Acetylation acetoxy derivatives

The most simple l, 4-dithiocin system, which is stable, is the 6-acetoxy derivative 13, which can be synthesized from 1,4-dithiocin-6(57/)-onc (12) by trapping its enolate with acetyl chloride.7 9... 

In a related procedure, even benzene and substituted benzenes (e.g., PhMe, PhCl, xylenes) can be converted to phenols in good yields with sodium perborate F3CS020H. " Aromatic amines, N-acyl amines, and phenols were hydroxylated with H2O2 in SbFs—HF. Pyridine and quinoline were converted to their 2-acetoxy derivatives in high yields with acetyl hypofluorite AcOF at -75°C. ... 

The enzyme can also catalyze the transfer of an acetyl group from an N-acetylated hydroxylamine (hydroxamic acid) to form an acetoxy product, i.e., an N to O transacetylation and this pathway does not require acetyl Co-A (12). A-hydroxy-4-acetylaminobiphenyl provides an example of this conversion as shown in Figure 7.7. The significance of this pathway is that it leads to the activation of the hydroxamic acid because acetoxy derivatives of aromatic amines are chemically reactive and many are carcinogens such as the heterocyclic amines formed when meat is heated to a high temperature, e.g., 2-amino-1-mcthyl-6-phenylirnidaz()[4,5-i ]pyri(linc. 

It is sometimes necessary either to acetylate the hydroxyl group first and then methylate this ester or to protect one hydroxyl group while another is alkylated, for instance. A promising technique of selective acetylation is therefore of interest when 5,7-dihy-droxyisoflavone (538) is heated with acetic anhydride-pyridine, the 7-acetoxy derivative is formed, but acetic anhydride-perchloric acid yields the 5-acetoxy isomer (79CC264). 

In addition to the preparation of a- and /3-hydrastine described above from the betaine (64), another conversion of a tetrahydroberberine into hydrastine has been reported. Acetylophiocarpine, on treatment with ethyl chloroformate, gives the acetoxy-derivative of (88), which can be hydrolysed to the hydroxymethyl compound and then oxidized to the aldehyde by pyridinium perchlorate. Hydrolysis of the acetoxyl group afforded the hemi-acetal (93 R = H), conversion of which into the mixed acetal (93 R = Et) protected the aldehyde system during reduction of N—C02Et to NMe by lithium aluminium hydride. Hydrolysis of the acetal, followed by oxidation, then gave a-hydrastine, and a similar sequence of reactions starting from O-acetyl-13-epi-ophiocarpine afforded / -hydrastine.119 Methods of synthesis of alkaloids of this group have been reviewed.120... 

In contrast to intermolecular photoaldols, which can be manipulated with facility, intramolecular cycloadducts undergo retro-[2 + 2] cycloaddition when subjected to hydrolytic conditions. In an alternative protocol, oxymercuration of (229) afforded a-mercurio ketone (230 42%) which was acetylated under standard conditions to provide 1,4-diketone (231) quantitatively. Similarly, epoxidation of (229) provided functionalized photoaldol (232), which was hydrolyzed and acetylated to form a-acetoxy derivative (233). Finally, hydrolysis of (234) (4 1 THF/0.1 N HCl) gave lactol (235) in nearly quantitative yield, illustrating the utility of the intramolecular furan carbonyl photocycloaddition in spirocycle formation. 

Dehydrogenation of pyrimido[4,5-d]azepines 532,540 (R = Ph), 543, and 548 (R = Ph) was unsuccessful over palladium-on-carbon catalyst in boiling decalin or with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) in boiling dioxane. However, when pyrimido[4,5-6] azepine 549 was treated with palladium-on-carbon catalyst, dihydropyrimido[4,5-6]azepines 551 and 552 could be isolated chromatographically in 10 and 5% yields, respectively (78H275). When pyrimido[4,5-6]azepine 549 was heated in dioxane in the presence of DDQ, 5,6-dihydropyrimido[4,5-overall yield when pyrimido[4,5-carbon tetrachloride, and the resulting bromohydrin 553 was reduced with zinc powder in acetic acid at 60°C. Acetylation of the bromohydrin with acetic anhydride in pyridine gave the more stable acetoxy derivative 554. 

