Dialkenyl cuprates

Z)-Alkenes. Lithium dialkyl cuprates undergo syn-addition to acetylene to afford (Z)-dialkenyl cuprates in quantitative yield. The products can be alkylated under conditions by which both alkenyl groups are used. In the case of reactive halides 2 equivalents of HMPT is necessary with less reactive halides 3 equivalents of trielhyl phosphite is also necessary (equation 1). The products are essentially only the (7,)-isomers.11... 

Dialkenyl cuprates react with a,/J-unsaturatcd sulfones to form (Z)-y,<5-unsaturated sulfones. Desulfonylation proceeds with retention of configuration.1-1... 

Dienes. 4 (Z)-Dialkenyl cuprates couple with alkenyl halides in the presence of Pd[P(C6H5)j]4 to form conjugated dienes in good yield, but with fair stereoselectivity. If 1 equivalent of zinc bromide (8, 86) is present, the configuration of the alkenyl halide is retained ( 99.5%). 

An alternative approach to conjugated dienes has been shown to proceed with high stereoselectivity. In this, dialkenyl cuprates can be coupled with vinyl iodides in presence of zinc bromide. 

A general route to (Z)-4-alkenoic acids (27) consists of condensation between dialkenyl cuprates (26) and jS-propiolactone. This extension of a general three-carbon homologation method is very efficient (83—90% yields), but does require the use of a considerable excess of the acetylenic precursor of (26). The isomeric ( )-4-alkenoic acids (29) can be obtained from vinylbutyrolactones (28) and alkyl copper reagents (cf. 4,179). The (E)-isomer of (28) unfortunately... 

Secondary and tertiary dialkylcuprates, lithium dialkenyl-, and even diphenyl-cuprates, add in very good yields to the reactive propionaldehyde diethyl acetal. The syn addition products may be trapped with a variety of electrophiles such as alkyl, alkenyl, alkynyl and aryl halides. The method has been used for the synthesis of several natural products. Substituted alkynic acetals also react with lithium dialkylcuprates in ether to furnish stable dialkenylcuprates of type (128) which do not eliminate to the corresponding alkoxy allenes (129) if the temperature is maintained below -20 C.164-179... 

Z)-Alkenylcuprates. (Z)-Dialkenyl tellurides, prepared from alkynes, are readily transformed into cuprate reagents by mixing with (2-thienyl)CuBu(CN)Li2. With these species all the typical cuprate reactions can be carried out. 

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