Alkenylzinc reagent coupling

Regiocontrolled q- or / -alkenylation and arylation of cyclic enones are possible without protection of the ketone by applying the coupling reaction of the Q- or /3-halo enones 607 and 608 with aryl and alkenylzinc reagents[468,469]. 

A portion of the side chain of calyculin was prepared by a tandem reaction sequence that combined an alkenylzinc reagent with 2-bromoethenylboronate, followed by Suzuki coupling with a vinyl iodide in the same pot.230... 

The coupling of aryl- and alkenylzinc reagents with various halides has widespread use in the cross-coupling of aromatic rings [101]. The reactions of zinc derivatives of aromatic and heteroaromatic compounds with aryl and heterocyclic halides have wide synthetic applications [103,104],... 

Heterosubstituted 1,3-dienes. Some alkenylmetals substituted by OR, SR, or SiR, can be coupled with alkenyl halides (or aryl halides) in the presence of this Pd(0) catalyst. Alkenylzinc reagents, prepared by reaction of alkenyllithiums with ZnCh, and alkenyl-alanes are the most useful. Yields from reactions with organoboronates are low. 

Alkenylzinc reagents. Hydrozirconation of l-alkynes followed by treatment with MeLi, MejZnLi provides alkenylzincates, which are useful for transfer of alkenyl groups to enones. Prostaglandins and substances of similar skeleton are accessible by a 3-component coupling. 

An alternative preparation of stereodeflned cw-a,/3-substituted alkenylzinc reagents involves transmetallation of the corresponding trialkenylboranes or alkenyl tellurides with diethylzincJ f The alkenylzincs thus obtained undergo Negishi coupling with aryl iodides in good yields (Scheme 31). 

Scheme 4.52 a-Selective Pd-catalyzed cross-coupling of alkenylzinc reagents with allylic halides [190]. 

Scheme 3.7 Cross-couplings of a-bromo nitriles with aryl- and alkenylzinc reagents.

C generates in situ the corresponding alkenylzinc reagent 9. Its Pd-catalyzed cross-coupling reaction provides an alternate and complementary route to conjugated enynes and oligoenynes. Thus, for example, a difunctional trienyne 10 suitable for the synthesis of 6,7-dehydrostipiamide (11) has been synthesized from... 

The range of nucleophiles can be extended to alkenylzinc reagents. These species are subjected to alkyl chlorides, bromides, or iodides in an iron-catalyzed Negishi coupling to efficiently form olefins (Scheme 4-235). Iron(III) chloride fiinctions as a precatalyst in the presence of TMEDA. ... 

Scheme 4-235. Negishi coupling of alkyl halides with alkenylzinc reagents catalyzed by FeCb/TMEDA.

Organozinc compounds are also useful in palladium-catalyzed coupling with aryl and alkenyl halides. Procedures for arylzinc,156 alkenylzinc,157 and alkylzinc158 reagents have been developed. The ferrocenyldiphosphine dppf has been found to be an especially good Pd ligand for these reactions.159... 

E)-(2-Bromoethenyl)dibromoborane, BrCH==CHBBr2, can be used in place of 1 to couple alkylzinc chlorides with an alkyl chloride to form a monoene, but this reagent is unsatisfactory for coupling of alkenylzinc chlorides.1... 

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