Wavelength-controlled orthogonal photolysis of protecting groups.

The selective control of a chemical process by the use of an electromagnetic wave has been a challenging goal for several decades. In this article, we describe for the first time the use of a monochromatic light beam to differentiate two different reactive centers. A direct application of this concept is found in the chemistry of protecting groups. Two different photolabile protecting groups were tuned to be responsive to a specific wavelength (e.g., 254 or 420 nm). Using derivatives of the 2-nitroveratryl fragment (such as 10, sensitive at 420 nm) and 3',5'-dimethoxybenzoin fragment (such as 4, sensitive at 254 nm), it was shown that energy transfer phenomena did not erode the selectivity. Both the inter- and the intramolecular cases were studied and showed selectivities within the synthetically useful range. Hence, we could replace the traditional chemical orthogonality by a chromatic orthogonality.