Table 1.

Screening of the base for Biltz synthesis to Phenytoin (4) by RAM.^a)

Entry	Base	Yield [%]b), c)
1	CaO	n.r.
2	K2CO3	n.r.
3	t‐BuOK	n.r.
4	KOH	46
5	KOHd), g)	52g)
6	KOHe)	48
7f)	KOHf)	60
8	KOHg)	43
9h)	KOHh)	55h)

^a)Reaction was conducted in a 10 mL screw cap glass vial. Reaction conditions: benzil (5.35 mmol,1.0 equiv.), urea (5.35 mmol, 1.0 equiv.) and KOH (10.7 mmol, 2.0 equiv.) were accelerated at 100 g during 180 min;

^b)The yield refers to the isolated product after work‐up. Work‐up: the RAM crude was dissolved in water and the precipitate, consisting of unreacted benzil and 3a,6a‐diphenylglycoluril^{[ 37 ]} (5) (c.f., Table 3 and Supporting Information), was filtered off. The water filtrate was acidified with an aqueous solution of 10% citric acid till pH 4. Phenytoin (4) precipitated off, it was filtered and washed with water till neutral pH, then dried in vacuo in the presence of P₂O₅;

^c)n.r. = No reaction;

^d)Benzil and urea were pre‐grinded in a mortar before the reaction;

^e)The reagents (benzil and urea) and the base were pre‐mixed at 60 g during 5 min;

^f)The mixing occurred by three cycles of 60 min. each, with 5 min rest in between each cycle. The hard agglomerate formed after each cycle was scratched manually, before the subsequent mixing cycle;

^g)KOH (4.0 equiv.) were used;

^h)The potassium ureate salt^{[ 37 ]} was formed first by mixing 1 urea (1.0 equiv.) and KOH (2.0 equiv.) at 80 g for 60 min, leading a deliquescent viscous liquid, then benzil was added and the mixture was reacted at 100 g during 180 min.