Isoprene reactions with allylic

Reaction with isoprene epoxide. Alkyllithium reagents undergo 1,4-addition to isoprene epoxide to give predominately (Z)-allylic alcohols, particularly in the presence of a base (equation I). The reaction was used to prepare a-santalol (I) from n-bromotricyclene. 

Cycloaddition and ene reactions. Dienes >C=C—C=C< such as buta-1,3-diene, isoprene, 2,3-dimethylbuta-l,3-diene, fraws-piperylene, cyclopentadiene or anthracene react with 92 in Diels-Alder fashion to give [2 + 4] cycloadducts 410 (equation 128)62. Ene products 411 are formed additionally when the relative reaction rates for the [2 + 4] cycloaddition reaction and the ene reaction are comparable (e.g. for isoprene and 2,3-dimethyl-l,3-butadiene) Alkenes with allylic hydrogen (propene, 2-butene, isobutene) give ene products see equation 129. 

As an example of carbometallation, the 1,4-carbosilylation product 218 is obtained by the reaction of dienes, disilanes and acid chlorides of aromatic and a,/i-unsaturatcd acids at 80 °C. The phenylpalladium 216 is formed by the oxidative addition of benzoyl chloride, followed by facile decarbonylation at 80 °C, and reacts with butadiene to generate the benzyl-7i-allylic complex 217. Then, transmetallation with the disilane and reductive elimination afford 4-silyl-2-butenylbenzene 218 [92], Regioselective carbomagnesation of isoprene with allylic magnesium bromide 219 catalysed by Cp2TiCl2 gives 220, which is useful for terpene synthesis [93,94],... 

After reaction of the excess lithium with isoprene the enolate is alkylated with allyl bromide diastereoselectively from the less hindered face, opposite to the axial methyl group at the bridge head, to provide allyl ketone 3 as the single diastereomer. 

Cyclopentadienyl) (or related hgand). Treatment of (ry -allyl)dicarbonylnitrosyliron complexes (see Nitrosyl Complexes) with phosphite or phosphine gives five-coordinate ()] -allyl) complexes (22) of limited stability. The reaction of Fe(t-BuNC)5 with both aUyl bromide and chloride gives a product formulated as (23). Compounds of the general stracture (24) were prepared by reaction of [(CO)4Fe(SiR3)] and HFe(CO)4(SiR3) with allyl bromide and isoprene, respectively. ... 

Trost has reported enhanced enantioselectivity in the desymmetrization of mero-biscarbamates in the presence of triethylamine. Under these conditions, high yields (>80%) and enantiomeric excesses (93-99% ee) are obtained. This methodology has been applied to the synthesis of (—)-swainsonine. a-Amino esters have been used as nucleophiles in the reaction with acyclic allylic esters and isoprene monoepoxide, providing access to diastereoselective N-alkylated a-amino esters. By employing the feature ligand, asymmetric palladium(0)-catalyzed cychzation of 2-(tosylamino)phenol with ( -l,4-bis[(methoxycarbonyl)oxy]but-2-ene provides 2-vinylbenzomorpholine in 79% ee. A number of alternative diphosphine ligands were studied and found to be inferior. 

The rhodium-catalyzed addition of ethylene to 1,3-butadiene to yield 1,4-hexadiene (5a, 151) proceeds via a similar mechanism (151) with the exception that, upon formation of the alkylrhodium(III) species, the hexadiene synthesis proceeds without further change in the oxidation state of the metal. In these reactions with butadiene the coordinated alkyl groups are either chelate or 7r-allyl structures which appear to stabilize Rh(III) (151). The addition of propylene to butadiene and isoprene to produce [Pg.297]

We began our work with isoprene alcohol (see Scheme 11). While the Prilezhaev reaction with monoperoxyphthalic acid provided the appropriate dimethyl glycidol in good yield, we failed in our attempts to prepare the corresponding chiral epoxide by Sharpless epoxidation. Obviously, the reaction does not work in the case of this tertiary allylic alcohol. When the solution is allowed to warm up to room temperature a slow epoxidation takes place, however, the isolated dimethyl glycidol does not show any optical activity. Very recently the asymmetric epoxidation of a tertiary allylic alcohol in reasonable optical and chemical yield has been described [21]. 

The OH-isoprene reaction proceeds almost entirely by addition of the OH radical to the C=C double bonds. Formaldehyde, methacrolein (CH2=C(CH3)CHO), and methyl vinyl ketone (CH2=CHC(0)CH3) have been identified in the laboratory as major products of the OH-isoprene reaction. Figure 5.12a shows the initial steps of OH attack on isoprene. OH can add to four different positions in the isoprene molecule. The third and fourth radicals from the top of the figure are allylic radicals that have two radical centers, each of which yields a different peroxy radical when reacting with O2. The result is six different peroxy radicals, shown at the right of Figure 5.12a. Each of these peroxy radicals may react with NO, HO2, and RO2. We show, in Figure 5.12b, only the NO reaction pathways. The major products, methacrolein. 

The hydroboration of 1,3-dienes has also been reported, and these reactions generate Z-allylic boronic ester products. These reactions have been reported with palladium catalysts and are thought to occur through Tr-allyl intermediates. Reactions with butadiene and isoprene, followed by addition of the product to benzaldehyde, are shown in Equation 16.47. This equation also shows the presumed mechanism that proceeds by generation of a palladium allyl from the combination of diene and palladium hydride formed by oxidative addition of the borane. 

Halogenation of the isoprene enchainments in butyl elastomers yields halobutyl elastomers. Reaction of the isoprene units with elementary bromine or chlorine leads to the formation of allylic halide units along the chain—a substitution as opposed to addition across the double bonds. This leads to much faster curing, which permitted the development of tubeless tires, as adhesion of halobutyl to the rest of the tire could be achieved. Halobutyls are primarily used by the tire industry to form the inner liner of the tubeless tire. Other applications are similar to that of butyl. Chlorobutyl is also used in pharmaceutical stoppers. 

Method of synthesis cationic polymerization of high purity Isobutylene and isoprene is used to produce butyl rubber in the presence of complex systems of catalysts polymerization is terminated by irreversible destruction of the propagating carbenium ion by the collapse of the ion pair, by hydrogen abstraction from the comonomer, by formation of stable allylic carbenium ions, or by reaction with nucleophilic species such as alcohols or amines ... 

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