O-Hydroxystyrene

Foster, K. L. Baker, S. Brousmiche, D. W. Wan, P. o-Quinone methide formation from excited state intramolecular proton transfer (ESIPT) in an o-hydroxystyrene. J. Photochem. Photobiol. A Chem. 1999, 129, 157-163. 

Rhodococcus sp. Strain WU-K2R A Rhodococcus strain capable of sulfur-specific desulfurization of benzothiophene, naphthothiophene (NT), and some of their alkyl derivatives was reported [35]. The metabolites of BT desulfurization were BT sulfone, benzo[c][l,2]oxanthiin S-oxide, benzo[c][l,2]oxanthiin S,S-dioxide, o-hydroxystyrene, 2,(2 -hydroxyphenyl)ethan-l-al, and benzofuran. The NT metabolites were NT sulfone, 2 -hydroxynaphthyl ethene, and naphtho[2,l-b]furan [35], The exact biochemical pathway was not determined, however, part of the pathway for BT desulfurization was speculated to be similar to Paenibacillus All-2. 

The desulfurization pathway was proposed to be BT -> BT sulfone -> benzo[e][l,2]oxanthiin S-oxide -> o-hydroxystyrene. Additionally, formation of the intermediate benzo(e)(l,2)oxathiin S,S dioxide was inferred to a side pathway resulting in formation of benzofuran as shown in Fig. 7. This pathway is similar to that reported for Sinorhizobium KT55, Paenibacillus sp. strain All-2 and R. erythropolis KT462. 

Yates and coworkers have examined the mechanism for photohydration of o-OH-8. The addition of strong acid causes an increase in the rate of quenching of the photochemically excited state of o-OH-8, and in the rate of hydration of o-OH-8 to form l-(o-hydroxyphenyl)ethanol. This provides evidence that quenching by acid is due to protonation of the singlet excited state o-OH-8 to form the quinone methide 9, which then undergoes rapid addition of water.22 Fig. 1 shows that the quantum yields for the photochemical hydration of p-hydroxystyrene (closed circles) and o-hydroxystyrene (open circles) are similar for reactions in acidic solution, but the quantum yield for hydration of o-hydroxystyrene levels off to a pH-independent value at around pH 3, where the yield for hydration of p-hydroxystyrene continues to decrease.25 The quantum yield for the photochemical reaction of o-hydroxystyrene remains pH-independent until pH pAa of 10 for the phenol oxygen, and the photochemical efficiency of the reaction then decreases, as the concentration of the phenol decreases at pH > pAa = 10.25 These data provide strong evidence that the o-hydroxyl substituent of substrate participates directly in the protonation of the alkene double bond of o-OH-8 (kiso, Scheme 7), in a process that has been named excited state intramolecular proton transfer (ESIPT).26... 

Fig. 1 The pH profile for absolute quantum yields (Oabs) for the photohydration reaction of o-hydroxystyrene (open circles) and p-hydroxystyrene (closed circles). Reprinted with permission of the American Chemical Society from Ref.25...

In contrast, a Markovnikov addition of water was reported in the irradiation of a variety of o-hydroxystyrenes, again in aqueous acetonitrile, with the formation of 2-(2-hydroxyphenyl)ethanols. In this case, an intramolecular proton transfer from the excited state of the styrene was envisaged as the first step of the reaction [51]. A similar mechanism was postulated in the photohydratation of m-hydroxy-1,1 -diaryl alkenes that gave the corresponding 1,1-diarylethanols, although direct protonation of the P-carbon by water competed in some cases [52]. 

The homogeneous unimolecular decomposition of o-hydroxy-2-phenvlethyl chloride yielded mainly benzodihydrofuran, HC1 and much less o-hydroxystyrene. The rate was significantly higher than that of phenylethyl chloride and ethyl chloride (Table 28). According to the nature of the product formation and the kinetic data, the OH provided anchimeric assistance in the elimination process. The mechanism proposed is described in equations 87 and 88. 

FIGURE 6.19 Reaction scheme for dihydrobenzofuran o-hydroxystyrene isomerization. All the energy values are calculated relative to the reactant. 

Benzothio-phene (BT) Oi 0 10 Rhodococcus (56,90), Rhodococcus, Gordona (85), Paenibacillus (93) Sulfone, BcOTOBTHO, BTHOa, BcOTO, HBESi-,HPEal, BFUBTHO, BcOTO, o-hydroxystyrene... 

The first, organocatalytic chemo-, [ElZ)- and enantioselective alkeny-lation of indole-derived hydrojylactams (283) using o-hydroxystyrenes (284) as a source of alkenyl group, has been established via the chiral phenanthtyl substituted BINOL (286) catalysing tandem reactions to give 7,8,13,13Z>-tetrahydro-57f-benzo[l,2]indolizino[8,7-Z)]indol-5-one derivatives (285) (Scheme 77). ° ... 

Carpanone 58 is a lignan isolated from the bark of the Carpano tree it possesses no element of symmetry by having five contiguous asymmetric centers. Its biomimetic synthesis, first reported by Chapman et al., was accomplished by diastereoselective oxidative homocoupling of an electron-rich o-hydroxystyrene followed by rapid CKi/o-selective inverse-electron demanding Diels-Alder... 

Ylides of Sulphur, Selenium, Tellurium, and Related Structures 359 was proposed that sulphene formation was involved in each reaction, with the triphenylphosphine adding to the sulphene and displacing SO2 to afford the phosphonium ylide, which was protonated by the conjugate acid of the amine. Sulphenes have been reported to react with tropone to afford an adduct which rearranged on heating to an o-hydroxystyrene (lOQ. ... 

An interesting mechanistic variant of styrene-amine addition upon direct irradiation is presented by the reaction of the o-hydroxystyrene 28 with MeNHj to yield the adduct 28a in 62% yield (Scheme 17). The initial step in the reaction mechanism is deprotonation of the acidic singlet state of 28 by the amine to yield a phenolate-ammonium ion pair. Reprotonation of the phenolate ion yields a zwitterion, which is trapped by the nucleophilic amine. Thus, the amine serves both as a base and as a nucleophile in this reaction. 

Yates and co-workers observed a similar reaction for o-hydroxystyrene (33) (formation of 34) ... 

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