Table 2.

Base optimization studies for reversible transamination^[a]

Entry	Base	Equivalents	Distribution1/2[b]	Equilibrium conversion [%][c]
1	NEt3	4	34/66	88
2	NEt3	1	67/33	44
3	NMI	4	no reaction	–
4	NMM	4	93/7	9
5	NMP	4	92/8	11
6	DIPEA	4	30/70	93
7	DMAP	4[d]	71/29	39
8	DABCO	4	25/75	100
9	C1	4	25/75	100
10	C2	4	26/74	100
11	DABCO	0.2	71/29	39
12	C2	0.2	43/57	76
13	C1	0.2	25/75	100
14	C3	0.2[d]	98/2	3
15	C4	0.2	98/2	3
16	C5	0.2	no reaction	–
17	C1	0.1	35/65	87
18	C1	0.05	50/50	66
19	DBU	0.1	decomposition	–
20	TMG	0.1	decomposition	–

[a] Conditions: imine 1 (0.25 mmol), base (n equivalents), 3 Å MS (10 mg), anhydrous MeCN (0.25 mL), 50 °C, N₂, 24 h. NMI=N-methylimidazole, NMM=N-methylmorpholine, NMP=N-methylpyrrolidine, DIPEA=diisopropylethylamine, DMAP=4-dimethylaminopyridine, DABCO=1,4-diazabicyclo[2.2.2]octane, TMG=N,N,N′,N′-tetramethyl-1,3-propanediamine; for the structures of C1–C5 (see Figure 2). [b] Analyzed by ¹H NMR spectroscopy. [c] Conversion towards the equilibrium position, 25/75 for 1/2. [d] Low solubility.