Palladium catalyzed/norbornene-mediated

Fused pyrazole compounds have been prepared from A-alkyl substituted pyrazoles. For example, a palladium-catalyzed/norbornene-mediated sequential coupling reaction involving an aromatic sp2 C-H functionalization as the key step has been described, in which an alkyl-aryl bond and an aryl-heteroaryl bond were formed in one pot <060L2043>. A variety of highly substituted six-membered annulated pyrazoles 59 were synthesized in a one-step process in moderate yields from IV-bromoalkyl pyrazoles 57 and aryl iodides 58. 

A variety of substituted seven-membered annulated pyrroles can be synthesized in a one-step process in good yields from readily accessible N-bromoalkyl pyrroles 75 and aryl iodides. The synthesis is based on a palladium-catalyzed/ norbornene-mediated sequential coupling reaction involving an aromatic sp C-H functionalization as the key step. The proposed mechanism suggests that orffzo-alkylation with the formation of intermediate 76 most likely precedes aryl-heteroaryl coupling (Scheme 15 (20060L2043)). 

Palladium-Catalyzed/Norbornene-Mediated ortho C-H Activations... 

A series of reports from the Lautens group and others have described the synthesis of phenanthridines, an important class of compounds with a broad range of biological activities, utilizing palladium-catalyzed/norbornene-mediated... 

Prior to his work on pyrrole C—H activation, Bach applied his palladium-catalyzed norbornene-mediated methodology to the indole ring system (Scheme... 

SCHEME 22.50 Palladium-catalyzed norbornene-mediated annulation of iodoarenes and 2-haloarylaldehydes, ketones, and esters. 

This palladium-catalyzed coupling mediated by norbornene has also been conducted with aryl halides containing an ortho substituent in the presence of a coupling partner, such as cyanide (Equation 19.155). In this case, tihe product does not contain the nor-bomene additive. Various coupling partners include cyanide, olefins, allylic alcohols, diphenyl- and alkylphenylacetylenes, arylboronic acids, hydrogen donors, and amides. The proposed mechanism (Scheme 19.20) begins with the oxidative addition of Pd(0)... 

Figure 8.2 Selectively substituted bi- and teraryls accessible by norbornene-mediated palladium-catalyzed multicomponent reactions [362].

Figure 8.3 Selectively substituted heteroatom-containing bicyclic, tricyclic, and higher oligo-cyclic systems assembled in norbornene-mediated palladium-catalyzed cascade reactions [363-366].

A norbornene-mediated, palladium-catalyzed sequence was described to form annulated indoles (eq 155). Furans or thiophenes can undergo a similar cycUzation to provide annulated... 

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