Ortho-hydroxy groups

Sections D through H of Scheme 3.2 involve oxygen nucleophiles. The hydrolysis reactions in Entries 12 and 13 both involve benzylic positions. The reaction site in Entry 13 is further activated by the ERG substituents on the ring. Entries 14 to 17 are examples of base-catalyzed ether formation. The selectivity of the reaction in Entry 17 for the meta-hydroxy group is an example of a fairly common observation in aromatic systems. The ortho-hydroxy group is more acidic and probably also stabilized by chelation, making it less reactive. 

Upon oxidation with IBD, a series of o-hydroxyacetophenones and related compounds 57 give the corresponding 2-methoxycoumaran-3-ones 59 [84JCS(CC)1342] (Scheme 19). These reactions probably occur via intramolecular participation of the ortho hydroxy group, which attacks the a-carbon of the intermediate 58 to yield the intermediate product 58a. A similar reaction occurs when /3-diketones 60 are oxidized with IBD-KOH/MeOH,... 

On the basis of (a) the necessity of an ortho hydroxy group for photo-chromism, (h) the ability of isolated anil molecules to show photochro-mism, and (c) the similarity of the deeply colored photoinduced form to... 

Section 1.3.2.A). The loose proton of the methyl group in cation radicals is capable of forming an intramolecular hydrogen bond with the oxygen atom of the ortho-hydroxy group. This hydrogen bonding keeps the proton within the fused cycle, blocks the formation of the or-tho-hydroxybenzyl radical, and retards or prevents the consequent oxidation. 

Acid dyes include metal-complexed azo structures, where the metals used are cobalt, chromium, and iron.10 Examples are 1 1 and 2 3 chromium complexes and 1 2 cobalt complexes, where the numbers employed represent the ratio of metal atoms to dye molecules. Metal-complexed dyes can be formed inside textile fibers by treating suitably dyed fibers with a solution containing metal ions.11 In this case, the metal-free forms of these azo dyes are known as mordant dyes and contain mainly ortho, ortho -bis-hydroxy or ortho-carboxy, ortho -hydroxy groups (e.g., C.I. Mordant Black 11, Mordant Yellow 8, and Mordant Orange 6). When the metal complexes are formed prior to the dye application process, the resultant dyes are known as... 

Phenols with ortho hydroxy groups such as pyrocatechol can give chelates by bonding the 2" anion as in (11-XXIII) producing complex anions such as [Cr(02C6H4)3]3 and [Cr(C0)3(02C6H4)]2-.96... 

Benzoxetanes 214 were observed among the photolysis products of diar-yldiazomethanes containing an ortho hydroxy group [91JCS(P1)471], Substituted oxetane carboxylic acid 215 was first synthesized in preparative... 

Nierenstein reaction. Formation of omega-chloroacetophenones by reaction of diazomethane in dry ether with aroyl chlorides. Coumaranones are obtained if an ortho-hydroxy group is present. 

The presence of the ortho-hydroxy group is essential for the observation of both types of chromisms, and the mechanism involves intramolecular proton transfer via a six-membered-ring transition state, producing enol-keto tautomeric species, with the spectra of the keto forms showing a bathochromic shift (Scheme 16). 

A mechanistic study performed with 177 and analogues showed thermal (at 110°C and 130 °C) and photostabilizing (at 50 °C) effects in PP. The authors suggest involvement of the ortho-hydroxy group in the benzophenone moiety in the CB mechanism [280]. 

Intramolecular participation by the ortho hydroxy group occurs in the reaction of substituted o-hydroxyacetophenones, yielding the corresponding coumaran-3-ones (eq 12). ... 

When the acyl group carries a second functionality (double or triple bond, hydroxyl group, carbonyl group, etc.), interaction of the latter with the ortho-hydroxy group, subsequent to the rearrangement step, may be a general principle for the construction of heterocyclic ring systems. This has been applied... 

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