Table 1.

The optimization of reaction conditions^a.

Entry	Catalyst	Base	P1 (%)b	A1″ (%)b
1	[Ru(p-cymene)Cl2]2	K2CO3	<10	8
2	[Ru(p-cymene)Cl2]2	t-BuOK	< 10	42
3	[Ru(p-cymene)Cl2]2	Mg(OMe)2	90	0
4	[Ru(p-cymene)Cl2]2	MeOK	< 10	53
5	-	Mg(OMe)2	0	0
6	[Ru(p-cymene)Cl2]2	–	0	0
7	[Cp*IrCl2]2	Mg(OMe)2	85	trace
8	[IrCl(COD)]2	Mg(OMe)2	74	trace
9	[Ru(p-cymene)Cl2]2	Mg(OMe)2	(0, 0, 61)c	(0, 0, 0)c
10	[Ru(p-cymene)Cl2]2	Mg(OMe)2	(58, 91, 86)d	(0, 0, 0)d
11	[Ru(p-cymene)Cl2]2	Mg(OMe)2	(33, 25)e	(0, 0)e
12	[Ru(p-cymene)Cl2]2	Mg(OMe)2	(42, 30)f	(0, 0)f

Cp*: 1,2,3,4,5-pentamethylcyclopentadiene, cod: 1,5-cyclooctadiene, DMF: N,N-dimethylformamide.

^aUnless otherwise stated, the reaction in MeOH (1 mL) was performed with A1 (0.2 mmol), B1 (0.2 mmol), cat. (1 mol%), base (0.75 eq), (CH₂O)_n (10 eq) at 65 °C for 18 h under N₂ protection.

^bNMR yield by using anisole as the internal standard.

^cYields are with respect to the use of DMF, 1,4-dioxane, ethanol as the solvent, respectively.

^dYields are with respect to the temperature at 45 °C, 55 °C, 75 °C, respectively.

^eYields are with respect to 0.5 and 0.3 eq of Mg(OMe)₂, respectively.

^fYields are with respect to 8 and 5 eq (CH₂O)_n, respectively.