Functionally Substituted Alkenes

The metathesis of unsaturated fatty-acid esters has received considerable attention. Aspects of the metathesis of fatty-acid esters and related compounds were recently reviewed by Boelhouwer.With the WCl6/Me4Sn system, both self-metathesis and co-metathesis (with symmetric alkenes) of unsaturated esters occur, provided that the double bond and the ester group are separated by at least one methylene group.As an example, conversion of C8-C=C-C7-COOC of 50% for self-metathesis and 70% for co-metathesis 

Nakamura, S. Fukuhara, S. Matsumoto, and K. Komatsu, Chem. Lett., 1976, 253. 

Nouguier, R. Mutin, J. P. Laval, G. Chaplet, J. Basset, and A. Lattes, Reel. Trav. 

Verkuijlen, R. J. Dirks, and C. Boelhouwer, Reel Trav. Chim. Pays-Bas, 1977, 96, 

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The ionic hydrogenation of carbon-carbon multiple bonds has been demonstrated only for the reduction of carbon-carbon double bonds which on protonation result in the formation of tertiary, or aryl-substituted, carbocations. The ability to use this reduction reaction with functionally substituted alkenes will be limited to those systems that do not contain functional groups that would otherwise react with trifluo-roacetic acid or the organosilane. 

Functional groups can substantially modify the regioselectivity (see Section 3.10.1.2, in particular equation 2 and Scheme 2). Some typical regioselectivities for functionally substituted alkenes are shown in Figure 3.. 4.9.2i-23 gre extensive accounts of the hydroboration of functional alkenes appear else-where. ... 

Table 14. Vinyl Lithiation of Functionally Substituted Alkenes... 

The alkenyllithium reagents are used for stereospecific syntheses of alkenes and functionally substituted alkenes. ... 

An important feature of the Suzuki reaction is that it allows cr/Z Z-alkenyl or alkyl-aryl coupling of fi-a//cy/-9-borabicyclo[3.3.3]nonane derivatives with haloalkenes and haloarenes without concomitant p-hydride elimination. The required organoboranes are obtained by hydroboration of the appropriate alkenes or functionally substituted alkenes with 9-BBN. The coupling reaction tolerates the presence of functional groups in both reaction partners, thus circumventing a requirement of their prior pro-tection. ... 

The reaction of enolates with dimethyl disulfides (MeSSMe) or diphenyl disulfides (PhSSPh) leads to the corresponding sulfides. Their oxidation to sulfoxides followed by heating provides a route to functionally substituted alkenes, such as a,[3-unsaturated carbonyl compounds. In the example below, the exocyclic alkene is formed since that is the only possible yn-elimination product. 

The regio- and stereoselective monohydroboration of 1 -alkynes or functionally substituted alkynes with dialkylboranes followed by protonolysis of the resultant alkenylboranes with a carboxylic acid is a powerful tool for the synthesis of 1-alkenes, and cA-disubsti-tuted and functionally substituted alkenes. ... 

In any chain reaction, apart from initiation steps, the termination steps are also important. In metathesis there are many possibilities for termination reactions. Besides the reverse of the initiation step, the reaction between two carbene species is also a possibility (eq. (17)). The observation that, when using the Me4SnAVCl6 system, as well as methane traces of ethylene are also observed [26] is in agreement with this reaction. Further reactions which lead to loss of catalytic activity are (1) the destruction of the metallacyclobutane intermediate resulting in the formation of cyclopropanes or alkenes, and (2) the reaction of the metallacycle or metal carbene with impurities in the system or with the functional group in the case of a functionally substituted alkene (e. g., Wittig-type reactions of the metal carbene with carbonyl groups). 

In 1968, Peterson made the important discovery that the anions resulting from lithiation of [(meth-ylthio)methyl]trimethylsilane and [(trimethylsilyl)methyl]diphenylphosphine sulfide reacted with benzophenone to produce lithiated P-hydroxysilanes, which decompose to give olefins by loss of McgSiOLi. " This olefination reaction resulting in functionally substituted alkenes has been extended to phosphonates and can be considered as an alternative to the Homer-Wadsworth-Emmons reaction. 

Barbot, F., Paraiso, E., and Miginac, P., A novel route to substituted phosphonates via conjugate addition of organometallics to l-(functionally) substituted alkene phosphonates. Tetrahedron Lett., 25, 4369, 1984. 

The hydroalumination of functionally substituted alkenes can be combined with... 

