Palladium(II)‐Catalyzed Regioselective Direct C2 Alkenylation of Indoles and Pyrroles Assisted by the N‐(2‐Pyridyl)sulfonyl Protecting Group

Abstract

Leicht hin, leicht weg: In Gegenwart der N‐(2‐Pyridyl)sulfonylgruppe gelingt die direkte PdII‐katalysierte Alkenylierung von Indolen an C2 in guten Ausbeuten (siehe Schema, DMA=Dimethylacetamid). Das Protokoll wurde auf Pyrrolderivate erweitert. Eine anschließende reduktive Desulfonylierung lieferte die C2‐substituierten Indole und Pyrrole ebenfalls in guten Ausbeuten.

Removable Directing Groups in Organic Synthesis and Catalysis

“…[10] The role of the (2pyridyl)sulfonyl group has been explored by changing the nature of the N-indole substituent. [10] The role of the (2pyridyl)sulfonyl group has been explored by changing the nature of the N-indole substituent.…”

“…The (2-pyridyl)sulfonyl group has been used as a protecting and directing group by Carretero and co-workers to achieve an efficient and general palladium-catalyzed C2alkenylation of indoles and pyrroles. [10] The role of the (2pyridyl)sulfonyl group has been explored by changing the nature of the N-indole substituent. Thus, alkenylation occurred regioselectively in 75 % yield at position 3 in the case of the unsubstituted indole (Table 1, entry 1).…”

Rh(III)-Catalyzed, Highly Selectively Direct C–H Alkylation of Indoles with Diazo Compounds

“…Nevertheless, compared with C3-H functionalization, the methods that allow for the C2-H functionalization of indoles are still rare due to the weak reactivity of the C-H bond at the C2-position of an indole [13,14]. In this context, some excellent studies on selective arylation [15], alkenylation [16], alkynylation [17], cyanation [18], and acylation [19] of the C2-H bond of indoles have been conducted. However, the methods that allow for direct C2-H alkylation of indoles are still rare.…”

Ruthenium(II)‐Catalyzed CH Alkenylations of Phenols with Removable Directing Groups

“…[1] In particular, ruthenium(II) complexes [2] have very recently been identified as versatile catalysts for double CÀH bond functionalizations with arenes bearing a diverse set of Lewis-basic directing groups. [3,4] However, despite these recent advances, ruthenium-catalyzed oxidative alkenylations of arenes arguably continue to be limited in that methods that exploit removable directing groups [5][6][7] are scarce. Given our recent success in the use of a removable directing group in the direct arylation with aryl halides as prefunctionalized arylating reagents, [8] we consequently became attracted to devising a novel ruthenium-catalyzed oxidative alkenylation of phenols displaying removable directing groups.…”