Alkenyl compounds

The cis-trans isomerization of alkenyl ligands in transition metal alkenyl compounds is proposed to occur via zwitterionic carbene intermediates.46 According to this, the low contribution of the form b to the metal-dienyl bond in Os (Z)-CH=CHC(Me)=CH2 K1-0C(0)Me (C0)2(P,Pr3)2 could explain why this compound does not evolve into its (if )-isomer. 

The reactivity of OsHCl(CO)(P Pr3)2 toward alkynols depends on the substituents at the C(OH) carbon atom of the alkynol (Scheme 14).47 The reaction with 2-propyn-1 -ol initially affords the alkenyl compound 6s(CI I=CI ICII2OI I)Cl(CO) (P Pr3)2 in 85% yield, as a result of the anti-addition of the Os—H bond to the carbon-carbon triple bond of the alkynol. In chloroform-df solution this complex decomposes to a mixture of products, containing the derivatives OsCl2(CHCH=CH2) (CO)(P Pr3)2 and 6s(CHCHCH6)Cl(CO)(P Pr3)2 (Eq. 5). 

Isomerization of bis(tributylstannyl)alkenyl compounds catalyzed by RuCl(H)(CO)(PPh3)3 gave the corresponding allylbis(tributyl)tin compounds in good yields (Scheme 51). These compounds are useful intermediates in organic synthesis.89... 

Very interesting results were obtained from the reaction of magnesium alkylidene carbenoids with mefa-substituted arylamines (Table 8) . The reaction of magnesium alkylidene carbenoids 157 and 161 with three mefa-substituted anilines was carried out and the results are summarized in Table 8. The reaction of 157 with meta-anisidine gave two products 163 and 164 (in a 30 13 ratio) in 43% yield. The main product was found to have the alkenyl group at the more hindered position (163). As shown in the Table, all the other meto-substituted aniline derivatives also gave the more hindered alkenylated compounds as the main product in variable ratio. 

The coupling reaction with active halides such as allyl halides or acid chlorides catalyzed by cuprous halides afforded the corresponding alkenylated compounds [131,167,168] (Scheme 57). 

Surprisingly, there appear to be no examples of relevant nickel alkenyl compounds in the literature, nor is there any apparent reference to their unsuccessful pursuit. A single report describes the synthesis of an alkynyl complex, viz. the four-coordinate TplPr2Ni(C=CC02Me) (55),33 which was... 

Bis(tributylstannyl)alkenyl compounds, isomerization, 10, 94 /l-l,2-Bis(tributylstannyl)ethene, cross-coupling polymerization, 11, 659... 

Based on the evaluation of the results of physical measurements on polar alkenyl compounds described above, the position and configuration of the carbon-carbon double bond found in the apolar compounds is similar to that in the polar compounds, essentially for the same reasons. However, the combination of a low melting point and a high nematic clearing point of the bicyclohexane compounds (142,143 and 145) is remarkable. The birefringence and viscosity of these compounds is remarkably low. ... 

Alkenyl compounds, such as those shown in Tables 3.14—3.17 are used as major components of nematic mixtures for STN-LCDs with high information content, see Table 3 1,178,205,206 quoted in the table to give... 

Several of the trialkylaluminum and alkylaluminum halides and hydrides mentioned above are commercially available. Alkynyl, alkenyl, cyclopentadienyl, and aryl derivatives are, in general, not commercially available and must be synthesized for laboratory use. Alkynyl derivatives can be prepared by salt metathesis, as in the reaction of Et2AlCl with NaC=CEt to give Et2AlC=CEt. The acidity of terminal alkynes is sufficient for preparation of alkynyl aluminum compounds by alkane or hydrogen elimination upon reaction with a trialkylaluminum or an aluminum hydride (equation 17), respectively. TriaUcynyl aluminum compounds are typically isolated as Lewis base adducts to stabilize them against otherwise facile polymerization. Alkenyl compounds of aluminnm have similarly been prepared. 

