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Protecting group
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group in order to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. 
Acetal protection of a ketone during reduction of an ester Protecting groups are more commonly used in small-scale laboratory work and initial development than in industrial production processes because their use adds additional steps and material costs to the process. However, the availability of a cheap chiral building block can overcome these additional costs (e.g. shikimic acid for oseltamivir). While additional synthetic steps are required for protection and deprotection, reactions are typically much cleaner, proceed in higher yields, and require less optimization with protecting groups than without.
Common protecting groupsAlcohol protecting groupsProtection of alcohols:
Amine protecting groupsProtection of amines:
Carbonyl protecting groupsProtection of carbonyl groups:
Carboxylic acid protecting groupsProtection of carboxylic acids:
Miscellaneous
Orthogonal protectionOrthogonal protection is a strategy allowing the deprotection of multiple protective groups one at the time each with a dedicated set of reaction conditions without affecting the other. It was introduced in the field of peptide synthesis by Robert Bruce Merrifield in 1977 [3]. As a proof of concept orthogonal deprotection is demonstrated in a photochemical transesterification by trimethylsilyldiazomethane utilizing the kinetic isotope effect [4]:
Due to this effect the quantum yield for deprotection of the right-side ester group is reduced and it stays intact. Significantly by placing the deuterium atoms next to the left-side ester group or by changing the wavelength to 254 nm the other monoarene is obtained. CriticismIn a 2007 paper [5] Phil Baran notes that even though the textbooks state that the use of protective groups is unavoidable and ideally easily added and removed, in practical terms in organic synthesis their use adds two synthetic steps in a chemical sequence and sometimes dramatically lowers chemical yield. Crucially, added complexity impedes the use of synthetic total synthesis in drug discovery. In contrast biomimetic synthesis does not employ protective groups. As an alternative, Baran presented a novel protective-group free synthesis of the compound hapalindole U. The previously published synthesis [6] [7] [8] according to Baran, contained 20 steps with multiple protective group manipulations (two confirmed):
External links
References
de:Schutzgruppe fr:Groupe protecteur ja:??? sv:Kemisk skyddsgrupp zh:??? 
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