl alcohol; D010165:Palladium