Figure VIII shows the enantiomeric composition of various hydroxy- and acetoxyacid esters and of if -hexa-and -octalactone isolated from pineapple. Methyl 3-hydroxyhexanoate and methyl 3-acetoxyhexanoate are mainly of the (S)-configuration corresponding to intermediates of B-oxidation. The optical purity of the 5-acetoxy esters is lower than of the 3-acetoxy derivatives. The lactones were mainly of the (R)-configuration. Figure IX presents a possible pathway to explain the formation of these compounds. Methyl (S)-(+)-3-hydroxyhexanoate and methyl (S)-3-acetoxyhexanoate may be derived from (S)-3-hydroxyhexanoyl-CoA by transacylation with methanol and acetyl-CoA, respectively. The biosynthesis of 5-hydroxyacids is still unknown, but they may be formed by elongation of 3-hydroxyacids with malonyl-ACP. This hypothesis could explain their varying enantiomeric composition relative to the 3-hydroxyacids. However, hydration of unsaturated acids and/or the reduction of 5-oxoacids may be involved.

Preparation of PhAcOZ amino acids proceeds from the chloroformate and cleavage is accomplished enzymatically with penicillin G acylase (pH 7 phosphate buffer, 25°C, NaHSOs, 40-88% yield).In a related approach, the 4-acetoxy derivative is used in this case, however, deprotection is achieved using the lipase, acetyl esterase from oranges (pH 7, NaCl buffer, 45°C, 57-70% yield). ... 

Further utility of the 4-oxazolin-2-one as a protective group (see Vol. 2) is evidenced in the synthesis of the hydroxylated tetrahydrobenzylisoquinolines of the type (59). An attempt to effect phenolic oxidative dimerization of homo-orientaline (60) gave instead, after acetylation, the 1-acetoxy-derivative (61) in low yield. A series of 5-hydroxy-6-hydroxymethyl-, 6-hydroxy-7-hydroxy-methy 1, and 7-hydroxy-6-hydroxymethyl-1 -(3,4,5-trimet hoxybenzy 1)-1,2,3,4-... 

The reaction of N-protected 3-formyl and 3-acetylindole with ra-chloroperoxybenzoic acid has been investigated. 1-Benzenesulfonyl-3-formyl and 1-acetyl-3-formyl indoles gave modest yields of 3-indolones via hydrolysis of unstable formate esters. Some of the corresponding 2-hydroxyindol-3-ones were also formed. The 3-acetoxy derivative of 1-benzenesulfonylindole is more stable and was isolated in 80% yield from the oxidation of 3-acetyl-l-benzenesulfonylindole. <94S411>... 

A fifth factor is certainly ease of preparation and in this characteristic the melt prepared thermotropic polymers are particularly favored. All of the polymers described thus far may be made in a conventional melt acidolysis process starting with the acetoxy derivatives of the hydroxyl containing monomers used. A typical polymerization scheme is shown in Figure 8, the preparation of the two component polyester derived from the acetylated hydroxybenzoic and hydroxynaphthoic acids. The polymerization may be carried out with or without added catalysts. The poly(ester-amides) commented on here, and the more recently reported aromatic, thermotropic poly(ester-carbonates) and poly(ester-imides), may all be synthesized in a similar manner. 

Nolana. In the aerial parts of N. coelestis Miers ex Dun. four 4,ll(13)-cadinadienes were discovered, e.g., the 12-acetoxy derivative (Fig. 7.4). Its congeners showed structural differences with regard to the substituents at C-4 (CH OAc) and/or the lack of the acetyl group at 120 (OH). Unfortunately, the authors neither created trivial names nor published correct chemical nomenclature (Garbarino et al. 1993). 

A series of acetoxy derivatives of androstane were deacylated in organic solvents by several lipases. The most satisfactory results were obtained with lipase from Candida cylindracea (CCL) and Candida antarctica (CAL). In some derivatives, CCL and CAL showed an overwhelming regioselectivity toward the removal of the 3p- or the IT -acetyl group and three new steroid derivatives were obtained [31] through this approach (Fig. 17). 

Acylation of 3-alkyl-6-hydroxy-l,2-benzisoxazole has also been reported (77JIC875) under Friedel-Crafts conditions to give the 7-acyl product. Fries rearrangement of 6-acetoxy-3-methyl-1,2-benzisoxazole in the presence of AICI3 at 140 °C also provides a route to the 7-acetyl-6-hydroxy derivatives (73UC541). Reactions of these kind are rare in this series. 

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