Alkyl iron-catalyzed arylations

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. 

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

Iron-Catalyzed Arylations of Alkyl (Pseudo)Halides... 

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...

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

Iron-catalyzed Suzuki-Miyaura coupling reactions were also reported by Nakamura and colleagues (entry 27) [67]. Alkyl halides 1 and mixed pinacol aryl(butyl)borates, generated in situ from arylboronates and butyllithium, were used as the reagents and 10 mol% of the iron complexes 16a or 16b as the catalysts. The addition of 20 mol% of MgBr2 was essential for the success of the reaction. Products 3 were isolated in 65-99% yield. The methodology tolerates ester and nitrile functions. The reaction starts probably by initial boron-iron transmetalation to generate a diaryliron(II) complex. 

In 2004, his group described in some detail the iron-catalyzed cross-couphngs of alkyl and aryl Grignards with enol triflates, acid chlorides, and dichloroarenes. Enol triflates give good to excellent yields many substrate fhnctional groups (e.g. esters, enones, carbamates) are tolerated, and several fhnctionahzed Grignards work well. 

Furstner, A., Leitner, A. Iron-catalyzed cross-coupling reactions of alkyl-Grignard reagents with aryl chlorides, tosylates, and triflates. Angewandte Chemie, International Edition 2002,41, 609-612. 

Palladium(ll)-catalyzed intramolecular stereoselective Irons alkoxycarbonylation of 4-alkyl- and 4-aryl-3-butyn-l-ols 7 gives /f-tetrasubstituted a-methylene-y-butyrolactones 8 if conducted in the presence of copper(II) chloride, methyloxirane and triethyl orthoacetate. In the absence of the copper salt, intramolecular dicarbonylation occurs (e.g., giving 9, see Section 1.5.8.3.3.). The latter reaction type is also observed if the alkyne moiety is substituted by a trimethylsilyl instead of an alkyl or aryl group60,61. 

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