Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Protective groups acetyl

The procedure is not usually applicable to aminosulphonic acids owing to the interaction between the amino group and the phosphorus pentachloride. If, however, the chlorosulphonic acid is prepared by diazotisation and treatment with a solution of cuprous chloride in hydrochloric acid, the crystalline chlorosulphonamide and chlorosulphonanilide may be obtained in the usual way. With some compounds, the amino group may be protected by acetylation. Sulphonic acids derived from a phenol or naphthol cannot be converted into the sulphonyl chlorides by the phosphorus pentachloride method. [Pg.553]

We shall describe a specific synthetic example for each protective group given above. Regiosdective proteaion is generally only possible if there are hydroxyl groups of different sterical hindrance (prim < sec < tert equatorial < axial). Acetylation has usually been effected with acetic anhydride. The acetylation of less reactive hydroxyl groups is catalyzed by DMAP (see p.l44f.). Acetates are stable toward oxidation with chromium trioxide in pyridine and have been used, for example, for protection of steroids (H.J.E. Loewenthal, 1959), carbohydrates (M.L. Wolfrom, 1963 J.M. Williams, 1967), and nucleosides (A.M. Micbelson, 1963). The most common deacetylation procedures are ammonolysis with NH in CH OH and methanolysis with KjCO, or sodium methoxide. [Pg.158]

An important reaction parameter is the choice of the base and NajCO or NaOAc have been shown to be preferable to EtjN in some systems[2]. The inclusion of NH4CI has also been found to speed reaction[2]. An optimization of the cyclization of A -allyl-2-benzyloxy-6-bromo-4-nitroaniline which achieved a 96% yield found EtjN to be the preferred base[3]. The use of acetyl or inethanesulfonyl as N-protecting groups is sometimes advantageous (see Entries 4 and 5, Table 4.1). [Pg.36]

After the N acetyl protecting group has served its purpose it may be removed by hydrolysis liberating the ammo group... [Pg.941]

Nitration. Direct nitration of aromatic amines with nitric acid is not a satisfactory method, because the amino group is susceptible to oxidation. The amino group can be protected by acetylation, and the acetylamino derivative is then used in the nitration step. Nitration of acetanilide in sulfuric acid yields the 4-nitro compound that is hydroly2ed to -rutroaruline [100-01-6]. [Pg.231]

A recent publication describes the protection of a S-keto-A" system via its eniminium salt, permitting enol acetylation of a 20-ketone, epoxidation, hydrolysis and finally removal of the A-ring protecting group. [Pg.186]

In an attempt to protect thiophenols during electrophilic substitution reactions on the aromatic ring, the three substituted thioethers were prepared. After acetylation of the aromatic ring (with moderate yields), the protective group was converted to the disulfide in moderate yields, 50-60%, by oxidation with hydrogen peroxide/boiling mineral acid, nitric acid, or acidic potassium permanganate. ... [Pg.479]

In synthesis of the alkaloid tjipanazole E (19b), the required symmetric dichloro-indolo[2,3-fl]carbazole 20a was obtained in a two-step procedure starting fi-om 4-chlorophenylhydrazine hydrochloride and 1,2-cyclohexanedione employing a Fischer indolization. Subsequent attachment of an acetyl-protected glucopyranosyl moiety to one of the nitrogens, followed by cleavage of the protective groups with ammonia in methanol, produced the desired natural product (91X7739). [Pg.6]

An interesting observation was made in regard to the polymeriza-bility of N-acylhydroxyproline derivatives The monomers with the smallest protecting groups such as N-acetyl and N-pivaloylhydroxy-proline gave rise to the polymers with the lowest molecular weights (Table 1). When these monomers were polymerized, the initially... [Pg.203]

In this reaction the fully acetylated sugar 5- or 6-phosphates were phos-phorylated and the protecting groups removed by alkali. Only a-1-phosphates were isolated and no evidence of the -anomers could be detected. [Pg.142]


See other pages where Protective groups acetyl is mentioned: [Pg.173]    [Pg.173]    [Pg.160]    [Pg.217]    [Pg.220]    [Pg.1137]    [Pg.464]    [Pg.282]    [Pg.91]    [Pg.349]    [Pg.387]    [Pg.1137]    [Pg.384]    [Pg.550]    [Pg.190]    [Pg.23]    [Pg.100]    [Pg.7]    [Pg.9]    [Pg.167]    [Pg.174]    [Pg.129]    [Pg.140]    [Pg.501]    [Pg.551]    [Pg.707]    [Pg.719]    [Pg.58]    [Pg.137]    [Pg.138]    [Pg.366]    [Pg.503]    [Pg.204]    [Pg.204]    [Pg.192]    [Pg.3]    [Pg.852]    [Pg.1251]   
See also in sourсe #XX -- [ Pg.14 , Pg.17 ]




SEARCH



Acetyl group

Acetyl protecting groups

Acetyl protecting groups

© 2024 chempedia.info