The stability of the c-metal IB-carbon bond follows the order alkyl-M < aryl-M alkenyl-M < alkynyl-M [M = Cu(I), Ag(I), Au(I)L]. However, for Cu(I) and Ag(I), most alkyl, aryl and alkenyl compounds are only stable at < 0°C Furthermore, the stable organogold(I) species, with a few exceptions, have the general formula RAu(I)L, in which L is a neutral two-electron donor ligand. 

Organofunctional silanes with hydroxy-, epoxy-, acryl-, ester- and carboxy-functions are produced industrially. They are in particular utilized as additives for modification of polymers and for functionalizing silicones for different application sectors. Most of these compounds are manufactured by the addition of appropriately functionalized alkenyl-compounds. 

Styryl derivatives of 2-aminofurans, as well as alkenyl compounds, also undergo intramolecular cycloaddition and the alkene function can be introduced by Stille coupling of a suitably functionalised aryl iodide. This approach is illustrated by the tetrahydroquinoline synthesis summarised in Scheme 26 (99JOC3595). The iodo derivative 143 is readily prepared from the carbamate ester 142 (67% yield) and Stille coupling with vinyltributyltin gives the styrene 144 (72% yield). Intramolecular cycloaddition and dehydration is then achieved simply by heating compound 144 in toluene under reflux (24 h) to give the tetrahydroquinoline 145 in 79% yield. 

Indium metal reduces the terminal triple bond of aryl propargyl ethers, amines, and esters in aqueous ethanol to produce the corresponding alkenyl compounds (Tab. 8.23) [119]. Indium metal in aqueous ethanohc ammonium chloride reduces the carbon-carbon double bond of activated conjugated alkenes such as a,a-dicya-no olefins, /faryleriories, and enone esters (Scheme 8.88) [120]. 

The use of trifluoroborate salts in couplings, which are very easily prepared from boronic acids by reaction with KHF2, is a useful variant of the Suzuki reaction. These salts have the advantage of enhanced (often considerably) stabihty compared to boronic acids and this is particularly notable for alkenyl compounds, which can be stored for a considerable time. The coupling conditions are very similar to those for boronates and are apphcable to a wide range of heterocyclic substrates, ... 

H1 nuclear magnetic resonance measurements have established that, at least for the dialkyl alkynyl alanes, bridge bonds are formed exclusively by the a-carbon atom of the alkynyl group (30). This bond is stronger for the alkynyl than for the alkenyl compounds. In accordance with this, the dialkylalkynyl alanes may be distilled at reduced pressure as dimers without decomposition, whereas the corresponding alkenyl compounds decompose when heated and then undergo further reaction, in which addition of the A1—C bond to the C=C double bond occurs. The resulting aluminum alkyls disproportionate subsequently to trialkylalane and polymeric compounds (253). 

The alkenyl compounds which can be prepared from 1,5-hexadiene and dialkyl alanes are unstable and undergo intramolecular addition of the A1—C bond to the C=C double bond, which is sterically well sited (293) ... 

With hydride reagents such as dibal, Z-alkenes can be selectively obtained from alkynes in the phenolic lipid series (ref. 162), and related series of boron reagents greatly supplement the chemical methods of selective reduction and alkyiation. This selectivity has been achieved by the use of less reactive dialkylboranes such as bis(3-methyl-2-butyl)borane (di-isoamylborane), bis(2,3-dimethyl-2-butyl)borane (thexylborane), 9-boraUcyclo[3.kl]nonane (9-BBN) and dicyclohexylborane. Some applications in the polyethenoid field have been summarised (refs. 135,163) and the synthesis of alkenyl compounds generally reviewed (ref. 164). By the use of dibromoborane dimethylsulphide, an internal alkyne can be reduced selectively (ref. 165) as for example in the following way (R = n-alkyl). 

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