3-Substituted-2-pyridin-2-ylindoles

The regioselectivity of Larock indole annulation with 2-alkynylpyridines and o-iodoaniline to give 3-substituted-2-pyridin-2-ylindoles has also been rationalized by a combination of steric and electronic coordinative effects (2008TL363 Scheme 3). A coordination of the pyridine nitrogen during the catalytic cycle was postulated to justify the different regioisomeric ratios 94 6, 68 32, and 72 28 of the Larock reaction obtained with cyclopentyl 2-, 3- and 4-pyridyl acetylenes, respectively. 

Due to the importance of indole and pyridine moieties in natural products and pharmaceutical compounds, the cyclization between 2-iodoanilines with 2-all nylpyridines was developed in 2008. 3-Substituted-2-pyridin-2-ylindoles were produced in good yields in DMP at 140 °C with Pd(OAc)2 (5 mol%) as the catalyst, DPPF (7.5 mol%) as the ligand and KOAc as the base. However, the regioselectivity was rationalized by a combination of steric, coordinative and electronic effects. 

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See also in sourсe #XX -- [ ]

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