Use of protecting groups

In case an organic molecule contains two reactive groups and you want to use only one of these groups, the other group has to be protected, the desired reaction completed and the protecting group removed. For example 

Reactions of this type are common in the synthesis of fine chemicals, pharmaceuticals, pesticides etc. In the above protection, benzyl chloride (a known hazard) and the waste generated after deprotection should be handled carefully. 

Another reaction involving protection of a keto function by using 1,2-ethanediol is as follows  

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The use of protecting groups other than ketals appears to have been rather limited. The Merck group introduced the use of semicarbazones. 

Synthesis of a peptide of prescribed sequence requires the use of protecting groups to minimize the number of possible reactions. 

The steps involved in automated oligonucleotide synthesis illustrate the current use of protective groups in phosphate chemistry (Scheme 1). Oligonucleotide synthesis involves the protection and deprotection of the 5 -OH, the amino groups on adenine, guanine, and cytosine, and -OH groups on phosphorus. 

Minimize derivatives. Syntheses should be designed with minimal use of protecting groups to avoid extra steps and reduce waste. 

In this section, we consider several syntheses of six illustrative compounds. We examine the retrosynthetic plans and discuss crucial bond-forming steps and the means of stereochemical control. In this discussion, we have the benefit of hindsight in being able to look at successfully completed syntheses. This retrospective analysis can serve to illustrate the issues that arise in planning a synthesis and provide examples of solutions that have been developed. The individual syntheses also provide many examples of the synthetic transformations presented in the previous chapters and of the use of protective groups in the synthesis of complex molecules. The syntheses shown... 

The use of protecting groups in the synthesis was minimized by utilizing the N-picolinyl and N-acetyl groups not only as structural components of 1 but also to tune the reactivity of the intermediates. 

The formation of peptides from Leuchs anhydrides proceeds without the use of protecting groups, and no racemisation occurs. However, the use of phosgene cannot be considered a prebiotic process ... 

A different strategy for the preparation of silsesquioxanes containing silanol groups has been put forward by Matasumoto et al., which involves the stepwise formation of siloxane linkages and the use of protection groups. In this... 

Moody and Rahimtoola reported a short synthesis of staurosporinone (293) without the use of protecting groups at the indole or the lactam nitrogen (761,762). This route involves an intramolecular Diels-Alder reaction of the pyrano[4,3- 7]indol-3-one 1325 and a subsequent cyclization by nitrene insertion. The pyrano[4,3-l7]indol-3-one 1325 was obtained in four steps from ethyl indol-2-yl... 

Gilbert and Van Vranken described the synthesis of tjipanazole F2 (372) by introduction of the halide and the glycosidic substituent at the heterocyclic skeleton without the use of protecting groups and with complete control of regioselectivity... 

The Holton, Nicolaou, Danishefsky, and Wender syntheses of baccatin III structures employ various cyclic intermediates and take advantage of stereochemical features built into these rings to control subsequent reaction stereochemistry. These syntheses also provide numerous examples of the selective use of protective groups to differentiate between the several hydroxy groups that are present in the intermediates. 

In the following, the emphasis has mainly been put on transformations of aldonolactones without any use of protection group chemistry. After selective... 

Disubstituted-3,6-dihydro-l,2-dioxines can be dihydroxylated readily with OsOa to furnish the 4,5-diols 73 in yields of 33-98% and with de values not less than 90%. Subsequent reduction of the peroxy bond allowed the stereospecific synthesis of tetraols 74 without the use of protecting groups <2006JOC7236>. 

For the sulfation of peptides that do not contain methionine residues, the use of protecting groups that are cleaved by hydrogenolysis represents, independent of the sulfation procedure followed, the safest approach (see Scheme 7)J52,96"... 

Despite the use of protecting group strategies, compounds containing amino moieties are often plagued with poor reactivities in CM. For instance, the CM reactions of unsubstituted allylic carbamates typically proceed in low yields (Scheme The predominant side-products obtained in these reactions are alkene homodimerization and... 

N,N-dimethylpropyllithium (50,51). However, primary amine-ended polymers have required the use of protecting groups because of the mutual reactivity of primary amines and living lithiomacromolecules. 

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