2-Cyclohexenone organocuprates

When organocuprates are added either to 4-substituted cydopentenones 1, or to 4-substituted or 5-substituted cyclohexenones (4 and 7), the trans addition product is generally obtained with good to excellent levels of diastereoselectivity (Scheme 6.1) [2-4]. The 6-substituted cydohexenone 10, however, predominantly gave the syn addition product [5, 6j. 

Scheme 6.6. Diastereoselectivity in conjugate additions of organocuprates to chiral bicyclic cyclohexenones (TMS = trimethylsilyl).

In the reaction of 2-cyclohexenone and of 4-phenylbut-3-en-2-one with chiral organocuprates of type (205), optical yields of only 5% and 15%, respectively, were obtained201 . Methylation of l,3-diphenyl-2-propene-l-one with (205) (R = CH3) produced (S)-l,3-diphenyl- 1-butanone in 68% enantiomeric excess 202>. 

Hydrindanediones. Conjugate addition of an organocuprate to a 4,4-di-substituted cyclohexenone is not stereospedflc, but steric control can be achieved indirectly by conjugate addition to enone lactones such as 1 for construction of either cis- or /rans-hydrindanediones such as 6. ... 

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. 

Table 8.22. Asymmetric Induction in Conjugate Addition of Organocuprates Containing Chiral Ligands to Cyclohexenone...

Cyclohexenones. Interest has been maintained in the use of lithium organocuprates... 

While several NMR spectroscopic studies have established the involvement of Jt- and -complexes in CA of organocuprates, littie evidence was obtained for the carbocupration pathway until the early 2000s, when experimental evidence supporting a carbocuprate-Uke intermediate was reported. Reacting cyclohexenone 1 with customised homocuprate 74 bearing an enolate moiety in its structure afforded bicyclic alcohol 75 as major product (Scheme 28) [120]. The formation of 75 is more consistent with a mechanism involving carbocupration intermediate... 

Scheme 28 Experimental observation for carbocuration meebanism in CA of organocuprate 74 to cyclohexenone 1...

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