Aluminums alkene elimination

Magnesium alkoxides (formed by ROH- -Me2Mg —>ROMgMe) have been decomposed thermally, by heating at 195-340°C to give the alkene, CEU, and MgO. Syn elimination is found and an Ei mechanism is likely. Similar decomposition of aluminum and zinc alkoxides has also been accomplished. ... 

A RAIR spectrum of the n-butyl surface species on Al(100) has been reported at 335 K in the fCH3/pCH2 region (203). A fCH3/pCH2 RAIR spectrum has been reported for the isobutyl group formed by the decomposition of triisobutylaluminum on Al(100) at 335 K (203), and a VEEL spectrum has been obtained from decomposition of the trialkyl-aluminum on Al(lll) at 100 K (204). These alkyl surface species are stable to 450-500 K and then decompose to give the expected alkenes by /3-H elimination. 

Methylenetriphenylphosphorane, 254 Titanium(IV) chloride-Lithium aluminum hydride, 310 (Z)-Alkenes By elimination reactions Dichlorobis(cyclopentadienyl)-titanium, 102 Hydrogen peroxide, 145 By hydrogenation of carbon-carbon triple bonds... 

Another common trapping method is an intramolecular aldol reaction of the initially formed anion, as shown in equation (91) and Schemes 53 and 54.% In the first case, an aldol-like trapping of the iminium salt produced (411 equation 91 ).96b The initial heteronucleophile in the other two cases is ultimately lost from the product by oxidation and elimination, so that the overall process is C—C bond formation at the a-center of an enone. Thus, treatment of the formyl enone (412 Scheme 53) with an aluminum thiolate afforded in 60% yield the trapped product (413) which could be oxidized and eliminated to give (414).96c Addition of the corresponding aluminate species to the ketoacrylate (415 Scheme 54) produced only one diastereomer of the aldol product (416) which was converted into the alkene (417) in excellent yield.96 1... 

Reductive elimination of (3-hydroxy sulfoximines with aluminum amalgam in acetic acid gives alkenes in good yields.70In one study, the resolved carbinol adducts of the ketone 93 and (+)-(S)-2b were individually treated with aluminum amalgam in acetic acid to give natural (-)-(3-panasinsene and its antipode in high enantiomeric purity.71... 

In the displacement reaction, reversible -hydride elimination of an alkene from an aluminum alkyl (equation 5) is followed by insertion of a different alkene into the Al-H bond of the resulting diaUcylaluminum hydride (equation 6). Three repetitions of this process yield the new trialkylaluminum compound as in equation (7). Tri-wo-butylaluminum obtained from the direct synthesis is a convenient starting aluminum alkyl for this process. 

Only single insertions into an Al-C bond occur for propene and higher alkenes and this is utilized for catalytic dimerization of propene as illustrated in Scheme 3. Insertion of propene into an Al-C bond of "PrsAl followed by )3-hydride elimination yields an aluminum hydride and 2-methylpent-l-ene. Insertion of propene into the Al-H bond regenerates "PrsAl. Thermal cracking of 2-methylpent-l-ene gives isoprene, which is subsequently polymerized with a Ziegler-Natta catalyst to form the synthetic rubber, cA-1,4-polyisoprene. 

Finch has demonstrated that the sulfoximine approach is a viable alternative for fluoromethylenation (Scheme 12). The fluorosulfoximine (54) is deprotonated with LDA in THF and the aldehyde or ketone added to the anion. Conversion to the alkene is carried out with the standard aluminum amalgam procedure to yield a 1 1 mixture of ( )- and (Z)-alkenes (56). The reaction is very effective for aromatic and aliphatic aldehydes and aliphatic and alicyclic ketones, but, while aromatic and a,p-unsaturated ketones give good yiel of the addition adduct, the reductive elimination results in a variable amount of product formation. This method was tilled to the synthesis of prostaglandin 9-fluoromethylene (58 equation IS).- ... 

Boeckman and coworkers studied the reaction of bis(thmethylsilyl) ester (361) with aldehydes to form the silyl-substituted unsaturated ester (362 equation 86). The anion was formed with potassium or lithium diisopropylamide. Other metals, such as magnesium or aluminum, were introduce by treating the lithium anion with Lewis acids. The addition step produced a single diastereomer, en ling the effects of counterion and steric bulk on the elimination to be ascertained. Excellent selectivity for the ( )-isomer (362) may be obtained by using K or Li cations and a sterically hindered aldehyde. In studies directed toward the synthesis of substituted pseudomonic acid esters, the Peterson alkenation was utilized to form a mixture of (Z)- and ( )-alkene isomers, one example of which (365) is depicted in equation (87). In this example the conditions were optimized to form the highest degree of selectivity for the (Z)-alkene. 

Aluminum halide catalysts are not effective isomerization catalysts for hydrogenated chlorofluorocarbons because of HCl elimination to form alkenes which are catalyst poisons. HF elimination from hydrofluorocarbons is not as facile, thus AIF3 [63] and AIClxF, 02 (x + y + 2z = 3) [64] are effective catalysts for the isomerization of 134 to 134a (eq 13). 

The acylation of alkanes has also been known for a long time, but for synthetic purposes is limited to simple substrates. The initial step is hydride abstraction by an acylium ion, a process well established in the presence of a powerful Lewis acid, most commonly an aluminum halide, or strong protic acid. The carbocation so formed can then undergo elimination, possibly after hydride or alkyl migration, to give an alkene which is then acylated. In the presence of excess alkane, saturated ketones are formed by a further intermolecular hydride transfer, whereas with an excess of acyl halide, the product is the (conjugated) unsaturated ketone. -" The synthetic potential is obviously likely to be limited to simple substrates. 

Dialkyl alanes may be added to a variety of substituted alkenes. Stable or unstable alkyl aluminum compounds are formed, depending upon the nature and location of the substituent in the alkene. An important part is also played by the direction of addition of the A]—H bond, which can be influenced by the substituents. Unstable alkyl alanes with functional groups mostly spontaneously go over as formed to alkenes and dialkyl aluminum compounds with the substituent directly bonded to the aluminum (e.g., R2AIX, R2A10R ) as a result of l,x elimination. 

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