Additions — Organocuprates

Like other carbon-carbon bond forming reactions organocuprate addition to enones is a powerful tool m organic synthesis... 

AUcyl transfer from the magnesium hahde to the chiral Cu complexes generates the Cu complex A, as deduced from NMR experiments. Very likely, this complex functions in a similar manner as previously postulated for organocuprate additions . 

In this concluding section, we will recall that a-selanylvinylmetal derivatives can be produced by a-deprotonation of vinylic aryl selenides 11, cleavage of ketene selenoacetals 12 or bromine/lithium exchange of a-bromovinyl selenides 13 (Scheme 49). These strategies involve vinylic selenides whose syntheses are not simple. More recent works have used organocuprate additions, hydrometala-tions (M = Sn, Zr) or hydroborations of readily available acetylenic selenides 14 (Scheme 49). The process can be regio- and stereocontrolled and produce the a-selanylvinylmetal derivatives under mild conditions. The latter can be considered as vinyl dianion equivalents and are very useful intermediates for cross-coupling reactions. 

The CpRe-Lewis acid shown in Sch. 25 forms stable complexes with cyclohexenone and cyclopentenone. The enones coordinate to the metal forming an Re-O cr-bond. Addition of organocuprates followed by treatment with HI yield enantiomerically enriched 3-alkylated cycloalkanones and an optically active Re-I complex. MeMgBr-ether and MeLi-ether gave low yields in these reactions. The data shown in Sch. 25 reflect the problem that the yields and enantioselectivity of the organocuprate additions vary widely with the reaction conditions used and the preparation of the organocuprate [122], and must be optimized for every reaction. 

JR)- and (S)-binaphthols 1.44 [230-235] have sometimes been used as chiral auxiliaries. Examples include reduction of y-ketoester 1.45 [236], nucleophilic substitution of binaphthol ethers (G = binaphthol) 1.46, by organomagnesium reagents, organocuprate additions to binaphthol monodnnamates [237], and alkylations of arylacetic or crotonic esters [238,239]. 

Heterocycles. A route to 2,3-disubstituted furans takes advantage of the Cu-Zn-transmetallation (with ZnCl2) from enolates derived from conjugate organocuprate addition to enones, and aldol reaction of zinc enolates to an alkoxyacetaldehyde. ... 

Most of the organocuprate -addition-a-alkylations of cyclopent-l-enones and cyclohex-2-enones have involved introduction of the nucleophilic -substituent and the electrophilic a-substituent preferentially in a trans-configuration. In contrast lithium diphenylcuprate addition to cyclopent-2-enone followed by a-alkylation involves attachment of the two new groups stereoselectively in a cis-relationship, even though such c/s-2-alkyl-3-phenylcyclopentanones are less stable than their trans-epimers [equation (14)]. ... 

The potential utility of organocuprate additions to aziridines for the preparation of secondary amines has already been noted above (Scheme 6), as was the general applicability of amlnomercura-tion reactions. Borohydride-mediated reductive alkylations of B-anilinomercurials have been used to obtain 1,5-functionalised... 

A new variation on an established route to the prostaglandins makes use of (80) to trap the product of organocuprate addition to the enone (79). ... 

Scheme 3.52 Internal delivery of organocuprate addition in hydroazulene synthesis.

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