Synthesis of the benzimidazoles^a.

Entry	1, R1, R2	2, R3, R4	3, yield (%)
1	1a, H, Bn	2a, Me, Me	3a, 91
2	1b, Me, Bn	2a, Me, Me	3b, 81
3	1c, F, Bn	2a, Me, Me	3c, 83
4	1a, H, Bn	2b, Et, Et	3d, 89
5	1b, Me, Bn	2b, Et, Et	3e, 78
6	1c, F, Bn	2b, Et, Et	3f, 82
7	1a, H, Bn	2c, Ph, Cy	3g, 74
8	1b, Me, Bn	2c, Ph, Cy	3h, 59
9	1c, F, Bn	2c, Ph, Cy	3i, 63
10	1d, H, Me	2a, Me, Me	3j, 89
11	1e, Me, Me	2a, Me, Me	3k, 69
12	1f, F, Me	2a, Me, Me	3l, 68
13	1d, H, Me	2b, Et, Et	3m, 86
14	1e, Me, Me	2b, Et, Et	3n, 64
15	1f, F, Me	2b, Et, Et	3o, 62
16	1d, H, Me	2c, Ph, Cy	3p, 73
17	1e, Me, Me	2c, Ph, Cy	3q, 58
18	1f, F, Me	2c, Ph, Cy	3r, 60
19	1g, H, Ph	2a, Me, Me	3s, 88
20	1g, H, Ph	2b, Et, Et	3t, 85
21	1g, H, Ph	2c, Ph, Cy	3u, 73

^aReaction conditions: a mixture of 1 (0.6 mmol), 2 (0.6 mmol) and CF₃COOH (0.6 mmol) in MeCN (2.0 mmol) while stirring in open flask at room temperature.