Zinc-copper organometallics

SCHEME 85. Cross-couphng of zinc-copper organometallics with 1-haloalkynes... 

Ziegeler-Natta conditions 304 zig zag chromophores 217 zinc-copper exchange 275 zinc-copper organometallics 397 zinc-copper reagents 396, 397 reactions with acid chlorides 398 zinc-copper species RCu(CN)ZnX 394 zinc enolates 20 zinc metal, activated 291 zinc organometallics 278, 389 zinc salts 9... 

The cross-coupling reaction with non-activated iodoalkenes proceeds well only by using a polar solvent like NMP or DMPU [29] and elevated reaction temperatures (60 °C, 12 h). The compatibility of the zinc-copper reagents with these harsh reaction conditions shows the remarkable thermal stability of zinc-copper organometallics. The cross-coupling reaction occurs with complete retention of the configuration of the double bond and allows the stereospecific synthesis of highly functionalized alkenes like 29 (see Section 9.6.6 Scheme 9-27) [57],... 

ADDITION OF A FUNCTIONALIZED ZINC-COPPER ORGANOMETALLIC RCu(CN)Znl] TO AN a.p-UNSATURATED ALDEHYDE (E)-2-(4-HYDROXY-6-PHENYL-5-HEXENYL)-1 H-ISOINDOLE-1,3(2H)-DIONE (1 H-lsolndole-1,3(2H)-dione, 2-(4-hydroxy-6-phenyl-5-hexenyl)-)... 

Substitution reactions of zinc or zinc-copper organometallics with RaSiCl are usually difficult, whereas tin reagents of t3T>e RsSnCl react more eflBciently. Thus, the -zincated phosphonate 347 provides imder mild conditions the stannylated product 348 in 81% yield " (Scheme 2-118). 

Alkynyl iodides and bromides smoothly react with various zinc-copper organometallics at -60 C leading to polyfunctional alkynes [48dj. lodoalkynes, such as 296 [188] react at very low temperature, but lead in some cases to copper acetylides as byproducts (I/Cu-exchange reaction). 1-Bromoalkynes are the preferred substrates. Corey and Helel have prepared a key intermediate 297 of the side chain of... 

A convenient method for the conversion of aldehydes (RCHO) to alkenes (RCH = CHj), knovm as methylenation, involves the reaction of a zinc/copper couple with diiodomethane in the presence of the carbonyl compound dissolved in tetrahy-drofuran. The reaction first generates an organometallic intermediate (ICH2ZnI) which then reacts with the carbonyl compound. The conversion of benzaldehyde to styrene using this conventional methodology required a reaction time of 6 h at 40 °C. When the reaction was sonicated however comparable yields of around 70%... 

Diethylzinc, one of the first organometallic compounds to be isolated (Fran-kland, 1849), epitomizes these characteristics. The compound is easily prepared by heating powdered zinc or zinc-copper alloy with ethyl iodide under an atmosphere of dry nitrogen or CO2 (the initial product is actually C2H5ZnI, which disproportionates on distillation to zinc iodide and diethylzinc) ... 

The same group2 now finds that a zinc/copper couple prepared by sonication of Zn and Cul in ethanol/H20 (9 1) permits conjugate addition of alkyl halides to enones and enals. The order of reactivity is RI > RBr and tert > sec primary. THF/H20 or Py/HzO or even pure water can be used as solvent. This reaction can hardly involve a classical organometallic reagent, but probably involves an alkyl radical. 

Addition of a Functionalized Zinc and Copper Organometallic (RCu(CN)Znl) to an a.p-Unsaturated Aldehyde. 

A similar insertion of zinc with aryl iodides requires N,N-dimethylformamide or -acetamide as solvent. These arylzinc iodides react with CuCN-2LiCl to form mixed zinc and copper organometallics, ArCu(CN)ZnI, which react with a variety of electrophiles to give functionalized aromatics.4... 

Amino acid synthons can be prepared from iodoalanine with no loss of optical integrity (Scheme 48). The amino acid was transformed into a novel zinc reagent through reductive metallation with a zinc-copper couple in benzene/dimethyl acetamide. This organometallic was acylated under palladium catalysis in good overall yield. ... 

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