2295-42-3Relevant academic research and scientific papers
Regiodivergent Cross-Dehydrogenative Coupling of Pyridines and Benzoxazoles: Discovery of Organic Halides as Regio-Switching Oxidants
Yamada, Shuya,Murakami, Kei,Itami, Kenichiro
supporting information, p. 2415 - 2418 (2016/06/09)
Cross-dehydrogenative coupling (CDC) of two unfunctionalized heteroarenes has been recognized as an ideal transformation to synthesize privileged heterobiaryl scaffolds. However, regioselective activation and transformation of a specific set of two heterocyclic C-H bonds among other bonds have been extremely challenging. Thus, discovering a new controlling element to achieve regio-controlled and regio-divergent heterocyclic CDCs is considered crucial. In this Letter, the unprecedented use of organic halides as an oxidant to achieve the CDC reaction of pyridines and benzoxazoles with palladium catalyst is described. Moreover, the regioselectivity of the pyridine functionalization site can be controlled by the choice of organic halides.
Synthesis of 2-pyridinylbenzoxazole: Mechanism for the intramolecular photosubstitution of the haloarene with the carbonyl oxygen of the amide bond in basic medium
Park, Yong-Tae,Jung, Chang-Hee,Kim, Kwang-Wook,Kim, Ho Sik
, p. 8546 - 8556 (2007/10/03)
2-Pyridinylbenzoxazole derivatives have been synthesized by the intramolecular photosubstitution reaction of N-(2- halophenyl)pyridinecarboxamide (1 and 2) with its amide bond in basic medium. In neutral medium both intramolecular photosubstitution and photoreduction reactions occurred. In the photosubstitution reaction a singlet state of the o-haloarene is involved, whereas in the photoreduction a triplet state of the o-haloarene is involved; oxygen inhibited the photoreduction but not the photosubstitution. The relative rate studies showed that a base accelerates the photosubstitution reaction but decelerates the photoreduction. o- Iodoarenecarboxamide is more reactive than o-bromoarenecarboxamide, which in turn is more reacitive than o-chloroarenecarboxamide. UV-vis absorption change in the presence of a base showed that an imidol and/or imidolate anion is involved in the reaction. Several transient species, such as charge- transfer excited states and a cyclohexadienyl anion radical, have been identified from the photolysis of 1 and 2 in basic medium by laser flash photolysis. In neutral medium dibromide anion radical and a phenyl radical were identified in addition to the above intermediates. On the basis of the photokinetic and laser flash photolysis studies, an intramolecular photosubstitution of N-(o-halophenyl)pyridinecarboxamide with its amide bond occurs via an intramolecular S(N)(ET)Ar* mechanism to afford 2- pyridinylbenzoxazole derivative, and the photoreduction proceeds via a free radical mechanism to give N-phenylpyridinecarboxamide.
