Rhodium-Catalyzed One-Pot Access to N-Polycyclic Aromatic Hydrocarbons from Aryl Ketones through Triple C–H Bond Activations

Abstract

A Rh-catalyzed pot and step economic synthesis of aza-polycyclic aromatic hydrocarbons (N-PAHs) from readily available aryl ketones and alkynes has been disclosed. Additionally, a novel synthetic application of the well-known aminating reagent hydroxylamine-O-sulfonic acid (HOSA) has been explored as an in situ redox-neutral directing group for the formation of N-PAHs via isoquinoline. Multiple bond formation in a single operation through a cascade of triple C−H bond activations is the beauty of this protocol. The challenging annulations of two different alkynes in a regioselective fashion have been demonstrated effectively. Mechanistic studies reveal that 3,4-diphenyl-1-methylisoquinoline is an active intermediate for this one-pot transformation.

Synthesis of substituted (N,C) and (N,C,C) Au(iii) complexes: the influence of sterics and electronics on cyclometalation reactions

“…The N1–C1–C13 angle (120.9(3)°) in 6-methyl-substituted 2i-Au(OAc F ) 2 is slightly larger than the corresponding N–C–C(alkyl) angles in reported crystal structures of non-coordinated pyridines, bipyridines or phenanthrolines with alkyl substituents α to nitrogen (typically around 115°). 89–93 This indicates that Au( iii ) coordination to 6-methyl-substituted pyridines results in a widening of the N–C–C(methyl) angle, contrary to the effect Au( iii ) coordination has on the N–C–O(methoxy) angle in 6-methoxy-substituted pyridines. The N–C–C(alkyl) angle in 2i-Au(OAc F ) 2 is similar to reported angles for related square planar Au( iii ) 94 and Pd( ii ) 58 complexes of 6-methyl-substituted (bi)pyridine ligands.…”

Diverse reactivity of alkynes in C–H activation reactions

“…Following their work on the application of hydroxylamine- O -sulfonic acid to form isoquinolines, Ravikumar et al recently reported the synthesis of aza-polycyclic aromatic hydrocarbons 62 via triple C–H bond activation of aryl ketones 61 and internal alkynes 63 (Scheme 22). 33 This Rh( iii )-catalysed transformation also demonstrated the annulation of two different alkynes in a regioselective manner. The substrate scope for this reaction was generalised with a wide range of substituents.…”

Reactivity of Alkynes with M-C Bonds generated through C-H Activation

“…The scope of benzophenones was also vast, and most of the substitutions were tolerated successfully. 33 This Rh(III)-catalyzed transformation also demonstrated the annulation of two different alkynes in a regioselective manner. The substrate scope for this reaction was generalized with a wide range of substituents.…”