Observation of transient cyclohexadienones during the aqueous bromination of phenols. Mechanisms of enolization

Abstract

Supplementary Material Available: Experimental procedures for the syntheses of compounds 2-33, their systematic names, characterization, and a modified method for determining Xa and -AG°values at more dilute concentrations (24 pages). Ordering information is given on any current masthead page.

Theoretical study on the mechanism of thieno[3,2‐b]benzofuran bromination: the importance of Lewis and non‐Lewis type NBOs interactions along the reaction path

“…It is known that the structure of attacking species in electrophilic bromination depends on the reaction conditions: when a strong Lewis acid is used with the bromine, the attacking electrophile may be a positive bromonium cation Br + . In the presence of polar solvents, the attacking electrophile may be a neutral Br 2 molecule polarized by the solvent . In the absence of a catalyst or polar solvents, and using nonpolar solvents, the attacking bromine molecule can be polarized by the π‐electron‐rich aromatic rings system of heterocycle .…”

“…[33][34][35][36][37] In the absence of a catalyst or polar solvents, and using nonpolar solvents, the attacking bromine molecule can be polarized by the π-electronrich aromatic rings system of heterocycle. [33][34][35][36][37] Bromination of thieno[3,2-b]benzofuran takes place under mild reaction conditions in the absence of catalysis using nonpolar solvents. [5,6] Under these experimental conditions, bromination reaction proceeds with excellent selectivity but very slowly.…”

“…In the presence of polar solvents, the attacking electrophile may be a neutral Br 2 molecule polarized by the solvent . In the absence of a catalyst or polar solvents, and using nonpolar solvents, the attacking bromine molecule can be polarized by the π‐electron‐rich aromatic rings system of heterocycle . Bromination of thieno[3,2‐ b ]benzofuran takes place under mild reaction conditions in the absence of catalysis using nonpolar solvents .…”

Vanadate-dependent bromoperoxidases from Ascophyllum nodosum in the synthesis of brominated phenols and pyrroles

“…Comparing the absolute value of ρ to references from the literature shows that the reactivity and selectivity-determining bromoelectrophile is molecular bromine. 106 The estimated reaction parameter for tetrabutylammonium tribromide-mediated phenol bromination (ρ ∼ −3.1) is similar to controls starting from bromine (Table 11). This observation implies that tribromide decomposes into bromide and bromine prior to phenol bromination, as predicted by reaction theory (Section 3).…”

General and Theoretical Aspects of Phenols

“…Hydrogen transfer from oxygen to carbon indeed disrupts the phenyl ring and this disfavours the ketone form. However, the latter intervene as crucial intermediates during the phenol decomposition, in the oxidative metabolism of aromatic compounds (the 'NIH-shift'), in the reactions of arene oxides, the photo-Fries rearrangement, the Kolbe-Schmitt and the Reimer-Tiemann reactions 184,185,468 . Both cyclohexa-2,4-dien-1-one 27 and cyclohexa-2,5-dien-1-one 28 Let us remember that the energy difference between phenol 26 and both keto isomers 27 and 28 amount to 73 and 69 kJ mol −1 , respectively ( Figure 31).…”