Dienones phenol acetates

In 1979, workers investigating " the dienone-phenol rearrangement treated (3) with acetic anhydride and got an unknown compound believed to be (4), Treatment with strong acid gave (5), they supposed, but they wanted to synthesise an authentic sample of (5) to check their assignment. This is a tricky problem... 

Androsta-l,4,6-triene-3,17-dione 246, when treated with ordinary acid catalysts such as acetic anhydride-para-toluenesulfonic acid, gives the meta phenolic product 247 (Scheme 5.88). However, under HF SbF5 catalysis at 50°C the phenolic product 248 is obtained in 75% yield855 (Scheme 5.88). The mechanism of the above discussed phenol-dienone and dienone-phenol rearrangement has been investigated in detail.856 857... 

The dienone-phenol rearrangement of androsta-l,4,6-trien-3,ll,17-trione has been shown to lead to two major products, the AB-aromatic acetate (180 X = O) and the corresponding lla-ol (180 X = a-OH,H). Oxidation of the naphthol (180 ... 

Zimmerman 103) applied the well known rearrangement of 4,4-disubstituted cyclohexa-2,5-dienones (e.g. the 4,4-diphenyl derivative tives the 3,4-disubstituted phenols l)). Using acetic anhydride and a small amount of concentrated sulfuric acid, 97.5 % of 3,4-diphenylphenolacetate is formed, which in turn is hydrolyzed to give 3,4-diphenylphenol. This is one of the easiest synthesis of this phenol. 2-Bromo-4,4-diphenylcyclohexa-2,5-dienone rearranges by a similar route to give a 49 % yield of 2-bromo-3,4-diphenylphenolacetate and 47 %2-bromo-4,5-diphenylphenolacetate U4). A [1.2]-phenyl shift of 4-methoxy-2,3,4,6-tetraphenyl-2,5-dienone in acetic anhydride and zinc chloride gives rise to 4-methoxy-2,3,5,6-tetraphenylacetate (m.p. 284 °C, 85% yield)115 . 

Anthrasteroids have also been formed by ordinary dienone-phenol rearrangements. Treatment of 7-oxo-5,8(9)-diene systems, either in the lojS- [lyo] or loa- [192] series, with sulphuric acid in acetic anhydride gave anthrasteroids with oxygen functions both in ring A and in the aromatic ring B. A similar reaction is reported with zinc and silver nitrate in acetic acid [ 192 J, but the mode of action of this reagent system is not known. 

Many rearrangement reactions are initiated by BF3 complexes in the presence of acetic anhydride, including the synthesis of functionalized and optically active pyrans from (+)-(/ ,R)-diethyl tartrate (Eq. 41) [74]. Other examples include the conversion of bicyclic into monocyclic [75] and tricyclic into bicyclic systems [76], the acetolysis of glycosides resulting in the formation of the fully acetylated acyclic derivative [77], and the unusual migration of nitrogen in the dienone-phenol rearrangement of an N-methoxy-/ -lactam [78]. 

The conventional dienone-phenol rearrangements of o-quinol acetates are described above. An alternative mode of restructuring to an aromatic system has been observed, exemplified by the quantitative conversion of the 2,4-dienone (155) on heating at 110 C in acetic acid to the benzylic acetate (156). The related 2,4-dienone (157) rearranges at 70-80 °C in dimethyl sulfoxide-sodium bicarbonate to the... 

The Dienone-Phenol Rearrangement. There are a number of instances known in which cyclic dienoncs yield rearranged phenols under the influence of acids.45 Wilds and Djorassi46 have shown that the dienone (LXV) could be rearranged into LXVI by heating with sulfuric acid and acetic anhydride. The structure of (LXVI) was proved by an independent synthesis. Similarly,... 

The oxidation of phenolic phenethylisoquinolines has been studied in some detail. With iron(iii) chloride the bases (68 R = H and R = OMe) have been oxidised to the homoproaporphine bases (69 R = H and OMe), and the base (70) has been oxidised to the homoproaporphine (71), which yielded the homoaporphine alkaloid multifloramine when subjected to dienone-phenol rearrangement. In this last process, when the dienone (71) was treated with concentrated hydrochloric acid in glacial acetic acid, the mixed acetal (72 R = Me), convertible into the hemiacetal (72 R = H), was isolated. ... 

Enol acetylation. Enol acetylation of steroidal ketones with acetic anhydride catalyzed by perchloric acid has been shown to be thermodynamically controlled (2,309). However, this acetylating reagent in the case of conjugated ketones gives complex mixtures of O-acylated and C-acylated products.1 Dienone-phenol rearrangements have been noted with A4-3-ketosteroids alkylated at C2 or C6.2... 

Discovery of the dienone-phenol rearrangement of quinol acetates has made possible the synthesis of dihydric phenols that were difficult of access by other routes. The starting materials are obtained from phenols and lead tetraacetate, and with acetic anhydride and sulfuric acid (Thiele acetylation) or with boron trifluoride in ether they give, respectively, di- and mono-acetyl derivatives of resorcinol or hydroquinone.309 When treated with lN-sodium hydroxide, 0-quinol acetates of type (1) undergo nucleophilic addition of an OH" ion, giving resorcinol derivatives (2).310 Occurrence of the reaction is considered... 

If this were true, only the singlet-spin isomer would need to be taken into account. The triplet-spin isomer of an ortfto-quinol acetate, obtainable by use of photosensitizers of triplet energy as low as 42 kcal/mol, reacts to give the product of a dienone-phenol rearrangement [72e]. 

Abnormal dienone-phenol rearrangement— Phenol acetates from dienones s. 11, 793... 

A. 2,i,l,()-Tetrabromo-2,5-cyclohexadien-l-one. A mixture of 66.2 g. (0.2 mole) of 2,4,6-tribromophenol (Note 1), 27.2 g. (0.2 mole) of sodium acetate trihydrate, and 400 ml. of glacial acetic acid is placed in a 1-1. Erlenmeyer flask and warmed until a clear solution is obtained. The temperature of the solution is approximately 70°. The solution is magnetically stirred and cooled to room temperature to produce a finely divided suspension of the phenol. A solution of 32 g. (0.2 mole) of bromine in 200 ml. of glacial acetic acid is added dropwise over 1 hour (Note 2). The resulting mixture is kept at room temperature for 30 minutes and is then poured onto 2 kg. of crushed ice. The yellow solid which separates is removed by suction filtration after the ice has melted, and the damp crystals are dissolved in the minimum quantity of warm chloroform (Note 3). The upper aqueous layer is removed by means of a pipet fitted with a suction bulb. The dienone crystallizes from the... 

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