Vinyl organometallics

As shown by Marvell and Whalley in 1970,5 divinylcyclohexa-nols, resulting from the reaction of a vinyl organometallic reagent... 

A second powerful route to functionalized allylboron compounds involves the reaction of an a-haloalkylboronatc and a vinyl organometallic reagent3 4-28-29, 50c-92 04. This method is especially useful for the preparation of allylboron compounds not accessible via the allylorganometal-lic route. Notable examples that fall into this category are ( )-4,4,5,5-tctramethyl-2-[4-(tetrahy-dro-2//-pyran-2-yloxy)-2-butenyl]-l,3,2-dioxaborolane (yield 41 %, 93% E) and (E)- or (Z)-2-(l,l-dimethyl-2-butenyl)-4,4,5,5-tetramethyl-1.3,2-dioxaborolane (yield 77-84%. 98% E or 93% Z). 

Addition of vinylic organometallic compounds to unsaturated carbonyl compounds addition of organometallic compounds to acetylenic carbonyl compounds... 

Cyanation of vinylic organometallic compounds Addition to activated alkynes (Michael)... 

Li and co-workers examined the addition of various aryl and vinyl organometallic reagents to a, 3-unsaturated carbonyl compounds in air and water. It was found that both Rh2(COD)2Cl2 and Rh(COD)2BF4 are... 

This sequence initiated by the nucleophilic cyclopropyl conjunctive reagent 9 allows facile annulation concommitant with regiocontrolled further structural elaboration as outlined in Eq. 8429). With the electrophilic conjunctive cyclopropyl reagent 58, this [3 + 2] annulation onto a vinyl organometallic (Eq. 85) has the availability of the... 

Leading examples of such performance are the transmetallation reactions of (Z)-vinylic tellnrides, easily generated by the hydrotelluration of alkynes, leading to (Z)-vinyl organometallic reagents, which are difficult to obtain by other currently available methods. 

A large number of vinyl organometallic monomers have been prepared, homopolymer-ized, and copolymerized with classic vinyl monomers by Pittman and others. These include polymers containing Mo, W, Fe, Cr (structure 11.33), Ir, Ru, Ti (structure 11.34), Rh (structure 11.35), and Co. 

Optimum reaction conditions for the preparation of l-d-aldehydes from aryl, benzyl, and vinyl organometallics are under investigation by the submitters. 

The cyclopropanation of vinyl organometallic and heteroatom substituted vinylic compounds has also been reported using zinc carbenoids. Vinylboronates (equation 37) °, -alanes (equation 38) °, -zincs (equation 39) °, -stannanes (equation 40) ° , -phos-phonates (equation 41) °, -germanes (equation 42) °, and silanes (equation 43) °° "° could be readily converted into cyclopropane derivatives. 

Isomerization of a-hydroxy alkynes and alkynones 2-15 Acylation of olefins 2-27 From lithium acetylides 2-32 From vinylic organometallic compounds... 

Unsaturated Nitriles, Nitro Compounds, and Sulfonic Acids and Esters 2-33 Cyanation of vinylic organometallic compounds... 

See also page 410, Section 2 for the halogenation of vinylic organometallics. 

Transition metal-catalyzed cross-coupling reactions between vinyl organometallic compounds and unactivated alkyl halides that can be usually performed with palladium, nickel and cobalt are of particular synthetic interest [37-39]. Recently, the groups of Cahiez [48] and Cossy [49] concurrently reported the first iron-catalyzed reaction of alkenyl Grignard compounds with primary and secondary alkyl halides (X=Br, I) (Scheme 5.15). The two protocols basically differ in the iron source... 

Addition Polymerization of Vinylferrocenes and Other Vinyl Organometallics... 

The coupling of vinyl organometallics to an alkyne unit has been extended to that involving the reaction of acetylenic bromides with trisubstituted vinylboranes this reaction is catalyzed by Cu(acac)2 and base, and is stereoselective with respect to the alkeny function (equation 45)50. 

The hydrometallation of alkynes is one of the most widely used routes to vinyl organometallics,131 which in turn are valuable in the construction of molecular structures containing carbon-carbon double bonds of defined stereochemistry. 

Usually, the reaction displays m-stereoselectivity giving (-E)-organomctallics. However, isomerization occurs very often leading to mixtures of (Z)- and (/. )-vinyl organometallics. The accepted general mechanism for the hydrometallation reaction involves the initial coordination of the alkyne to a vacant orbital of the metal, followed by insertion of the hydrogen-metal bond to a 7T-bond of the alkyne (Scheme 34).132... 

In view of the easy transformation of vinylic tellurides into reactive vinyl organometallics (see Section 9.13.8.2), the structures shown in Scheme 37 are valuable bifunctional synthons of conjugated olefins (Scheme 38). 

To have more insight into the reaction mechanism and the stereochemical outcome of the reaction, the following two experiments were performed. First, it was checked that the reaction of trisubstituted enol ether with two alkyl groups, such as 114, did not lead to the vinylic organometallic derivative [63] (Scheme 41), indicating that this tandem reaction should occur first by the isomerization of the remote double bond (only in the case of 98i, the direct transformation of methoxy-enol ether into an organometallic derivative was... 

This allylic C-H activation can be, in some specific cases, in competition with the direct transformation of monosubstituted enol ether into vinylic organometallic derivatives. Compound 116 reacts faster with 21 by the enol moiety to lead to 117 than with the remote double bond of 116, which would have given dienyl 118 after hydrolysis (Scheme 43). For the isomerization reaction to proceed, higher substitution of the enol ether is necessary. 

Perfluoroalkynylmetallics are more stable than pcrfluoroaliphatic or -vinyl organometallic reagents since the opportunity for a- or -elimination does not exist. The synthetic challenge, however, is to prepare perfluoroalkynylmetallics from readily accessible precursors. 

Scheme 17 Double diastereoselection with chiral vinyl organometallics...

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