Condensation of methylcrotonic acid with 4-chloro-o-phenylenediamine in 4N HCl yielded 5-chloro-2-(1-isobutenyl)benzimidazole and 7-chloro-4, 4-dimethyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one. Methacrylic acid when condensed with o-phenylenediamine in 4N HCl yielded the already reported 3-methyl-1,2,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one and 2(2-propenyl)benzimidazole. Condensation of methacrylic acid with 4-chloro-o-phenylenediamine in 4N HCl yielded 5-chloro-2(2-propenyl)benzimidazole. The structures of all the purified compounds were confirmed with the help of mass and $^1$H NMR spectral analysis.
HASAN, Mashooda; MUNAWAR, Shagufta; KHAN, Naeema; and MAQBOOL, Zahida (1998) "Further Studies on the Reaction of Unsaturated Acids with o-Phenylenediamine and 4-Substituted o-Phenylenediamines in Acid Medium," Turkish Journal of Chemistry: Vol. 22: No. 4, Article 8. Available at: https://journals.tubitak.gov.tr/chem/vol22/iss4/8