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Carbonates to protect phenols

Catechols can be protected as diethers or diesters by methods that have been described to protect phenols. However, formation of cyclic acetals and ketals (e.g., methylenedioxy, acetonide, cyclohexylidenedioxy, diphenylmethylenedioxy derivatives) or cyclic esters (e.g., borates or carbonates) selectively protects the two adjacent hydroxyl groups in the presence of isolated phenol groups. [Pg.170]

Carbamate esters to protect alcohols, 62 to protect amines, 104, 387-388 to protect phenols, 167 Carbonate esters to protect alcohols, 104 to protect phenols, 165-167 Carbonates, cyclic, see Cyclic carbonate esters... [Pg.235]

TrichloroethyI carbonates to protect alcohols, 105-106 to protect phenols, 166... [Pg.243]

Another synthesis of the cortisol side chain from a C17-keto-steroid is shown in Figure 20. Treatment of a C3-protected steroid 3,3-ethanedyidimercapto-androst-4-ene-ll,17-dione [112743-82-5] (144) with a tnhaloacetate, 2inc, and a Lewis acid produces (145). Addition of a phenol and potassium carbonate to (145) in refluxing butanone yields the aryl vinyl ether (146). Concomitant reduction of the C20-ester and the Cll-ketone of (146) with lithium aluminum hydride forms (147). Deprotection of the C3-thioketal, followed by treatment of (148) with y /(7-chlotopetben2oic acid, produces epoxide (149). Hydrolysis of (149) under acidic conditions yields cortisol (29) (181). [Pg.434]

Allyl carbonates can be cleaved by nucleophiles under palladium(O) catalysis. Allyl carbonates have been proposed for side-chain protection of serine and threonine, and their stability under conditions of /VT moc or /V-Boc deprotection has been demonstrated [107]. Prolonged treatment with nucleophiles (e.g., 20% piperidine in DMF, 24 h) can, however, lead to deprotection of Alloc-protected phenols [108,109]. Carbohydrates [110], tyrosine derivatives [107], and other phenols have been protected as allyl ethers, and deprotection could be achieved by palladium-mediated allylic substitution (Entry 9, Table 7.8). 9-Fluorenyl carbonates have been used as protected intermediates for the solid-phase synthesis of oligosaccharides [111]. Deprotection was achieved by treatment with NEt3/DCM (8 2) at room temperature. [Pg.224]

Alkynyl complexes. These complexes, which are readily available by reaction of an alkynyllithium with chromium carbonyl followed by methylation with CH3OSO2F, undergo facile Diels-Alder reactions with dienes to provide a general route to ,p-un-saturated chromium carbene complexes. The latter undergo benzannelation or cyclo-hexadienone annelation on reaction with an alkyne. A (trimethylsilyl)ethynyl complex is useful because benzannelation results in migration of silicon from carbon to oxygen to provide a protected phenol. [Pg.135]


See other pages where Carbonates to protect phenols is mentioned: [Pg.243]    [Pg.205]    [Pg.199]    [Pg.384]    [Pg.89]    [Pg.127]    [Pg.422]    [Pg.36]    [Pg.95]    [Pg.106]    [Pg.199]    [Pg.107]    [Pg.716]    [Pg.136]    [Pg.153]    [Pg.95]    [Pg.106]    [Pg.663]    [Pg.332]   
See also in sourсe #XX -- [ Pg.416 ]




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Phenol carbons

Phenolic carbons

Phenols carbonation

Phenols, protection

Protection carbonate

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