Carbocupration diene synthesis

In a similar manner, alkynes can undergo sequential carbometallation reactions, previously illustrated in equation (32).136 It is possible to combine carbocupration of alkynes with the use of a Michael acceptor as electrophile when that electrophile is a vinylphosphonium salt, carbocupration can be coupled to Wittig alkenation to result in a stereospecific synthesis of dienes via a one-pot, four-component, four carbon-carbon bond-forming reaction sequence.302... 

In this tandem allylic C-H bond activation, followed by an elimination reaction, substituted l-zircono-lZ,3 -dienes (zirconium moiety at the terminal position of the dienyl system) were easily prepared as unique isomers. With the idea of extending this methodology to the stereoselective synthesis of 3-zircono-1,3-diene (zirconium moiety at the internal position of the dienyl system), 119 was prepared and the reactivity was investigated with (1-butene)ZrCp2 21 (119 was obtained by carbocupration of the a-allyl alkoxy-allene, Scheme 35) [79]. When 119 was submitted to the tandem reaction, the diene 120 was isolated after hydrolysis as a unique ( ,Z) isomer in 75% isolated yield (Scheme 44). 

Alkenylcoppers have not been frequently used. However, generation of (Z)-/3-substi-tuted alkenylcoppers via carbocupration followed by their Pd-catalyzed cross-coupUng appears to be the method of choice in the synthesis of 1,4-disubstituted (Z,Z)-conjugated dienes. It also nicely complements the synthesis of 1,4-disubstituted ( , Z)-conjugated dienes by the hydrometallation-cross-coupling tandem process involving B, Al, and Zr. 

---