Synthesis of Indolo[1,2-a][1,8]naphthyridines by Rhodium(III)-Catalyzed Dehydrogenative Coupling via Rollover Cyclometalation

Abstract

The rhodium-catalyzed dehydrogenative coupling of N-pyridylindoles with alkynes proceeds smoothly through rollover cyclometalation to produce indolo[1,2-a][1,8]naphthyridine derivatives. A number of tetra-, penta-, and hexacyclic N-containing heteroaromatics can also be readily constructed in a similar manner. The L-shaped π-conjugated molecules exhibit intense solid-state fluorescence.

Switching of Reaction Pathway from C−C Rollover to C−N Ring‐Extension Annulation

“…N ‐pyridylbenzimidazole 1 a was successfully transformed to the C−C coupled product not only with diarylalkynes but also with dialkylalkynes in good yields ( 3 a – c , 63–80 %). It is important to note that only one specific example of the reaction of 1 a with diphenylacetylene producing 3 a was reported earlier ,. However, in this current work, this protocol has not only been generalized for the N ‐pyridylimidazole class of substrates, but a mechanistic rationale and viewpoint has also been provided.…”

A comprehensive overview of directing groups applied in metal-catalysed C–H functionalisation chemistry

“…While the rollover mechanism is more common for doubly coordinating ligands, such as bipyridines, 700 or in the case of a pyridine–carbene moiety like the one in Scheme 115E , 701 its occurrence is far less common in other substrates ( e.g. indole substrate in Scheme 115E ), 702 and is obviously facilitated by the absence of a non-coordinating anion in the reaction mixture.…”

Regioselective Direct C‐Alkenylation of Indoles

“…The two distinct modes of activation portrayed in Scheme for the hydroindolation reaction can be combined in a tandem process involving the N‐ (2‐pyridyl) unit for the synthesis of indolonaphthyridines (Scheme ) . The overall reaction is catalyzed by a Rh III complex while AgOAc is used as terminal oxidant for the last step.…”

“…The two distinct modes of activation portrayed in Scheme 28 for the hydroindolation reaction can be combined in at andem process involving the N-(2-pyridyl) unit for the synthesis of indolonaphthyridines (Scheme 59). [129] The overall reactioni sc atalyzed by aR h III complex while AgOAc is used as terminal oxidant for the last step. The procedure is rather versatile since the pyridyl moiety can be substituted by the quinoline system and furthermore is effective for al arge variety of symmetrical alkynes.Asingle example of unsymmetrical alkyne tested gave a3 :2 mixture of the corresponding regioisomers.…”