Organozinc reagents primary alkyl

Organozinc reagents have been used in conjunction with a-bromovinylboranes in a tandem route to Z-trisubstituted allylic alcohols. After preparation of the vinylborane, reaction with diethylzinc effects migration of a boron substituent with inversion of configuration and exchange of zinc for boron.176 Addition of an aldehyde then gives the allylic alcohol. The reaction is applicable to formaldehyde alkyl and aryl aldehydes and to methyl, primary, and secondary boranes. 

Nickel acetylacetonate, Ni(acac)2, in the presence of a styrene derivative promotes coupling of primary alkyl iodides with organozinc reagents. The added styrene serves to stabilize the active catalytic species, and of the derivatives examined, m-trifluoromethylstyrene was the best.274... 

Aryl and alkyl organozincate reagents, generated in situ by reaction of Grignard reagents and sub-stoichiometric amounts of ZnCl2, cross-couple smoothly in refluxing THF with functionalized aryl and alkenyl as well as primary and secondary alkyl chlorides in the presence of Pd(dppf)Cl2. ... 

The high chemoselectivity of organozinc reagents also allowed the use of the functionalized secondary a-acetoxy alkyl bromide 50 which was converted to 34a (equation 19)36, a product previously obtained by the cyclization of a 5-ethylenic primary iodide bearing the acetoxy group at the allylic position (equation 13). 

The scope of the Negishi reaction is broad, similar to that of Stille and Suzuki cross-coupling. The reaction seems to work if R = aryl, vinyl, alkynyl, acyl, allyl, benzyl, homoallyl (-CH2-CH2-CH=CH2) and homobenzyl (-CH2-CH2-Ph), or even primary alkyl, and if X = I, Br, or OTf (Cl works, but often sluggishly). Correspondingly, R = aryl, vinyl, alkynyl, allyl, benzyl, and primary alkyl. The organozinc reagent may either be used as a preformed compound, such as R2Zn... 

Secondary alkyl bromides are sufficiently reactive under these conditions, but primary alkyl bromides are usually inert and much better results are obtained by using highly activated Rieke-zinc. Thus, the reduction of zinc chloride with lithium naphthalenide, freshly prepared from finely cut lithium and naphthalene in THF, produces within 1.5 h highly reactive zinc (Rieke-zinc). This form of zinc readily reacts with secondary and tertiary alkyl bromides. Adamantyl bromide (217) was converted into the corresponding organozinc reagent 218. Its reaction with cyclohexenone in the presence of BF3 OEt2 and TMSCl afforded the 1,4-addition product 219 in 54% yield (Scheme 2-87). 

The addition of Lil and LiBr mixtures allows also the performance of the zinc insertion with primary alkyl chlorides, tosylates or mesylates as starting material. Thus, the alkyl tosylate like 239 can be converted in A. A -dimethylacetamide (DMAC) in the presence of lithium iodide (0.2 equiv.) and lithium bromide (1.0 equiv.) after heating at 50 °C for 12 h into the organozinc reagent 240 and reacted with various electrophiles like 3-iodo 2-cyclohexenone leading to the cyclohexenone 241 in 85% yield (Scheme... 

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