Table 1. Evaluations of Conditions for the Reaction of 1a and 2a to Afford 3a^a.

entry	2a (equiv)	CF3SO3H (equiv)	time (min)	yield of 3a (%)b	yield of 4a (%)b
1	3.0	0.45	60	70	0
			150	94	6
2c	3.0	0.45	60	60	0
			150	94	6
3c	3.0	0.45	82	40	1
			147	69	3
4	3.0	0.20	60	46	0
5	3.0	0.10	60	39	0
6	3.0	0.05	60	32	0
7	3.0	0.01	60	31	0
			120	60	0
			240	94	6
8	1.0	0.01	48	45	2
			75	78	5
9d	1.0	0.01	48	14	0
			75	24	1
10e	3.0	0.001	30	18	0
			100	38	0
11e	2.0	0.001	30	23	0
			100	58	1
12e	1.5	0.001	30	29	2
			100	88	2
13e	1.1	0.001	30	30	0
			100	90	2

^aFor the reactions, to a solution of 2a (indicated equivalents relative to 1a) and CF₃SO₃H (indicated equivalents relative to 1a) in CDCl₃ (1.0 mL), 1a (0.029 mmol, 1.0 equiv) was added, and the mixture was heated at 60 °C. See the Supporting Information for details.

^bDetermined by ¹H NMR analysis.

^cTo a solution of 1a (0.029 mmol, 1.0 equiv) and 2a (indicated equivalents) in CDCl₃ (1.0 mL) (entry 2) or in C₆D₅CD₃ (1.0 mL) (entry 3), CF₃SO₃H (indicated equivalents) was added, and the mixture was heated at 60 °C.

^d2b (2.0 equiv) was added.

^eA 0.11 mmol scale reaction.