Trisubstituted and tetrasubstituted

Hydration of alkenes by this method however is limited to monosubstituted alkenes and disubstituted alkenes of the type RCH=CHR Disubstituted alkenes of the type R2C=CH2 along with trisubstituted and tetrasubstituted alkenes do not form alkyl hydrogen sulfates under these conditions but instead react m a more complicated way with concentrated sulfuric acid (to be discussed m Section 6 21)... 

The cis-trans naming system used in the previous section works only with disub-stituted alkenes—compounds that have two substituents other than hydrogen on the double bond. With trisubstituted and tetrasubstituted double bonds, a more general method is needed for describing double-bond geometry. (Tiisub-stitnted means three substituents other than hydrogen on the double bond tetrasubstituted means four substituents other than hydrogen.)... 

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... 

Trisubstituted and tetrasubstituted benzylidenecyclobutanes can be readily epoxidized and the resulting epoxides can be rearranged to 2-aryl cyclopentanones with either retention or inversion of configuration using Lil or Et AlCl, respectively (an example of trisubstituted benzylidenecyclobutane is shown in Scheme 11) [109, 110]. This method provides a convenient way to obtain optically active 2-aryl... 

Deoxygenation of epoxides. Hpoxidcs, particularly a,/)-disubstituted ones, are deoxygenated by reaction with P2I4 or PI3 in CS2 at room temperature in 70 90% yield. The reaction occurs with retention (>97%) of configuration. In the case of terminal, trisubstituted, and tetrasubstituted epoxides, the yields with P2I4 or PI3 are low ( 50%) unless pyridine or triethylamine is added. 

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. 

The cis and trans nomenclature for alkenes is an old method of classifying the configurational isomers of alkenes and is still in common use. However, it is only suitable for simple 1,2-di-substituted alkenes where we can compare the relative position of the two substituents with respect to each other. When it comes to trisubstituted and tetrasubstituted alkenes, a different nomenclature is needed. 

In summary, the range of highly electrophilic catalysts for the enantioselective hydrogenation of unfunctionalized trisubstituted and tetrasubstituted... 

The cycloisomerization of allenyl ketones can be exploited for the synthesis of 2,3,4- or 2,3,5-trisubstituted and tetrasubstituted furans, when the Pd(0)-catalyzed cyclization of a,7-disubstituted substrates is combined with the coupling of an aryl halide or substituted allyl halide, as has been reported by Ma et al. (Equation 14) <20000L941, 2000CC117, 2003CEJ2447>. 

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... 

Phosphonate carbanions are suitable starting materials for the synthesis of trisubstituted and tetrasubstituted olefins. In general, the olefins are formed with high ( )-selectivity. Another important advantage of the reaction is the fact that the by-product is a water-soluble phosphate which can easily be separated from the olefin. 

Over the past two decades, directed intermolecular Mizoroki-Heck reactions have been elaborated to remarkably high standards. Recently, Oestreich summarized the major advances in controlling both regio- and diastereoselectivity in these transformations [47]. With regards to the former aspect, the modular preparation of trisubstituted and tetrasubstituted alkenes is certainly a highlight within recent developments in Mizoroki-Heck chemistry [48],... 

Trisubstituted and tetrasubstituted benzylidenecyclobutanes 46 undergo highly enantioselective epoxidation with ketone 5b followed by epoxide rearrangement upon treatment with Et2AlCl or Li I to afford optically active 2-aryl cyclopentanones (48,49 or 50). ... 

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. 

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. 

Reactions of aryl aldehydes with p-substituted styrenes such as tran -P-methylstyrene and stil-bene also proceed well. The desired l,3-dihalo-2-substituted propanes are isolated in good yields (Scheme 23.20). However, reactions using a-methylstyrene or 1,1-diphenylstyrene do not afford the anticipated 1,3-dihalide products. Trisubstituted and tetrasubstituted styrenes are unreactive under the reaction conditions. 

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. 

However, the cis and trans notation does not describe isomeric trisubstituted and tetrasubstituted al-kenes because there is no longer a simple reference giving the relationship of groups to one another. For example, even the following relatively simple compounds cannot be designated as cis and trans isomers. 

In trans, trisubstituted, and tetrasubstituted olefins In vinyl, cis, and vinylidene olefins... 

Olefin cyclopropanation with diazoacetates proceeds in the presence of p-oxo-bis[(salen)iron(III)] complexes (Scheme 4-298, Scheme 4-299). The air-stable complexes are prepared from the corresponding salen ligands with iron(III) chloride hexahydrate in the presence of triethylamine. The method also allows the transformation of trisubstituted and tetrasubstituted olefins. No exclusion of air is required for this procedure. ... 

Most recently, Cramer and Jenkins have developed a novel tetracarbene iron(ll) complex 8, which was readily prepared by the reaction of the macrocyclic tetraimidazolium 7 with iron(ll) iodide using lithium diisopropylamide followed by the addition of thallium hexafluorophosphate (Scheme 2.12) [18]. Employing this catalyst system, aziridination reactions of various types of substituted aliphatic alkenes including trisubstituted and tetrasubstituted ones with both electron-donating and electron-withdrawing aryl azides were achieved. One advantage of this methodology is... 

Several recent papers deal with the restricted C—rotations in unsubstituted/" monosubstituted, NlsT-disubstituted, NN-disubsti-tuted, N,N,N -trisubstituted, " and tetrasubstituted " thioureas, together with the conformational aspects involved. The barriers to C—N rotation of thio- and seleno-urea were equal (AF = 12.8 kcal mol" ) and above that of urea (AF = 11,0 kcal mol" ). Restricted-rotation phenomena have been observed for substituted N-(tosylmethyl)thioureas, thiourea S-trioxides, " and 3-aryl-2-thiohydantoins. ... 

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