page_title: Photolabile protecting group
section_title: Benzyl-based PPGs
hierarchical_section_title: Photolabile protecting group / Main classifications / Benzyl-based PPGs
caption_attribution_description: English: Benzyl based PPGs
context_page_description: A photolabile protecting group is a chemical modification to a molecule that can be removed with light. PPGs allow enable high degrees of chemoselectivity as they allow researchers to control spatial, temporal and concentration variables with light. Control of these variables is valuable as it enables multiple PPG applications, including orthogonality in systems with multiple protecting groups. As the removal of a PPG does not require chemical reagents, the photocleavage of a PPG is often referred to as "traceless reagent processes", and is often used in biological model systems and multistep organic syntheses. Since their introduction in 1962, numerous PPGs have been developed and utilized in a variety of wide-ranging applications from protein science to photoresists. Due to the large number of reported protecting groups, PPGs are often categorized by their major functional group; three of the most common classifications are detailed below.
context_section_description: Barltrop and Schofield first demonstrated the use of a benzyl-based PPG, structural variations have focused on substitution to the benzene ring, as well as extension of the aromatic core. For example, insertion of a m,m’-dimethoxy substituent was shown to increase the chemical yield ~75% due to what has been termed the “excited state meta effect.” However, this substitution is only able to release good leaving groups such as carbamates and carboxylates. Additionally, the addition of an o-hydroxy group enables the release of alcohols, phenols and carboxylic acids due to the proximity of the phenolic hydroxy to the benzylic leaving group. Finally, the carbon skeleton has been expanded to include PPGs based on naphthalene, anthracene, phenanthrene, pyrene and perylene cores, resulting in varied chemical and quantum yields, as well as irradiation wavelengths and times.
caption: Figure 5: Benzyl-based PPGs with polycyclic aromatic cores: A) benzene; B) naphthalene; C) anthracene; D) phenanthrene; E) phyene and; F) perylene.
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