Second-order rate constants k₂ for the reactions of the enamines 4 or 5 with the benzhydrylium tetrafluoroborates 7 and Mayr nucleophilicity parameters for 4 and 5 (acetonitrile, 20 °C).

Enamine	Electrophile	Mayr Ea	k 2 (M−1 s−1)	N, sN
4	7d	–7.02	7.06 × 101	9.25, 0.84
	7e	–7.69	2.14 × 101
	7f	–8.22	7.74
	7g	–8.76	2.42
5	7a	–2.19	6.92 × 104	7.74, 0.87
	7b	–3.85	1.96 × 103
			(1.75 × 103)b
	7c	–5.53	8.84 × 101
			(5.49 × 101)b

^aElectrophilicity parameters E (as defined in eqn (1) and reported in ref. 13).

^bIn dichloromethane. With further data in ESI, N(s_N) = 7.06 (1.11) was calculated for 5 in CH₂Cl₂.