Olefin three-carbon, additions

The procedure described here serves to illustrate a general [3+2] annulation method for the synthesis of cyclopentane derivatives. A unique feature of this one-step annulation is its capacity to generate regio-specifically five-raembered rings substituted at each position, functionally equipped for further synthetic elaboration. As formulated in the following equation, the reaction proceeds with remarkably high stereoselectivity via the effective suprafacial addition of the three-carbon allene component to an electron-deficient olefin ("allenophile"). ... 

Additions to functionalized three-carbon olefins have been studied extensively. We have used methyl acrylate as a standard olefin since it always reacts only at the terminal carbon and the a,/3-double bond in the product is always trans. The stereospecificity of its reactions with vinylic halides varies with structure. The simple 1-halo-l-alkenes with methyl acrylate under normal conditions give mixtures of E,Z- and E,E-dienoates. The reaction is more selective with the bromides than with the iodides and the stereoselectivity increases with increasing triphenylphosphine concentration. This occurs because the excess phosphine displaces the hydridopalladium halide group from the diene 7r-complex before readdition to form the ir-allylic species occurs (see Equation 6). The disubstituted vinylic bromides react stereospecifically with methyl acrylate (4). 

Conversion of olefins into esters. Brown1 has extended the one-carbon homologation of olefins with carbon monoxide and the three-carbon homologation of olefins with acrolein to a two-carbon homologation with ethyl bromoacetate. The olefin is converted into the trialkylborane in THF at 0° by addition of the calculated quantity of diborane in THF. An equimolecular quantity of ethyl bromoacetate is added, followed by an equimolecular quantity of potassium f-butoxide in t-butanol. The reaction is apparently complete immediately. Ethyl chloroacetate can also be used, but the reaction is somewhat slower and gives slightly lower yields. 

Acrolein is the prototype a,[3-unsaturated aldehyde, and reacts across N2 and N1 of dG to add three carbons and generate the exocyclic tetrahydropyrimidopurinone ring (propano ring) (Figure 5.4). The reaction occurs via Michael addition of the olefin to either N1 or N2 followed by 1,2-addition of the aldehyde to N2 or Nl, respectively. l,N2-8-Hydroxy-propanodeoxyguanosine (y-OH-PdG) and l,N2-6-OH-PdG (a-OH-PdG) are the principal products with the former being the major isomer [60, 61]. 

Related to this process in terms of the structure of the three-carbon component is the use of x.of-dibromo ketones in combination with diiron nonacarbonyl [Fe2(CO)9]4 The addition of the resultant oxyallyl iron(II) cation to a range of olefins allows the isolation in moderate to good yield of the substituted cyclopentane 3. 

A number of mechanistically related procedures involving the use of allylmetal reagents as the three-carbon unit in stereoselective [3 + 2] cycloadditions have been documented. In general, the additions to electron-deficient olefins occur in the presence of Lewis acids and appear to proceed via a carbocationic intermediate which on 1,2-migration of the carbon-metal bond and subsequent cyclization provides the corresponding functionalized cyclopentane ring. 

The stereochemically controlled addition of organometallic species of copper, tin, silicon, palladium, zirconium, and boron to acetylenes has been investigated as a route to di-, tri-, and tetra-substituted olefins. The carbon-metal bond thus formed is cleaved in a stereoselective manner either directly, or indirectly, via the corresponding vinyl-lithium reagents with a wide variety of electrophiles. In three... 

Shell Higher Olefins Process (SHOP). In the Shell ethylene oligomerization process (7), a nickel ligand catalyst is dissolved in a solvent such as 1,4-butanediol (Eig. 4). Ethylene is oligomerized on the catalyst to form a-olefins. Because a-olefins have low solubiUty in the solvent, they form a second Hquid phase. Once formed, olefins can have Htfle further reaction because most of them are no longer in contact with the catalyst. Three continuously stirred reactors operate at ca 120°C and ca 14 MPa (140 atm). Reactor conditions and catalyst addition rates allow Shell to vary the carbon distribution. 

Unsaturated Hydrocarbons. Olefins from ethylene through octene have been converted into esters via acid-catalyzed nucleophilic addition. With ethylene and propjiene, only a single ester is produced using acetic acid, ethyl acetate and isopropyl acetate, respectively. With the butylenes, two products are possible j -butyl esters result from 1- and 2-butylenes, whereas tert-huty esters are obtained from isobutjiene. The C5 olefins give rise to three j iC-amyl esters and one /-amyl ester. As the carbon chain is lengthened, the reactivity of the olefin with organic acids increases. 

Radical-based carbonylation procedures can be advantageously mediated by (TMSlsSiH. Examples of three-component coupling reactions are given in Reactions (74) and (75). The cascade proceeds by the addition of an alkyl or vinyl radical onto carbon monoxide with formation of an acyl radical intermediate, which can further react with electron-deficient olefins to lead to the polyfunctionalized compounds. ... 

In many of the above examples the number of electrons happens to be the same as the number of atoms in each component. But this is not always the case. For example in 1, 3 dipolar cycloaddition, the 1, 3 dipole has four electrons distributed on three atoms. The addition of a 1, 3 dipole to an olefine will give 3+2 carbon atoms in the ring but it will have 4k +2k electrons according to the adopted system... 

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