Table 1. Reactivity of Different Carbodiimides toward Methanol with and without the Catalyst^a.

entry	C(NR)2	precatalyst	T (°C)	t (h)	conversion (%)b
1	R = iPr	ZnEt2	60	1	>99
2			60	21	16
3	R = Cy	ZnEt2	60	2	>99
4			60	2
5	R = tBu	ZnEt2	60	30	27
6			60	48
7	R = p-tol	ZnEt2	25	1.5	>99
8			60	4	64
9	R = Dipp	ZnEt2	80	120	97 [89]c
10			80	120	<1

^aReaction conditions: 0.50 mmol carbodiimide, 0.50 mmol MeOH, 0.025 mmol precatalyst (25 μL, 1.0 M solution of ZnEt₂ in hexanes), 500 μL of C₆D₆, and Si(SiMe₃)₄ (0.01 mmol) as an internal standard.

^bBased on ¹H NMR of the reaction crude versus internal standard.

^cIsolated yield from the preparative–scale reaction.