Addition alkene preparation with

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into trans-l,2-diols by acid-catalyzed hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with OSO4. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. In addition, alkenes react with divalent substances called carbenes, R2C , to give cyclopropanes. Nonhalo-genated cyclopropanes are best prepared by treatment of the alkene with CH2I2 and zinc-copper, a process called the Simmons-Smith reaction. 

Addition compounds called ozonides are produced when alkenes react with ozone and reductive cleavage of these compounds is used extensively in preparative and diagnostic organic chemistry. 

The Michael addition of nih oalkanes to alkenes substituted with two elecbon-withdrawing groups at the a- and 3-positions provides a new method for the preparation of functionalized alkenes. Although reactions are not new, Ballini and coworkers have used this sbategy in the synthesis of polyfunctionalized unsaturated carbonyl derivatives by Michael addition of nih oalkanes to enediones as shown in Eqs. 7.124-7.126. Success of this type of reaction depends on the base and solvent. They have found that DBU in acetonihile is the method of choice for this puipose. This base-solvent system has been used widely in Michael additions of nitroalkanes to elechon-deficient alkenes (see Section 4.3, which discusses the Michael addition). ... 

Olefin hydrocarbonylation can be used in conjunction with oxidative addition to prepare indanones and cyclopentenones, but the reaction is limited to terminal alkenes.243... 

Nitroalkanes react with Jt-deficient alkenes, for example, p-nitro ketones are produced from a,P-unsaturated ketones [41], whereas allylic nitro compounds have been prepared via the Michael-type addition of nitroalkanes with electron-deficient alkynes (Table 6.19). The reaction in either dimethylsulphoxide [42] or dimethyl-formamide [43] is catalysed by potassium fluoride in the presence of benzyltriethyl-ammonium chloride the reaction with dimethyl acetylenedicarboxylate is only successful in dimethylsulphoxide [42], Primary nitroalkanes produce double Michael adducts [42,44], A-Protected a-aminoacetonitriles react with alkynes under catalysed solidiliquid conditions to produce the Michael adducts [45] which, upon treatment with aqueous copper(Il) sulphate, are converted into a,p-unsaturated ketones. 

Oxymercuration-reduction of alkenes preparation of alcohols Addition of water to alkenes by oxymercuration-reduction produces alcohols via Markovnikov addition. This addition is similar to the acid-catalysed addition of water. Oxymercuration is regiospecific and auft -stereospecific. In the addition reaction, Hg(OAc) bonds to the less substituted carbon, and the OH to the more substituted carbon of the double bond. For example, propene reacts with mercuric acetate in the presence of an aqueous THF to give a hydroxy-mercurial compound, followed by reduction with sodium borohydride (NaBH4) to yield 2-propanol. 

Cyclopentadienes can be prepared by double Michael addition of zirconacyclopentadienes with propynoates <1997CC2069> or nucleophilic attack of zirconacyclopentadienes on acyl halides mediated by copper(l) chloride and accompanied by elimination <1995CC1503, 1996TL7521>. Tetraethylzirconacyclopentadiene with benzal chloride in THF in the presence of copper(l) chloride and DMPU yield l,2,3,4-tetraethyl-5-phenylcyclopenta-l,3-diene <2000TL7471>. A series of other similar compounds were prepared from tetra- -propylzirconacyclopenta-diene and 0 ,Q -dichlorotoluene, tetra- -butylzirconacyclopentadiene and 0 ,Q -dichlorotoluene or 0 ,Q -dibromotoluene, as well as some other combinations. Tetraethylzirconacyclopentadiene reacts with l,l-dibromo-l-alkene-3-ynes under the same conditions (copper(l) chloride and DMPU) to yield alkynylfulvenes. 

The acid or base elimination of a diastereoisomerically pure p-hydroxysilane, 1, (the Peterson olefination reaction4) provides one of the very best methods for the stereoselective formation of alkenes. Either the E- or Z-isomer may be prepared with excellent geometric selectivity from a single precursor (Scheme 1). The widespread use of the Peterson olefination reaction in synthesis has been limited, however, by the fact that there are few experimentally simple methods available for the formation of diastereoisomerically pure p-hydroxysilanes.56 One reliable route is the Cram controlled addition of nucleophiles to a-silyl ketones,6 but such an approach is complicated by difficulties in the preparation of (a-silylalkyl)lithium species or the corresponding Grignard reagents. These difficulties have been resolved by the development of a simple method for the preparation and reductive acylation of (a-chloroalkyl)silanes.7... 

Asymmetric Hydroboration. For reaction with a prochiral alkene, (/ ,/ )-2,5-dimethyl-B-methoxyborolane is liberated from (1) and a standard solution of the corresponding lithium dihydri-doborate in ether is prepared (eq 5). Hydroboration is effected by addition of lodomethane to the solution of dihydridoborate and alkene (eq 6). After oxidation, chiral secondary alcohols of high enantiomeric purity and predictable configuration are obtained from cis, trans, and (risubstituted alkenes. As is the case with other known asymmetric hydroborating agents, 2-methyl-1-alkenes react with low asymmetric induction. 

Examples of the application of this chemistry to the preparation of cyclobutanones, cyclobutenones, and P-lactams are presented in the Table. The mesityl thiol ester has proven to be particularly effective in reactions with less ketenophilic alkenes, although with the more reactive ketenophiles nearly identical results are obtained using either the mesityl a-diazo thiol ester or the more readily available thiophenyl ester. In the case of readily available ketenophiles, the reaction is best conducted using excess alkene, alkyne, or imine, but in other cases the cycloaddition can be carried out with excess diazo thiol ester. The efficiency of the reaction with unactivated alkenes is especially notable, and compares favorably with results obtained previously employing dichloroketene. For example, addition of dichloroketene to methylenecyclohexane is reported to proceed in 55% yield," while up to 81% of the desired [2-1-2] cycloadduct is produced in the reaction of (mesitylthio)ketene with this olefin under our conditions. 

Oxiranes are usually prepared from halohydrins. A general method of obtaining chloroalcohols from olefins is by the addition of hypochlorous acid formed in situ form -chloramides or fert-butyl hypochlorite. Bromoalcohols are produced from alkenes with Ai-bromosuccinimide or iV-bromoacetamide, while iodoalcohols are prepared with iodine in the presence of oxidants (iodic acid, oxygen, and nitrite). 

Thexylborane (ThxBH2, 1,1,2-trimethylpropylborane) is readily prepared by treating BHj THF or BH3 SMe2 in THF with 2,3-dimethy 1-2-butene in a 1 1 ratio. Although this monoalkylborane is crowded, it will hydroborate two additional alkenes provided they are not too hindered. 

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