Coupling reactions of organocuprates

Scheme 8.1 gives several examples of the use of coupling reactions of organocuprate reagents with halides and acetates. Entries 1 to 3 are examples of the... 

Alkanes can also be prepared from alkyl halides by reduction, directly with Zn and acetic acid (AcOH) (see Section 5.7.14) or via the Grignard reagent formation followed by hydrolytic work-up (see Section 5.7.15). The coupling reaction of alkyl halides with Gilman reagent (R 2CuLi, lithium organocuprates) also produces alkanes (see Section 5.5.2). 

Inconsistent with both of the above mechanistic proposals is the recent finding that secondary iodides, unlike bromides and sulfonates, undergo nearly complete racemization in coupling reactions with organocuprates. In addition, bicyclic compounds are produced in reactions of 6-iodocyclooctene with... 

Aromatic iodides may be converted into thiophenols by nickel(O)-catalysed reductive coupling with thiourea followed by alkaline treatment of the intermediate salt and liberation of the desired product on acidif ication. Reaction of organocuprates with... 

Table 9.2 Cross-coupling reactions of calcium organocuprate reagents with benzoyl chloride.°...

The most frequently used organocuprates are those m which the alkyl group is pri mary Steric hindrance makes secondary and tertiary dialkylcuprates less reactive and they tend to decompose before they react with the alkyl halide The reaction of cuprate reagents with alkyl halides follows the usual 8 2 order CH3 > primary > secondary > tertiary and I > Br > Cl > F p Toluenesulfonates are somewhat more reactive than halides Because the alkyl halide and dialkylcuprate reagent should both be primary m order to produce satisfactory yields of coupled products the reaction is limited to the formation of RCH2—CH2R and RCH2—CH3 bonds m alkanes... 

Propiolaldehyde diethyl acetal has found numerous synthetic applications in the literature which may be briefly summarized. The compound has been utilized in the synthesis of unsaturated and polyunsaturated acetals and aldehydes by alkylation of metal-lated derivatives, " by Cadiot-Chodkiewicz coupling with halo acetylenes, " and by reaction with organocuprates. Syntheses of heterocyclic compounds including pyrazoles, isoxazoles, triazoles, and pyrimidines have employed this three-carbon building block. Propiolaldehyde diethyl acetal has also been put to use in the synthesis of such natural products as polyacetylenes " and steroids. ... 

Coupling with enol esters (7, 93). A new synthesis of an alkyl-substituted alkene involves coupling of a lithium dialkyl cuprate with an enol triflate,1 available from a ketone by reaction with triflic anhydride and 2,6-di-t-butylpyridine.2 A wide variety of organocuprates can be used and the geometry of the enolate is largely retained. Reported yields are in the range 60 100%. 

Likewise, the reaction of iodonium salt 57 with lithium organocuprate reagents affords products of coupling 65 in good yields (Scheme 30) [54]. 

The synthetic potential of coupling reactions between vinyliodonium salts and organocuprates has not been exploited. However, some indication of their promise is provided by reported syntheses of bicyclic enediynes in the norbornadiene and 7-oxanor-bornadiene series from the appropriate bisiodonium triflates and lithium dialkynyl-cuprates (equation 221)148. 

Predict the coupling products of the organocuprate, Heck, and Suzuki reactions, and use these reactions in syntheses. Problems 17-49, 55, 65, and 68... 

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