Organocuprates, higher order

Hydroxy stannanes can be prepared by cleavage of epoxides with BusSnLi or cleavage of epoxy stannanes with organocuprates (equation 33)72. The two methods are stere-ochemically complementary. The higher order cyanocuprate, Bu3Sn(Bu)Cu(CN)Li2, also affords /1-hydroxy stannanes by reaction with epoxides54. 

B.H. Lipshutz, Application of Higher-Order Mixed Organocuprates to Organic Synthesis, Synthesis 1987, 325, s.d.S.335ff. 

For reviews of these and other higher order organocuprates, see Lipshutz Wilhelm Kozlowski Tetrahedron 1984, 40, 5005-5038, Lipshutz Synthesis 1987, 325-341, Synlett 1990, 119-128. See also Bcrtz J. Am. Chem. Soc. 1990, 112. 4031 Lipshutz Sharma Ellsworth J. Am. Chem. Soc. 1990, 112. 4032. 

The direct nucleophilic acylation of enals by organocuprates is also successful.37-38 With either the lower order RCuCNLi/CO or higher order R2CuCNLi2/CO reagents, high yields of the 3-acylated pro duct were observed (equation 37). A wide variation in R was also reported to be tolerated. Unfortunately, only (3-monosubstituted enals were examined, so the extent to which substitution in the enal can be tolerated has yet to be determined. 

Secondly it has been found that a number of trialkylsilyl groups can be added stereoselectively to the /j-position of the C —C double bond in dioxanone 10 (derived from enantiomerically pure 3-hydroxybutanoic acid)23. In this case the presumed silylcuprate is generated from a chlorosilane and a higher-order organocuprate. In the example shown, with addition of phenyldimethylsilyl chloride, a diastereomeric ratio of 91 9 was obtained. Improved ratios were obtained with other groups (e g., 98 2 for trimethylsily 1), but unfortunately none of the latter were susceptible to oxidative cleavage. The first two steps of the procedure produce a mixture of 11 and its silyl enol ether, which is then desilylated to 11 by treatment with tetrabutylammonium fluoride. 

Finally, the carbometallation reaction of spirocyclic cyclopropenes with a chiral ketal attached to the substrate was described. Thus, carbocupration of the chiral cyclopropene 96 proceeded with 96% diastereoselectivity with a higher-order organocuprate [134] (Scheme 7-114). 

Double substitution of geminal dibromides is best accomplished by treatment with an organocuprate, followed by the addition of an alkyl iodide to the crude reaction mixture. " The reaction has found especial application for the synthesis of dimethylcyclopropanes, ubiquitous in natural product chemistry. Excellent yields are often obtained with Me2CuLi, but with less reactive substrates higher order cyano-and thiocyano-cuprates sometimes provide better results. Spiro dialkylation of geminal dibromides has also been accomplished. Vicinal dibromides, on the other hand, afford alkenes upon treatment with dialkyl cuprates. ... 

In contrast to their reaction with R R CuLi (R = alkyl, R = alkyl or CN), the reactions of epoxides with the higher order mixed organocuprates R2Cu(CN)Li2 (R = various alkyl or aryl) give excellent yields of ring-opened products. The trisubstituted oxiran (190), on reaction with Pr"Cu(CN)Li, affords only 23% of (191), but with Pr"2Cu(CN)Li2 the yield is increased to 86%. 

Primary amines. The reagent behaves as an electrophile toward higher-order organocuprates, transferring an NHSiMea moiety to one of the anionic ligands. 

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