Phenols protection-deprotection reactions

Nafion-H has been shown to be effective in a variety of protection-deprotection reactions including (9-trialkylsilylation of alcohols, phenols, and carboxylic acids, as well as the preparation and methanolysis of tetrahydropyranyl (THP) ethers.672 However, when compared, for example, with HBF4-silica or Nafion nanocomposites,... 

A useful process for phenol protection and analysis is exemplified by tlie reaction of estrone with perfluorotoluene [72] (equation 8) The hydroxyl function replaces the 4 fluorme in high yield, and the hydroxyl may be deprotected in 87% yield on treatment with hydroxide... 

The thermolytic deprotection reaction is extremely clean. The infrared spectrum of the deprotected polymer is identical to that of the phenolic precursor as is the ultraviolet spectrum. The molecular weight of the phenolic copolymer precursor is unchanged by the t-BOC protection reaction/thermolysis cycle based on GPC data. 

Boger s synthesis commenced with the preparation of the left-hand fi agment 155. A sequence of phenol protection of 151, aldehyde oxidation, Curtius rearrangement, tosylation, nitro reduction, Boc protection, and Pb(OAc)4 mediated oxidation afforded quinodiimide 152. A key Diels-Alder reaction gave 153 in good yield. Treatment of 153 in a sequence of oxonolysis, aromatization, Boc deprotection, cyclization to the lactam, A-tosyl removal, indole reduction, and selective Boc protection afforded 154. Conversion of the lactam to the... 

In general, these compounds were synthesized from appropriately substituted and selectively protected phenolic esters. A reaction sequence that consisted of selective deprotection, oxidation to the quinoid system, and addition of an amino acid gave vinylogous esters. Linkage to the trans-decalin building blocks with an exocyclic double bond was achieved with a Suzuki coupling of substituted arylboronic acids to the corresponding decalin-derived vinyl bromides. Reduction of... 

The indole compound was described by Flynn et al. [73] and is prepared in a similar manner as the thiophene 103 and furan 108. One method involved a similar synthesis as described in Scheme 25, using the relevant starting material. However, an alternative synthesis involved a one-pot, room-temperature synthesis, Scheme 27. The o-iodotrifluoroacetanilide 110 was coupled to the alkyne 111 under Sonogashira conditions in MeCN. K2CO3 and the aryliodo compound 107 was added and the reaction stirred to produce the protected product 112 with a 77% yield. Deprotection to the corresponding phenol 113 was performed using AICI3. 

The yield of crown ether can be increased to more than 80% by using a longer stepwise route in which the initial catechol is partially protected. Reaction of the phenol (34) with bis(2-chloroethyl) ether (33) forms intermediate (35) which after deprotection can react with a further molecule of bis(2-chloroethyl) ether to give dibenzo[18]crown-6. 

Notes This alcohol protecting is easily attached and readily removed by Lewis acids such as zinc bromide and titanium tetrachloride. Phenols can be protected (reaction of the sodium salt with MEMC1) and deprotected with TFA. More easily removed than the MOM group. 

Perfluorotoluene and pentafluoropyridine have been proposed as reagents for protecting alcohols and phenols as perfluoroaryl ethers, a reaction which takes place under mild PTC conditions. Deprotection involves demethoxylation with NaOMe in DMF at 60 C (Scheme 18 R = phenyl, steroidal).158... 

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