Catechols, protection

Some of the more important phenol and catechol protective groups are included in Reactivity Chart 4. ... 

The intention was to produce the pyridone moieties toward the end of the synthetic scheme, hence the catechol protecting groups chosen were benzyl with the intention of removing them during the hydroxyl-directed enamide reduction step. 

Carboxylic acids, protection of, 224-276 as amides and hydrazides, 270-276 as esters, 227-270 Reactivity Chart 6, 433-436 S-Carboxymethyl thioethers, to protect thiophenols, 294-295 Catechols, protection of, 170-174 as cyclic acetals and ketals, 170-172 as cyclic esters, 173-174 Reactivity Chart 4, 425-428 CBZ, see Benzyl carbamates Chloroacetamides, to protect amines, 352-353... 

N-Salicylideneamines, to protect amines, 370 Selective cleavage, 411-412 of benzyl carbamates, 339-340 of benzyl ethers, 49-56 of catechol protective groups, 171 of N- vs. 5-dimethylphosphinothioyl groups, 307... 

Fig. 6. Synthesis of parabactin, starting with N1)N8-bis(2,3-dimethoxybenzoyl)spermidine. The final step (4-parabactin), involving the formation of the oxazoline, is performed without catechol protecting groups...

This selectivity has been exploited in a synthesis of terprenin 2.26, an immunosuppressant compound (Scheme 2.10). The iodobromide 2.20 underwent selective Suzuki coupling with one boronic acid 2.21 at the iodo position, then a second boronic acid 2.23 at the bromo position. This two-step process could be carried out in one pot. The unusual catechol protecting group was not wasted, but converted into a prenyl ether at the end of the synthesis by hydrolysis and a Wittig reaction. 

Formylbenzenesulfonate, 170 PROTECTION FOR CATECHOLS CYCLIC ACETALS AND KETALS... 

See also E. Haslam, Protection of Phenols and Catechols, in Protective Groups in Organic Chemistry, J. F. W. McOmie, Ed., Plenum Press, New York and London, 1973. pp. 145-182. 

Both methyl aryl and methyl alkyl ethers are cleaved under these conditions. A methylenedioxy group, used to protect a catechol, is cleaved under similar conditions in satisfactory yield methyl and ethyl esters are stable (0-20°, 2 h). °... 

PROTECTION FOR PHENOLS AND CATECHOLS 24. 4-Picolyl Ether ArOCH2-4-pyridyl (Chart 4) Formation /Cleavage ... 

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. 

A cyclic borate can be used to protect a catechol group during base-catalyzed alkylation or acylation of an isolated phenol group the borate ester is then readily hydrolyzed by dilute acid. ... 

Cyclic carbonates have been used to a limited extent only (since they are readily hydrolyzed) to protect the catechol group in a polyhydroxy benzene. 

Reactivity Chart 4. Protection for Phenois and Catechols (Continued)... 

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