Protective groups tetrahydropyran

Acetals and ketals are very important protecting groups in solution-phase synthesis, but only a few constructs have been used as linkers in solid-phase synthesis (Tab. 3.3). The THP-linker (22) (tetrahydropyran) was introduced by Ellman [54] in order to provide a linker allowing the protection of alcohols, phenols and nitrogen functionalities in the presence of pyridinium toluene sulfonate, and the resulting structures are stable towards strong bases and nucleophiles. Other acetal-linkers have also been used for the attachment of alcohols [55, 56]. Formation of diastereomers caused by the chirality of these linkers is certainly a drawback. Other ketal tinkers tike... 

In 2007, another departure from carbonyl-type activation was marked by Kotke and Schreiner in the organocatalytic tetrahydropyran and 2-methoxypropene protection of alcohols, phenols, and other ROH substrates [118, 145], These derivatives offered a further synthetically useful acid-free contribution to protective group chemistry [146]. The 9-catalyzed tetrahydropyranylation with 3,4-dihydro-2H-pyran (DHP) as reactant and solvent was described to be applicable to a broad spectrum of hydroxy functionalities and furnished the corresponding tetrahydro-pyranyl-substituted ethers, that is, mixed acetals, at mild conditions and with good to excellent yields. Primary and secondary alcohols can be THP-protected to afford 1-8 at room temperature and at loadings ranging from 0.001 to 1.0mol% thiourea... 

Unsaturated tetrahydropyran derivatives have received only cursory attention in the literature as heterocyclic monomers. 2,3-Dihydropyran and several of its substituted derivatives apparently undergo cationic polymerization in a manner typical of vinyl ethers (72MI11103), while tetrahydropyranyl esters of methacrylic acid (123) are fairly typical free radically polymerizable monomers (Scheme 35) (74MI11105). The THP group was used in this study as a protecting group for the acid functionality, and it was found that deprotection of polymers (124) could be accomplished under extremely mild conditions. 

For example the 0-tetrahydropyran.yl derivative of 3g- hydroxy 17-oxo 5-androstene 8 reacted on the bianion and give after metha-nolysis of protective group the 3g, 178— dihydoxy 5-androstene 17a- propanoic acid y-lactone 9 (4). ... 

The most common use of tetrahydropyran derivatives is as protecting groups you met this in Chapter 24 and you can see an example later in the chapter, on p. 1132. 

In this section, the formation and cleavage of eight protecting groups for alcohols and phenols are presented acetate acetonides for diols benzyl ether para-methoxybenzyl (PMB) ether methyl ether methoxymethylene (MOM) ether ferf-butyldiphenylsilyl (TBDPS) silyl ether and tetrahydropyran (THP). 

The C-5-lithiation of pyrazoles requires the absence of the A-hydrogen removable iV-protecting groups that have been used include phenylsulfonyl," trimethylsilylethoxymethyl, hydroxymethyl," methylsulfo-nyl," dimethylaminosulfonyl," tetrahydropyran-2-yl, and pyrrolidin-l-ylmethyl. Lithiation of 1-benzyloxypyrazole" or 3-benzyloxyisothiazole" takes place at C-5 and of 1-substituted pyrazole IV-oxides at C-3. °... 

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