Catalyst and solvent screening for the manganese-catalyzed transfer hydrogenation of 1,3-diphenylurea (1a)^a.

Entry	[Mn]	Co-solvent	2a/%	3a/%	4a/%
1	Mn–I	—	54	19	63
2	Mn–II	—	47	7	77
3	Mn–III	—	52	—	85
4	Mn–IV	—	71	45	54
5	—	—	46	—	90
6	Mn–IV	CH2Cl2b	39	5	35
7	Mn–IV	THFb	78	64	19
8	Mn–IV	Tolueneb	91	89	—
9	Mn–IV	1,4-Dioxaneb	73	60	14
10c	Mn–IV	Tolueneb	46	9	73

^aReaction conditions: 1a (0.5 mmol), catalyst [Mn] (2 mol%), KOtBu (6 mol%), iPrOH (2 mL), 120 °C, 16 h. Yields were determined by GC using mesitylene as the internal standard.

^biPrOH (1 mL) and cosolvent (1 mL).

^c100 °C.