4.5- disubstituted 3.4.5- trisubstituted

Degree of substitution. We classify double bonds as monosubstituted, disubstituted, trisubstituted, or tetrasubstituted according to the number of carbon atoms directly attached to the C=C stnactural unit. 

Parent Compound Monosubstituted Disubstituted Trisubstituted Tetrasubstituted... 

Carbon-carbon double bonds in unconjugated alkenes usually exhibit weak to moderate absorptions due to C=C stretehing in the range 1660-1640 em V Disubstituted, trisubstituted and tetrasubstituted alkenes usually absorb near 1670 cm The more polar carbon-carbon double bonds in enol ethers and enones usually absorb strongly between 1600 and 1700 crn k Alkenes conjugated with an aromatic ring absorb strongly near 1625 crn k... 

The catalyzed reaction of acetylenic esters and alkenes can lead to ene products and/or cis [2 + 2]cycloaddition. The relative reactivity of alkenes established by reactions with dienes is 1,1-disubstituted > trisubstituted > monosubstituted and 1,2-disubstituted. Ene reactions predominate with alkenes containing two substi tuents on one carbon.1... 

Palladium(II) salts, in the form of organic solvent soluble complexes such as PdCl2(RCN)2, Pd(OAc>2 or Li2PdCU, are by far the most extensively utilized transition metal complexes to activate simple (unactivated) alkenes towards nucleophilic attack (Scheme 1). Alkenes rapidly and reversibly complex to pal-ladium(II) species in solution, readily generating alkenepalladium(II) species (1) in situ. Terminal monoalkenes are most strongly complexed, followed by internal cis and trans (respectively) alkenes. Geminally disubstituted, trisubstituted and tetrasubstituted alkenes are only weakly bound, if at all, and intermolecular nucleophilic additions to these alkenes are rare. 

Snider demonstrated that AlCb catalyzed reactions of methyl propiolate with a wide variety of alkenes give good yields of 1 1 adducts. 1,1 -Disubstituted, trisubstituted and tetrasubstituted alkenes give exclusively ene adducts (30) (equation 2). 1,2-Diubstituted alkenes give exclusively cyclobutenes formed by stereospecific [2 + 2] cycloaddition (equation 3). Monosubstituted alkenes give mixtures of ene adducts and cyclobutenes. EtAlCh in CH2CI2 was found to be a more effective catalyst for this reaction since it can act as a proton scavenger as well as a Lewis acid. Optimal yields are usually obtained with... 

Complexes of the 4 type catalyze the hydroboration of various olefins with catecholborane at ambient temperature [173], The proposed mechanism of the hydroboration reaction - although not within the scope of this book - parallels that of the hydrogenation and hydrosilylation reactions. The architecture of both olefins (terminal > terminal disubstituted > internal disubstituted > trisubstituted) and organolanthanides (TOF(La) 10 TOF(Sm) TOF(5) = 4 TOF(4) affects the rate of hydroboration, which for 4(La CH(SiMc3)2) and 1-hexene is TOF = 200 h , for example. The observed high regioselectivities are exclusively anti-Markovnikov. For smaller metal centers (Y, Zr, Ti) and other ligand systems (bis(cyclopentadienyl), bis(benzamidinato)) inactivation of the catalyst by catecholborane or Lewis base-metal complex induced disproportionation of catecholborane appeared to compete effectively with the catalytic conversion [174]. 

Quite a considerable number of papers deal with the effect of structure of olefinic substrates on their reactivity in the catalytic hydrogenation 65). Lebedev 66) attempted a generalization of the problem. His conclusion that the rate of hydrogenation of olefins decreases in the order monosubstituted - symmetric disubstituted - asymmetric disubstituted - trisubstituted tet-rasubstituted ethylene derivatives is called the Lebedev rule. Campbell 67) supplemented it by demonstrating that the rate of hydrogenation decreases with the number and size of substituents on carbon atoms of the double bond, cis isomers are usually hydrogenated more quickly than trans isomers, and olefins containing the terminal double bond are more reactive than those with the double bond inside the chain. 

It has also been found that highly active catalysts can be prepared in situ by reducing a platinum, palladium, or rhodium salt with sodium borohydride in the presence of a carbon support. Similar reductions of nickel salts produce colloidal nickel-boron, which is highly selective toward olefins of different structural types. The normal order of reactivity—i.e., terminal > disubstituted > trisubstituted—is observed, but the reactivity spread is sufficiently large that selective hydrogenation of polyenes is possible, as illustrated by a step in a synthesis of the natural product... 

Zhang and Widenhoefer have reported a highly regio- anddiastereo-selective method for the intermolecular hydroalkoxylation of aUenes with alcohols [108]. As an example, reaction of 1-phenyl-l,2-butadiene with 2-phenyl-l-ethanol catalyzed by a 1.1 mixture of (IPr)AuCl [IPr = l,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] and AgOTf in toluene at room temperature led to isolation of ( )-(3-phenethoxy-l-butenyl)benzene in 96% yield as a single regio- and stereo-isomer (Eq. (12.38)). The protocol was effective for primary and secondary alcohols and for monosubstituted, 1,1- and 1,3-disubstituted, trisubstituted, and tetrasubstituted allenes. Transfer of moiety to the newly formed tetrahedral stereocenter in the y o oxy ation of axially chiral 1,3-disubstituted allenes ranged from 0 to 81%, epen ing on the nature of the allene and the concentration of the alcohol. 

Alkenoic acids given in Scheme 20 are also cyclized to give good yields of lactones.f t The relative reactivity of alkenes generally follows the order disubstituted > trisubstituted > monosubstituted, probably due to a fine balance between the electron density and steric bulkiness. exo-Methylene-y-butyrolactones can similarly be synthesized from the corresponding alkenyl carboxylic acids. ... 

Degree of substitution refers to the number of carbons directly attached to the C=C unit. An alkene of the type RCH=CH2 has a monosubstituted or terminal double bond regardless of the number of carbons in R. Disubstituted, trisubstituted, and tetrasubstituted double bonds have two, three, and four carbon atoms, respectively, directly attached to C=C. Among the C4Hg isomeric alkenes, only 1-butene has a monosubstituted double bond the other three have disubstituted double bonds and are, as measured by their heats of combustion, more stable than 1-butene. 

Asymmetric dihydroxylation reactions using the commercial materials (AD-mix-a, Aldrich 39,275-8 AD-mix-p, Aldrich 39,276-6) result in typical reaction times of 16-24 h for most alkenes at 0°C. For 1,2-disubstituted, trisubstituted, and tetrasubstituted alkenes further promotion by addition of methane-sulfonamide is also required. The dihydroxylation rate is considerably improved by increasing the osmium concentration in the commercial product from 0.2 mol% to 1 mol% by adding 3.68 mg of finely ground K2l0s(=0)2 0H)4) per 1.4 g of AD-mix-a (or AD-mix-p) and mixing well. 

Alkyl groups bonded to the sp -hybridized carbon atoms of alkenes affect the stability of the double bond. The chemical reactivity of alkenes also is often affected by the number of alkyl groups bonded to the sp -hybridized carbon atoms. Thus, it is useful to classify alkenes by the number of alkyl groups attached to the C=C structural unit. This feature is called the degree of substitution. An alkene that has a single alkyl group attached to the sp -hybridized carbon atom of the double bond is monosub-stituted. An alkene whose double bond is at the end of a chain of carbon atoms is also sometimes called a terminal alkene. Alkenes that have two, three, and four alkyl groups bonded to the carbon atoms of the double bond are disubstituted, trisubstituted, and tetrasubstituted, respectively. 

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