Conditions optimization for the bromolactonization.

Entrya	Bromine source	Frequency	Time	Yield (%)b
1	NBS	20 Hz	10 min	14
2c	NBS	—	120 min	10
3d	NBS	—	120 min	0
4	NBS	30 Hz	30 min	20
5	NBS	30 Hz	60 min	33
6	NBS	30 Hz	120 min	99 (97)e
7	DBDMH	20 Hz	10 min	99

^aReactions were conducted using a Retsch mixer mill (MM 400) in a 10 mL zirconium oxide chambers with alkenoic acid 1a (0.2 mmol) and bromine source (0.22 mmol) at ambient temperature in the absence of light.

^bDetermined by NMR spectroscopy with dibromomethane as the internal standard.

^cReaction conducted in dichloromethane (0.2 M).

^dReaction was conducted under neat conditions and the solid samples were mixed by a magnetic stirrer bar.

^eIsolated yield.