Table 1.

Optimization of the reaction conditions.^[a] Adapted with permission from Ref. [58]. Copyright 2021, American Chemical Society.

Entry	Deviation from standard conditions	11 aaa yield[b] [%]
1	none	98
2	no silica, no acid	n.r.
3	no silica	28
4	no acid	28
5	NaCl instead of silica	51
6	Na2SO4 instead of silica	69
7	30 mg of silica	89
8	100 mg of silica	88
9	NH4Cl instead of AcOH	93
10	Yb(OTf)3 (0.1 equiv.) instead of AcOH	91
11	Cs2CO3 instead of AcOH	92
12	39 balls instead of 20	95
13	0.20 mmol scale	89[c]
14	reflux in EtOH, AcOH (2.0 equiv.), 24 h	n.r.

[a] Reaction conditions: 8 a (0.10 mmol), 9 a (0.17 mmol), 10 aaa (0.15 mmol), planetary ball mill (PM) with ZrO₂ Mg‐stabilized jars (size: 12 mL) and 20 ZrO₂ Y‐stabilized balls (size: 5 mm). [b] Determined by quantitative ¹⁹F NMR spectroscopy [standard: 4,4′‐bis‐(trifluoromethyl)benzophenone]. [c] Yield after flash column chromatography. n.r.=no result.