Protective groups reactivities

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. 

Ethers are among the most used protective groups in organic synthesis. They vary from the simplest, most robust, methyl ether to the more elaborate, substituted, trityl ethers developed for use in nucleotide synthesis. They are formed and removed under a wide variety of conditions. Some of the ethers that have been used to protect alcohols are included in Reactivity Chart 1. ... 

Some of the protective groups for diols are listed in Reactivity Chart 3. 

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

Derivatives of carbonyl compounds that have been used as protective groups in synthetic schemes are described in this chapter some of the more important protective groups are listed in Reactivity Chart 5. ... 

In this chapter detailed information is pn vided for the more useful protective groups (some of which are included in Reactivity Charts 8-10) structures and references are given for protective groups that seem to have more limited use. ... 

These 108 reagents are used in the Reactivity Charts that have been prepared for each class of protective groups. The reagents and some of their properties are described on the following pages. 

R (reacts) indicates that the protected compound reacts readily, but that the original functional group is not restored. The protective group may be changed to a new protective group (eq. 1) or to a reactive intermediate (eq. 2), or the protective group may be unstable to the reaction conditions and react further (eq. 3). 

The number used to designate a protective group (PG) in a Reactivity Chart is the same as that used in the body of the text in the first edition. 

Protective group numbers in the Reactivity Charts are not continuous, since not all of the protective groups described in the text are included in the charts. The protective groups that are included in the Reactivity Charts are in general those that have been used most widely consequently, considerable experimental information is available for them. 

Reactivity Chart -10. Protection for the Amino Group SjDocial — NH Protective Groups... 

Two new sections on the protection for indoles, imidazoles, and pyrroles, and protection for the amide — NH are included. They are separated from the regular amines because their chemical properties are sufficienth different to affect the chemistry of protection and deprotection. The Reactivity Charts in Chapter 8 are identical to those in the first edition. The chart number appears beside the name of each protective group when it is first discussed. 

The process of selecting a protective group involves a number of discrete steps. First, the proposed scheme is summarized, with reactants, reaction conditions, and products delineated for each synthetic step. Next, the relative reactivities of the functional groups in each reactant... 

Polymer supported reagents, catalysts, protecting groups, and mediators can be used in place of the corresponding small molecule materials (Sherrington, 1991 Sundell and Nasman, 1993). The reactive species is tightly bound to a macromolecular support which immobilizes it. This generally makes toxic, noxious, or corrosive materials much safer. The use of polystyrene sulfonic acid catalyst for the manufacture of methyl r-butyl... 

Steric hindrance due to the presence of other substituents a to the carbonyl group may diminish reactivity during the formation of ketone protecting groups. Thus a marked decrease in reactivity has been observed with 2- or... 

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