Rh(III)-Catalyzed C–H Bond Activation along with “Rollover” for the Synthesis of 4-Azafluorenes

Abstract

An intramolecular reaction of 3-alkynyl and 3-alkenyl-2-arylpyridines selectively gave 4-azafluorene compounds in the presence of a catalytic amount of [Cp*RhCl(2)](2) and Cu(OAc)(2). Pyridine-directed C-H bond activation along with "rollover" are likely to be key steps of this transformation.

Recent Advances in [Cp*MIII] (M = Co, Rh, Ir)‐Catalyzed Intramolecular Annulation Through C–H Activation

“…Following this strategy, more sophisticated scaffolds, such as multiple fused rings can be obtained. Shibata et al showed that [Cp*RhCl 2 ] 2 is a suitable catalyst to access 4‐azafluorene from 3‐alkenyl‐2‐arylpyridines 22a – b (Scheme ) . Intermediate C is obtained after coordination of the Rh III onto the pyridine directing group of 22a – b followed by subsequent C–H activation.…”

1,3-Dien-5-ynes: Versatile Building Blocks for the Synthesis of Carbo- and Heterocycles

“…175 Thus, cyclization of 3-alkynyl-2-arylpyridines in the presence of catalytic amounts of [Cp*RhCl 2 ] 2 and Cu(OAc) 2 leads to 4-azamethylenefluorene derivatives in moderate to good yields and generally low diastereoselectivities (Scheme 77, eq. 1).…”

Palladium(II)‐Catalyzed Tandem Synthesis of Acenes Using Carboxylic Acids as Traceless Directing Groups

“…[11,12] We were intrigued by the possibility of atandem transformation employing removable carboxylic acid directing groups,which simultaneously afforded catalytic control and efficiency.I np articular,w es peculated that the olefinated intermediate generated in situ as ar esult of the Pd(II)-catalyzed, carboxyl-directed alkenylation of ad iaryl carboxylic acid, could be further utilized for another C-H activation in the context of the same directing group.T he sequential C-H functionalization approach is ah ighly efficient method for intramolecular cyclization of diaryl compounds. [13] Subsequently,wehypothesized that rollover of the palladated intermediate might enable coordination to an alkene moiety, [14] which would set the stage for intramolecular C À Cbond formation. Finally,the carboxylate group could be removed in atraceless fashion by decarboxylative aromatization, affording the desired anthracene products.Ifsuccessful, this strategy represents an ovel approach to step-economical synthesis of diversely functionalized anthracene and heteroacene derivatives (Scheme 1).…”

“…In particular, we speculated that the olefinated intermediate generated in situ as a result of the Pd(II)-catalyzed, carboxyl-directed alkenylation of a diaryl carboxylic acid, could be further utilized for another C-H activation in the context of the same directing group. The sequential C-H functionalization approach is a highly efficient method for intramolecular cyclization of diaryl compounds.[13] Subsequently, we hypothesized that rollover of the palladated intermediate might enable coordination to an alkene moiety, [14] which would set the stage for intramolecular C À C bond formation. Finally, the carboxylate group could be removed in a traceless fashion by decarboxylative aromatization, affording the desired anthracene products.…”