2.3 Conclusion

 In summary, an efficient method has been developed for the preparation of

unsymmetrical imidazolidines and 2,3-dihydro-1H-benzimidazoles via Mannich reactions

of diamines with benzotriazole and formaldehyde, followed by nucleophilic substitution

of the benzotriazolyl group with other functionalities. Compared to the previous methods

(multi-step and low yields) for the preparation of unsymmetrical imidazolidines,

[86S657] [77LAC956] [00JHC57] our method needs only two steps, utilizes easily

available starting materials, and generally affords the desired products in good to

excellent yields.

 2.4 Experimental Section

 THF or toluene was distilled from sodium-benzophenone prior to use. Melting

points are uncorrected. 1H, 13C NMR spectra were recorded (300 MHz and 75 MHz

respectively) in CDC13 (with TMS for 1H and chloroform-d for 13C as the internal

reference), unless otherwise stated. Elemental analyses were performed on a Carlo Erba-

1106 instrument. Optical rotation values were measured with the use of the sodium D

line. Column chromatography was performed on silica gel (200-425 mesh), neutral

alumina (60-325 mesh) or basic alumina (60-325 mesh). All of the reactions were

carried out under N2.

2.4.1 General Procedure for the Preparation of 1-Substituted-3-(benzotriazolvlmethyl)
Imidazolidines 2.9a-c.

 A mixture of a N-substituted-1,2-ethanediamine 2.8a-c (3.0 mmol), BtH (0.36 g,

3.0 mmol), and formaldehyde (37% aqueous solution, 0.49 g, 6 mmol) in CH3OH/H20

(10 mL/5 mL) was stirred for 4 h at 20 OC. For 2.9a, the precipitate formed was filtered

and washed with cool Et20. For 2.9b,c, the mixture was extracted with EtOAc, the