8‑Alkoxy- and 8‑Aryloxy-BODIPYs: Straightforward Fluorescent Tagging of Alcohols and Phenols

We
demonstrate herein that both alcohols and phenols can be tagged
with a BODIPY (borondipyrromethene) moiety to yield highly fluorescent
products. Thus, 8-(methylthio)-BODIPY (1) undergoes an
SNAr-type reaction with a host of alcohols and phenols
in the presence of a base and a Cu­(I) additive. The BODIPY dyes bearing
alkoxy or nonfunctionalized phenoxy moieties are characterized by
a highly efficient fluorescence emission, regardless of the media,
in the blue-green part of the visible region. Complementary to this,
the presence of electron-donor groups at the aryl ring leads to an
intramolecular charge-transfer process, which quenches the fluorescence
mainly in polar media. In addition to simple alcohols and phenols,
four natural products (eugenol, menthol, cholesterol, and estrone)
were labeled in a simple fashion. X-ray structures of the cholesterol
and estrone derivatives are discussed. In fact, the BODIPY bearing
cholesterol stands out as a bright fluorescence biological marker.