Alkenyl mercurial

The reaction of alkenyl mercurials with alkenes forms 7r-allylpalladium intermediates by the rearrangement of Pd via the elimination of H—Pd—Cl and its reverse readdition. Further transformations such as trapping with nucleophiles or elimination form conjugated dienes[379]. The 7r-allylpalladium intermediate 418 formed from 3-butenoic acid reacts intramolecularly with carboxylic acid to yield the 7-vinyl-7-laCtone 4I9[380], The /i,7-titisaturated amide 421 is obtained by the reaction of 4-vinyl-2-azetidinone (420) with an organomercur-ial. Similarly homoallylic alcohols are obtained from vinylic oxetanes[381]. 

Organomercury reagents do not react with ketones or aldehydes but Lewis acids cause reaction with acyl chlorides.187 With alkenyl mercury compounds, the reaction probably proceeds by electrophilic attack on the double bond with the regiochemistry being directed by the stabilization of the (3-carbocation by the mercury.188... 

Alkenyl groups are transferred in preference to s-alkyl groups. The yields of trans-alkenylmercurials from RC=CH are greater than 85% yields from internal alkynes are lower. Use of (I) rather than tris(alkenyl)boranes leads to higher yields of alkenyl-mercurials. 

Alkynyl anions are more stable = 22) than the more saturated alkyl or alkenyl anions (p/Tj = 40-45). They may be obtained directly from terminal acetylenes by treatment with strong base, e.g. sodium amide (pA, of NH 35). Frequently magnesium acetylides are made in proton-metal exchange reactions with more reactive Grignard reagents. Copper and mercury acetylides are formed directly from the corresponding metal acetates and acetylenes under neutral conditions (G.E. Coates, 1977 R.P. Houghton, 1979). 

Mercuration. Mercury(II) salts react with alkyl-, alkenyl-, and arylboranes to yield organomercurials, which are usehil synthetic intermediates (263). For example, dialkyhnercury and alkyhnercury acetates can be prepared from primary trialkylboranes by treatment with mercury(II) chloride in the presence of sodium hydroxide or with mercury(II) acetate in tetrahydrofuran (3,264). Mercuration of 3 -alkylboranes is sluggish and requires prolonged heating. Alkenyl groups are transferred from boron to mercury with retention of configuration (243,265). 

Subshtuted 3-alken-l-ynes can be hydroaminated with primary or secondary aliphahc or aromatic amines at the alkynyl sites or at the alkynyl and at the alkenyl sites in the presence of Hg(ll) salts. However, the reachon is essentially stoichiometric in nature, even if the mercury compound can be recycled without apparent loss of achvity [262-264]. 

These reactions are compared with those of the equivalent 1-alkenyl HgCl compounds. Some differences are observed, notably that the mercury complexes will react with PhSe—SePh, while the tin complexes undergo no reaction at all. The reactions with ChHg, QHgCl and RHgCl, however, are broadly similar to that shown in reaction 26. 

Thiols react directly with non-activated alkynes [15] and with 1-alkynyl thioethers [16] to yield alkenyl thioethers in good yield (>76%), whereas thiocyanate anions only add to non-activated alkynes under acidic phase-transfer catalytic conditions on the addition of mercury(II) thiocyanate. Terminal alkynes are converted into vinyl thiocyanates, but disubstituted alkynes also form vinyl isothiocyanates [17]. Major by-products are the ketones formed by solvolysis of the alkynes. 

The reaction of heterocyclic lithium derivatives with organic halides to form a C-C bond has been discussed in Section 3.3.3.8.2. This cannot, however, be extended to aryl, alkenyl or heteroaryl halides in which the halogen is attached to an sp2 carbon. Such cross-coupling can be successfully achieved by nickel or palladium-catalyzed reaction of the unsaturated organohalide with a suitable heterocyclic metal derivative. The metal is usually zinc, magnesium, boron or tin occasionally lithium, mercury, copper, and silicon derivatives of thiophene have also found application in such reactions. In addition to this type, the Pd-catalyzed reaction of halogenated heterocycles with suitable alkenes and alkynes, usually referred to as the Heck reaction, is also discussed in this section. 

