Structure-reactivity relationships in (2-hydroxyethyl)benzophenone photoremovable protecting Groups

• Published in: Tetrahedron Vol. 66; no. 17; pp. 3147 - 3151
• Main Authors: Pirrung, Michael C., Roy, Biswajit Gopal, Gadamsetty, Surendra
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 24.04.2010; Elsevier
• Subjects: Benzophenone; Chemical reactivity; Chemistry; Chemistry, Organic; Dienol; Elimination; Exact sciences and technology; General and physical chemistry; Noncondensed benzenic compounds; Organic chemistry; Photochemistry; Photoenolization; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Physical Sciences; Preparations and properties; Reactivity and mechanisms; Science & Technology; Photoenolization; Dienol; Elimination; Benzophenone; MECHANISMS; ZINC BOROHYDRIDE; Solvent effect; Substituent effect; Benzophenone derivatives; Molecular structure; Deprotection; Photochemical reaction; Organic synthesis; Ester; Structure activity relation; Carboxylic acid; Hexane; Chemical reactivity; Chemical synthesis; Methanol; Protecting group; Analog; Acetonitrile; Irradiation; Benzenic compound; Inclusion compound; Sensitizer
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/j.tet.2010.02.087

A detailed study of substituent effects on the photochemical conversion of esters of (2-hydroxyethyl)benzophenone to the carboxylic acid was performed with the aim of improving on the reactivity of the parent, which was first reported decades ago. Over 20 derivatives were prepared, 10 of which exhibit some level of photochemical reactivity, but none of them is appreciably better than the original. The reaction did not respond to a thioxanthone as a sensitizer or the inclusion of base to facilitate elimination. Solvent effects on the reaction also seem to be small, with the exception of the perfluorphenyl analog, which is totally unreactive in hexanes but behaves normally in methanol or acetonitrile. These neglected protecting groups may still prove useful in organic synthesis, with fairly rapid deprotection even with long-wavelength irradiation. [Display omitted]