Access to Aromatic Ring-Fused Benzimidazoles Using Photochemical Substitutions of the Benzimidazol-2-yl Radical

O’Connell, Joanne M.; Moriarty, Eoin; Aldabbagh, Fawaz

doi:10.1055/s-0032-1316775

Cited by 20 publications

(4 citation statements)

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“… 25 The photochemistry of 2-iodo-substituted BzIm yields aromatic ring-fused benzimidazoles via substitutions of the benzimidazol-2-yl radical. 26 The latter finding agrees with the report of Cole et al , 24 who found that 2-alkylbenzimidazoles do not give dimers but produce a mixture of acyl derivatives. N1-protonated benzopyrazoles 27 , 28 and benzisothiazoles were found to undergo isomerizations to the corresponding benzimidazoles and benzothiazoles ( Scheme 1 a).…”

Section: Introductionsupporting

confidence: 89%

“… 30 − 32 Interestingly, photoisomerizations opposite to those shown in Scheme 1 have not been reported. Although some reports about the photochemistry of benzimidazole in condensed media have already been published, 24 − 26 , 33 to the best of our knowledge, there are no reports on its photoinduced unimolecular transformations.…”

Section: Introductionmentioning

confidence: 99%

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Dual Photochemistry of Benzimidazole

et al. 2023

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Monomers of benzimidazole trapped in an argon matrix at 15 K were characterized by vibrational spectroscopy and identified as 1H-tautomers exclusively. The photochemistry of matrix-isolated 1H-benzimidazole was induced by excitations with a frequency-tunable narrowband UV light and followed spectroscopically. Hitherto unobserved photoproducts were identified as 4H- and 6H-tautomers. Simultaneously, a family of photoproducts bearing the isocyano moiety was identified. Thereby, the photochemistry of benzimidazole was hypothesized to follow two reaction pathways: the fixed-ring and the ring-opening isomerizations. The former reaction channel results in the cleavage of the NH bond and formation of a benzimidazolyl radical and an H-atom. The latter reaction channel involves the cleavage of the five-membered ring and concomitant shift of the H-atom from the CH bond of the imidazole moiety to the neighboring NH group, leading to 2-isocyanoaniline and subsequently to the isocyanoanilinyl radical. The mechanistic analysis of the observed photochemistry suggests that detached H-atoms, in both cases, recombine with the benzimidazolyl or isocyanoanilinyl radicals, predominantly at the positions with the largest spin density (revealed using the natural bond analysis computations). The photochemistry of benzimidazole therefore occupies an intermediate position between the earlier studied prototype cases of indole and benzoxazole, which exhibit exclusively the fixed-ring and the ring-opening photochemistries, respectively.

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Section: Introductionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Dual Photochemistry of Benzimidazole

et al. 2023

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“…Diastereoselectivity was not measured in the present UV-initiated reactions, but spectroscopic data for cycloadducts 3a , 3d and 3e (isolated in 17%–23% yield) matched the literature [5]. Aryl radical reduction products presumably formed by hydrogen abstraction from the solvent (acetonitrile [22,23,24]) were also detected, but not isolated and quantified. Yields of ( E )-3-ylideneoxindole acetates 2a and 2d – 2e were improved (55%–72%) when the acetonitrile reaction solvent was replaced by methanol (Scheme 3), which may partly be due to the absence of aryl radical reduction from the solvent.…”

Section: Resultssupporting

confidence: 62%

“…As part of this collaboration we became interested in forming the oxindole skeleton in the absence of toxic and hazardous radical initiators or expensive metal catalysts [22,23,24]. In this article, an “initiator and metal-free” photochemical radical pathway giving non-reduced adducts, ( E )-3-ylidene- oxindoles, after 5- exo - trig cyclization is reported (Scheme 3 and Scheme 4).…”

Section: Introductionmentioning

confidence: 99%