Heck alkyl halides with styrenes

Fig. 62 Co(I)-catalyzed Heck reactions of alkyl halides with styrene...

Cobalt-catalyzed Heck-type Reaction of Alkyl Halides with Styrenes... 

A method complementary to the palladium-catalyzed reaction has been reported. A cobalt-phosphine complex catalyzes a Heck-type reaction of alkyl halides with styrenes in the presence of Me3SiCH2MgCl [174]. Trimethylsilylmethylmag-nesium chloride was added to a mixture of styrene and bromocyclohexane in ether in the presence of a catalytic amount of CoCl2(dpph) at O C. Heating the reaction mixture under reflux (35°C) provided 163a in 91% yield (Scheme 3.158). 

Scheme 2.24 Heck reaction between an alkyl halide and styrene with a Pd(0)catalystsupported...

A more efficient and more generahy applicable cobalt-catalysed Mizoroki-Heck-type reaction with aliphatic halides was elegantly developed by Oshima and coworkers. A catalytic system comprising C0CI2 (62), l,6-bis(diphenylphosphino)hexane (dpph 73)) and Mc3 SiCH2MgCl (74) allowed for intermolecular subshtution reactions of alkenes with primary, secondary and tertiary alkyl hahdes (Scheme 10.25) [51, 53]. The protocol was subsequently applied to a cobalt-catalysed synthesis of homocinnamyl alcohols starting from epoxides and styrene (2) [54]. 

An organometallic reaction which shows a close similarity to the Mizoroki-Heck reaction is the cobalt-catalysed [46] reaction between alkenes and organic halides. The use of [CoCKPPhsls] (59) as catalyst for intermolecular arylations of methyl acrylate (1) and styrene (2) was reported by Iyer [47] (Scheme 10.20). The para-substituted aryl iodides could be employed with this homogeneous catalyst, but the more sterically hindered ortho-substituted iodoarenes failed to undergo the desired substitution reaction. Aryl bromides and chlorides, as well as alkyl-substituted halides, proved unreactive under these reaction conditions. 

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