Et-N NH i Et-N N
 Et-N N.H
 H H C6H4NO2-P C6H4NO2-p

 2.8b 2.23 2.24, R = Bt
 NaCN .
 2.25, R = CN
 i) p-O2NC6H4CHO; ii) BtH, HCHO

Scheme 2-4. Modification of the 2-position of the imidazolidine ring

2.2.5 Preparation of 1-Methyl-3-substituted-2,3-dihydro-l1H-benzimidazoles 2.28, 2.29.

 2,3-Dihydro-1H-benzimidazoles are usually prepared by condensation of the

corresponding N,N'-disubstituted-1,2-benzenediamines with formaldehyde.[21JCS1537]

[88JCS(P1)1939] We reported the formation of 1,3-bis(benzotriazolylmethyl)-2,3-

dihydro- 1H-benzimidazole by treatment of 1,2-benzenediamines with 1H-benzotriazole

and formaldehyde. [90CJC446] We found that condensation of N-methyl-1,2-

benzenediamine (2.26a) with benzotriazole and 2 equiv of formaldehyde produced Bt

intermediate 2.27 in 85% yield (Scheme 2-5). Compound 2.27 was obtained as a mixture

of Bt and Bt2 isomers in ca. 5.9:1 ratio, which was used directly for the subsequent

reactions.

 Reaction of 2.27 with vinyl magnesium bromide was found to give unidentifiable

products probably opening the five-membered ring. The weaker nucleophile, vinyl zinc

bromide (prepared from vinyl magnesium bromide and zinc chloride), gave 1-allyl-3-

methyl-2,3-dihydro-1H-benzimidazole (2.28) in 83% yield. Compound 2.28 is extremely

sensitive to silica gel or neutral A1203; it was finally purified by flash column

chromatography on basic A1203. It also easily decomposes in CDC13 with disappearance

of the NCH2N methylene group, so NMR analysis was performed in DMSO-d6.

Treatment of 2.27 with 2 equiv of NaCN produced 94% yield of 2-(3-methyl-2,3-