Aryl iron-catalyzed

Our group has recently developed an alternative method for alkyl-(hetero)aryl- as well as aryl-heteroaryl cross coupling reactions catalyzed by iron salts.3 4 This methodology was inspired by early reports of Kochi et al.5>6 on iron-catalyzed cross coupling of vinyl halides and is distinguished by several notable advantages. 

Scheme 29 Iron-catalyzed cross coupling reaction of aryl Grignard reagents with alkyl halides...

Recent notable improvements by Knochel and co-workers include iron-catalyzed cross-coupling reactions of various acid chlorides 148 with dialkylzinc reagents (Equation (24))324 as well as the iron-catalyzed arylation of aroyl cyanides 149 with Grignard reagents (Equation (25)).3 5 In the first case Knochel s reaction conditions tolerate ester groups on the organozinc compounds, while in the latter case ester, aryl alkyl ether, cyano, and chloro functionalities on the aromatic moieties are compatibles with the reaction conditions. 

However, arylmagnesium organometaUics can only be used in a few cases " like an iron-catalyzed homocoupling (equation 92) . Iron catalysis is further used for the dechlorination of electron-rich aryl chlorides by Grignard reagents . ... 

B. Iron-catalyzed Arylation and Heteroarylation of Alkyl Grignard Reagents 610... 

C. Iron-catalyzed Heteroarylation of Aryl Grignard Reagents. 614... 

D. Iron-catalyzed Alkylation of Aryl Grignard Reagents. 615... 

In 1971, a year before the groups of Corriu and Kumada [5] independently reported the groundbreaking work on the topic of nickel-catalyzed cross-coupling reactions of aryl and vinyl halides with Grignard reagents, Tamura and Kochi described an iron-catalyzed vinylation reaction of Grignard reagents with vinyl halides (Scheme 5.1) [6]. 

Table 5.4 Reactivity profile of aryl electrophiles in iron-catalyzed cross-coupling reactions.

Table 5.5 Scope of aryl chlorides and sulfonates in iron-catalyzed cross-coupling reaction with RMgBr.

Table 5.6 Iron-catalyzed aryl-aryl coupling reaction developed by Knochel s group.

Scheme5.11 Iron-catalyzed aryl-aryl cross-coupling reaction with Ar-MgX developed by Hatakayama and Nakamura.

The first general iron-catalyzed arylation of benzyl alcohols and benzyl carboxylates was published by our group in 2005 [56]. A practical synthesis of a multitude of... 

Again FeCl3-6H20 is the catalyst of choice for the benzylation of o-xylene by 4-chlorostyrene (Table 6.2). This iron-catalyzed arylation reaction of styrenes allows the synthesis of a wide variety of 1,1-diarylalkanes employing various styrenes and diverse arenes. Scheme 6.15 illustrates selected examples of successfully synthesized 1,1-diarylalkanes and Table 6.3 shows the diversity of different substituted styrenes employed as benzylating agents. 

Recently, Taillefer et al. reported an Fe/Cu cooperative catalysis in the assembly of N-aryl heterocycles by C—N bond formation [90]. Similarly, Wakharkar and coworkers described the N-arylation of various amines with aryl halides in the presence of Cu—Fe hydrotalcite [91]. Interestingly, Correa and Bolm developed a novel and promising ligand-assisted iron-catalyzed N-arylation of nitrogen nucleophiles without any Cu co-catalysts (Scheme 6.19) [92]. Differently substituted aryl iodides and bromides react with various amides and N-heterocycles. The new catalyst system consists of a mixture of inexpensive FeCl3 and N,N -dimethylethylenediamine (dmeda). Clearly, this research established a useful starting point for numerous future applications of iron-catalyzed arylation reactions. 

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