4- Methyl-2-hydroxyacetophenone

Phenyl-3,6-dihydro-l,3,4-oxadiazin-2-one (50) is a high temperature blowing agent used primarily for polycarbonates (qv). It is prepared by the reaction of a-hydroxyacetophenone and methyl carbazate (52), made from hydrazine and dimethyl carbonate (175) ... 

The treatment of 2-hydroxyacetophenone with hydroxylamine-O-sulfonic acid in dilute aqueous base produced 3-methyl-1,2-benzisoxazole. The mechanism was reported to be a C(2)—C(3) ring closure via intermediate (560) (Scheme 171). Salicylaldehyde failed to cyclize with dilute base, but with 20% KOH and hydroxylamine-O-sulfonic acid the transformation to 1,2-benzisoxazole succeeded (76MI41600). Kemp and Woodward isolated an oxime sulfonate (561) from salicylaldehyde and hydroxylamine-O-sulfonic acid and the subsequent decomposition gave 1,2-benzisoxazole in 95% yield (65T3019). 

Since two quaternary atoms and four CH atoms appear in the C NMR spectrum, the latter with a benzenoid coupling constant of 7-9 Hz, this is a disubstituted benzene ring, and the C signal with 5c = 162.2 fits a phenoxy C atom. The keto carbonyl (5c = 204.9) and methyl (5c = 26.6) resonances therefore point to an acetyl group as the only meaningful second substituent. Accordingly, it must be either o- or m-hydroxyacetophenone A or B the para isomer would show only four benzenoid C signals because of the molecular symmetry. 

Both the benzoyl and the methyl radicals react with the double bond of the monomer and thus initiate the polymerization. Other types of photoinitiators, like 1-benzoylcyclohexanol or 2,2-dimethyl-2-hydroxyacetophenone, were shown to be as efficient as DMPA in initiating the polymerization of acrylate monomers (15,16) however, their absorption in the near UV is less pronounced so that the overall rate of the laser-induced polymerization is substantially... 

Methyl o-tolyl ketone. (6) wo-Propyl phenyl ketone. (11) w-Hydroxyacetophenone. 

Di-ter2-butylphenol 2,4,5-Trichlorophenol Phenyl salicylate Methyl 4-hydroxybenzoate 4-Hydroxyacetophenone Ethyl 4-hydroxybenzoate 4-Hydroxybenzaldehyde Pentachlorophenol 4-Chloro-2-nitrophenol 4-Nitrophenol... 

The furanoid ring in benzo[6 ]furan is susceptible to attack by oxidants. Permanganate and chromic acid give derivatives of 2-hydroxybenzoic acid with compounds unsubstituted at the 3-position, but compounds with a 3-methyl or a 3-aryl substituent give derivatives of 2-hydroxyacetophenone or 2-hydroxybenzophenone. Ozonolysis of benzo[6]furan affords 2-hydroxybenzoic acid, 2-hydroxybenzaldehyde and some catechol produced via its diformate. Before the advent of NMR spectroscopy these methods were used in structural elucidation of benzofuranoid natural products, as in the case of O-methyleuparin (Scheme 26). 

An interesting conversion of 2,6-dimethylpyran -4-one (408) into 7-methyl-5-phenylchromone (410) is achieved by reaction with the anion of acetophenone and cycliz-ation of the 2-hydroxyacetophenone (409) (77AP744). 

Upon treatment with a base, the activated methyl group in 2-hydroxyacetophenone is converted into a carbanion. Claisen condensation with an ester gives rise to a 1,3-diketone, the sodium salt of which may be isolated although this process is usually unnecessary. Cyclization to the chromone occurs readily in acid solution (Scheme 147). 

The presence of a substituent on the original methyl group of the hydroxyacetophenone prevents formation of the labile 3-acylchromone but otherwise has little effect provided the substituent is not solvolyzed. A number of 3-substituted chromones have been obtained in this manner (55JOC38). 

Salicylic acid derivatives serve a similar purpose to 2-hydroxyacetophenones in a number of chromone syntheses, acting as a precursor of the 1,3-diketone fragment. For instance, a Claisen reaction between methyl 2-methoxybenzoate and acetone takes place in the presence of sodium to give the diketone. Demethylation occurs on reaction with hydriodic acid with concomitant ring closure to the chromone (00CB1998). The corresponding naphthol derivatives are a source of benzochromones (52JOC1419). 

Hydroxyacetophenone and related compounds are attractive precursors of chromanones, most notably in the synthesis of their 2-phenyl derivatives. Being adjacent to the carbonyl group, the methyl group of the acetophenone is activated and forms a carbanion on treatment with base. Subsequent condensation with a carbonyl compound which lacks an a-hydrogen atom leads to a 1,3-dicarbonyl or an enone system which readily cyclizes to a chromanone. Thus, methyl formate affords the chromanone (591) (53MI22400) and formaldehyde has been used in the synthesis of 3-methylchroman-4-one from o-hydroxypropiophenone (68T949). 

On HZSM5 both hydroxyacetophenones are formed by trans-acylation. Disproportionation (reaction e) probably does not exist because of steric contraints. Moreover since ortho-hydroxyacetophenone does not react with phenylacetate (probably for the same reason) to give ortho-acetoxyacetophenone, reaction g cannot take place. On the other hand, the formation of products resulting from the oligomerization of ketene (dehydroacetic acid, 6-methyl 4-acetoxy 2-pyrone, reaction h) is favoured presumably because of the confinement effect in the zeolite. These compounds are supposed to be to a large extent responsible for the deactivation of HZSM5. 

A mixture of. sy/i-benzaldoxime 1 (10 mmol, 1.21 g) or 2-hydroxyacetophenone oxime 4 (10 mmol, 1.52 g) and one equivalent of 98% anhydrous zinc chloride (10 mmol, 1.36 g) was introduced in a Pyrex tube and submitted to microwave irradiation for 20 min in the Synthewave S402 monomode reactor at 140 °C. The mixture was cooled to room temperature and dissolved in methanol and then filtered through silica gel. Products were analyzed by capillary gas chromatography using methyl benzoate as an internal standard and compared by NMR with authentic samples. 

The p-cyanophenol derivative 57 was selectively transformed into the linear tricyclic cyclobutene derivative 58 (Scheme 5.11, reaction 24) [57]. The hydroxyace-tophenone derivative 59, carrying two additional methyl groups at the benzene ring, yields selectively the angular tricyclic cyclobutene derivative 60 (reaction 25) [58]. It should be stressed here that the back-reaction to the corresponding cyclooctatriene compound is inhibited by the methyl substituent at the cyclobutene moiety of 60. Chiral induction was performed with derivatives carrying a chiral ester or amide function on the hydroxyacetophenone ring [59]. 

In the reaction of ammonia, sulfur and o-hydroxyacetophenone the methyl group of the ketone is so functionalized that the 2//-imidazoline-5-thione (149) is formed. The reaction proceeds best in the presence of pyridine, and involves formation of a phenylglyoxylic thioamide (148) in the first instance (Scheme 84). The ring closure of (148) resembles similar reactions discussed earlier (Section 4.08.1.2.2(1)). 

The excretion of N-a-acetylkynurenine and kynurenic, xanthurenic, and o-aminohippuric acids was, in all the cases investigated, within the normal range, while 2-amino-3-hydroxyacetophenone and xanthurenic acid 8-methyl ether were always absent. 

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