Several alkenyl hydroperoxides have been successfully cyclized to five-, six- and seven-membered ring peroxides (equation 241).38s 388 Alkaline sodium borohydride reduction of these mercurials is frequently accompanied by epoxide or cyclic ether formation. 

The photolysis of silacyclopropanes 21 and 22 by irradiation with a high-pressure mercury lamp proceeds simultaneously by two different routes, one leading to the formation of a 1-alkenyl substituted silane via a 1,2-hydrogen shift which has never been observed in the photolysis of the silacyclopropanes produced from methylphenylsilylene with olefins, and the other involving the usual 1,3-hydrogen shift. The photochemical reaction of 21 is shown in Eqs. (27) and (28) as a typical example. 

The photolysis of (Me3Si)3SiPh in the presence of functional substituted olefins is of considerable interest (55). Irradiation of 20 with a low-pressure mercury lamp in the presence of vinyl chloride or l-bromo-2-methyl-propene affords the respective 1-alkenyl-1-halo-1-phenyltrimethyldisilanes as the sole volatile product. The fact that the reaction of trimethylsilylphenylsilylene with butyl bromide does not give any volatile products suggests that compound 23 and 24 must come from a 1,2-halogen shift of... 

A mercury-free route to allyl vinyl ethers that relies on the Michael addition of allyl alcohols to unsubstituted alkenyl sulfoxides, followed by thermal loss of sulfenic acid and concurrent Claisen rearrangement has been described [145]. This methodology has been applied to the synthesis of isocar-bacyclin [146]. Posner reported an acid-catalyzed protocol that produces conjugated dienoate esters from allylic alcohols and a sulfinyl orthoester [147]. Additionally, the use of propargyl alcoholates and a chloro alkenyl sulfox-... 

Mercury photosensitization has been used to synthesize 1,3-dioxolane dimers by dehydrodimerization. For 1,3-dioxolane itself or analogues with substitution at C-2 or C-2 and C-4, radical formation occurs at the C-2 position, whereas when substitution is at the C-4 position radical formation occurs at the 4-position. In most cases, a small amount of product from ring opening was also reported <1996TL6853>. For 2,2-dimethyl-l,3-dioxolane, radical formation occurs at the 4-position, and one common way to achieve this is the use of dimethylzinc in air. Addition of various alkenes and related groups can then be performed, such as addition to tosyl imines <2004JOC1531>, and addition to perfluorinated alkenes and alkenyl ethers <1999JFC(94)141>. 

The reactions between dialkenyl- or diarylmercury derivatives and (ejco-5-acetoxy-tricyclo[2.2.1.0 ]hept-enmercury derivatives with an enrfo-5-alkenyl or an endo-S-aryX substituent, respectively. The best results were obtained in methanol much less satisfactory results were obtained in acetonitrile. Yields above 50% were obtained when diphenylmercury and bis(2-methylprop-l-enyl)mercury were employed giving 6 and 7, respectively. 

Intramolecnlar alkenylation at a furan a- or P-position by an alkyne occurs, with the formation of bicycUc derivatives, when promoted by mercury(II) acetate (or Hg(OAc)(OTf), generated in situ from mercuric acetate and scandinm triflate). In the case of closure onto a p-position, a spirocyclic intermediate from preferred attack at the a-position, may be involved, as shown. 

Mercury, Zinc, and Copper. The thermal decomposition of 2-thienylmercury thiocyanate, azide, acetate, and trifluoromethylsulphonate has been investigated. Thienylmercury derivatives have been cross-coupled with primary and secondary alkyl- and alkenyl-cuprate reagents. 2-Thienylzinc chloride has been coupled with iodobenzene and vinyl bromide, using Pd catalysis. ... 

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