Dipolar Cycloaddition. The principal use of p-bromobenzenesulfonyl azide is in 1,3-dipolar cycloaddition reactions with functionally substituted alkenes. The reagent has been used at ambient temperature and pressure to convert simple trimethylsilyl and methyl enol ethers of cyclic ketones to ring-contracted p-bromobenzenesulfonimidates, and thence to the corresponding amides, esters, or acids (eqs 1 and 2). 

The presence of another unhindered carbon-carbon double or triple bond or functional group often affords a complex mixture of products resulting from competing hydroboration. As a result, the hydroboration of dienes, enynes, or functionally substituted alkenes produces a considerable amount of other products, which is highly undesirable for the subsequent utilization of the resulting organoborane. In addition, the stereoselective addition of borane is very poor in the absence of steric bulk, as shown ... 

The reactions of iron group metal carbonyls with functionally substituted alkenes have been reviewed. It was found that the reactions of the iron carbonyls with alkenes differ from those of the Ru and Os analogs. For Os, in particular, unsaturated ligands raise their hapticity to form unusual structures. ... 

Table 12.8. Relative Rates of Radical Addition as a Function of Alkene Substitution"...

The hydrostannation reaction can proceed either by a free-radical mechanism, or, with polar-substituted alkenes or alkynes, by a polar mechanism, respectively resulting in anti-Markownikoff or Markow-nikoff orientation. Both t3rpes of reaction are particularly suitable for preparing functionally substituted, organotin compounds. 

Hydrozirconation of terminal alkynes R-C=CH (R= aryl, alkyl) with 1 affords terminally ( )-Zr-substituted alkenes with high efficiency and excellent stereochemical and regiochemical control (>98%). These alkenylzirconocene complexes are of particular interest for synthetic use [136, 143, 144]. Moreover, beside the electropositive halogen sources [145] and heteroatom electrophiles [3] used in the pioneering studies to directly cleave the Zr-C bond, ( )-vinyl-Zr complexes were recently transformed into a number of other trans-functionalized alkenes such as ( )-vinyl-sul-fides[146], vinylic selenol esters [147], vinyl-sulfones [148], vinyl-iodonium [149], vinyl-(R0)2P(0) [150], and vinilic tellurides [143]. 

Some years ago we began a program to explore the scope of the palladium-catalyzed annulation of alkenes, dienes and alkynes by functionally-substituted aryl and vinylic halides or triflates as a convenient approach to a wide variety of heterocycles and carbocycles. We subsequently reported annulations involving 1,2-, 1,3- and 1,4-dienes unsaturated cyclopropanes and cyclobutanes cyclic and bicyclic alkenes and alkynes, much of which was reviewed in 1999 (Scheme l).1 In recent days our work has concentrated on the annulation of alkynes. Recent developments in this area will be reviewed and some novel palladium migration processes that have been discovered during the course of this work will be discussed. 

Polar-substituted alkenes where the functionality is not attached to a strained ring are considerably more discriminating in their compatibility with metathesis catalysts and as a rule require relatively high catalyst charges. In the aliphatic series, unsaturated esters have received the most attention. Boelhouwer reported in 1972 the metathesis of the ester methyl oleate and its trans isomer, methyl elaidate, with a homogeneous catalyst based on a 1/1.4 molar combination of WCl6/(CH3)4Sn (23). At 70°C and an ester/W molar ratio of 33, near-thermodynamic equilibrium was attained, and 49 and 52% of the respective esters were converted to equal amounts of 9-octadecene and the dimethyl ester of 9-octadecene-1,18-dioic acid. 

The reaction tolerated a variety of functionality, including ester and ether groups on the alkyl-substituted alkene at least two carbons away from the double bond, and raefa-nitro or para-methoxy substituents on the styrene. As expected, cross-metathesis occurred selectively at the less hindered monosubsti-tuted double bond of dienes also containing a disubstituted alkene (Eq. 8). 

The order of reactivity of these three catalysts towards alkenes (but also towards oxygen) is 1 > 3 > 2. As illustrated by the examples in Table 3.18, these catalysts tolerate a broad spectrum of functional groups. Highly substituted and donor- or acceptor-substituted olefins can also be suitable substrates for RCM. It is indeed surprising that acceptor-substituted alkenes can be metathesized. As discussed in Section 3.2.2.3 such electron-poor alkenes can also be cyclopropanated by nucleophilic carbene complexes [34,678] or even quench metathesis reactions [34]. This seems, however, not to be true for catalysts 1 or 2. 

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