2,5-Dimethylphenacyl Esters: A Photoremovable Protecting Group for Carboxylic Acids
| Authors | |
|---|---|
| Year of publication | 2001 |
| Type | Article in Periodical |
| Magazine / Source | Journal of Physical Chemistry A |
| MU Faculty or unit | |
| Citation | |
| Field | Organic chemistry |
| Keywords | photochemistry |
| Description | Irradiation of 2,5-dimethylphenacyl (DMP) esters (1a) in benzene or cyclohexane solutions produces the corresponding free carboxylic acids (2a) in high chemical yields, along with 6-methyl-1-indanone (3). In methanol, 2-(methoxymethyl)-5-methylacetophenone (4) is formed as a co-product. Quantum yields for the photorelease of the DMP group are higher in non-polar solvents, fi = 0.2, than in methanol, fi = 0.1. The photoreaction is initiated by efficient photoenolization, fi = 1. Three transient intermediates were identified by laser flash photolysis of 1a, the triplet state photoenol and the two ground state photoenols of Z and E configuration. Release of the acids 2a occurs predominantly from the E isomer, which has a lifetime of about 2 ms in methanol and 0.5 s in benzene solution. The present data are essential for potential applications of the DMP moiety as a photoremovable protecting group in organic synthesis or biochemistry ("caged compounds"). |
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