Throughout our optimization studies, 4-phenyl benzaldehyde (I), methyltriphenylphosphonium bromide (a, PPh3MeBr), and a solid base were ball-milled in a 7 mL Teflon™ milling vessel containing one 12 mm stainless steel ball. The reactions were carried out at a defined frequency using an IST636 mixer mill (for detailed optimization data, see SI).