. Author manuscript; available in PMC: 2014 Apr 5.

Published in final edited form as: Org Lett. 2013 Mar 11;15(7):1646–1649. doi: 10.1021/ol400427x

Table 1.

Apparent 2^nd order rate constants (M⁻¹ min⁻¹) for different ortho proton donor nucleophilic catalysts.^a

catalyst	pK_a^b	2^nd order rate constant	rel. to uncat. rxn.
(none)	--	0.10 ± 0.01	1
aniline	--	1.1 ± 0.1	11
1	2.18	2.3 ± 0.3	22
2	−1.41 ^c	0.14 ± 0.03	1.4
3	--	1.7 ± 0.2	16
4	7.29	4.1 ± 0.2	40
5	10.0	0.09 ± 0.03	0.8
6	9.29	0.25 ± 0.06	2.5
7	9.60 ^c	0.04 ± 0.02	0.4
8	9.78 ^c	0.03 ± 0.01	0.3
9	6.51 ^c	0.05 ± 0.06	0.5
10	5.63 ^c	0.12 ± 0.03	1.2

Reaction conditions: 18 µM NBD Hydrazine, 1 mM 4-nitrobenzaldehyde, 1 mM catalyst in 10:1 PBS (pH 7.4):DMF, 23 °C. Reaction monitored at 504 nm.

pK_a values of acidic moiety from literature (see text for references).