At this juncture the pivotal C-H oxidation of the tertiary C-H bond at C-4' was explored using nearly every set of conditions that could conceivably function in such a chemoselectively demanding setting. Thus, radical, dioxirane, halogenative, directing group-based, and others were evaluated to no avail (across a range of differentially protected analogs, see SI). Even enzymatic systems were studied which so far have proven fruitless. 11 With this spectacular failure in hand, attention thus turned to the decarboxylative chlorination approach.