Photochemical Cleavage of Benzylic C-O Bond Facilitated by an Ortho or Meta Amino Group.

The excited state meta effect, also known as the meta-ortho effect, results from selective electron transmission from an electron-donating group to the meta and ortho sites on an aromatic ring in its first excited singlet state. This effect facilitates photochemical cleavage of benzylic C-O or C-N bond to release the corresponding alcohol, carboxylic acid, or amine when an electron-donating amino group is at the meta position, as demonstrated in our recent work of using a 3-diethylaminobenzyl (DEABn) group as an effective photolabile protecting group (PPG). Herein, we demonstrate that an ortho amino group can also facilitate benzylic C-O bond cleavage to release an alcohol or carboxylic acid. However, an amino group at the meta position results in a PPG with better overall chemical and photochemical properties.