Acid bromides alkenic

Oxidative addition of aryl halides to [Pd(dba)2] in the presence of tetramethylethylenediamine or 2,2 -bipyridine to produce cis- [Pd(N-N)(Ph)X] proceeds easily when iodides are used but with more difficulty with bromides. Methyllithium reacts with the iodo complexes to give the mixed dialkyls. Cross coupling of alkenylboronic and arylboronic acids with alkenes is catalysed by palladium acetate in acetic acid. The reaction is believed to occur by oxidative addition of the carbon-boron bond across an in situ Pd(0) centre. 35... 

Addition of phenylmagnesium bromide to 4 tert butylcyclohexanone gives two isomeric ter tiary alcohols as products Both alcohols yield the same alkene when subjected to acid catalyzed dehydration Suggest reasonable structures for these two alcohols... 

As described in Section 2.3.2, vinylaziridines are versatile intermediates for the stereoselective synthesis of (E)-alkene dipeptide isosteres. One of the simplest methods for the synthesis of alkene isosteres such as 242 and 243 via aziridine derivatives of type 240 and 241 (Scheme 2.59) involves the use of chiral anti- and syn-amino alcohols 238 and 239, synthesizable in turn from various chiral amino aldehydes 237. However, when a chiral N-protected amino aldehyde derived from a natural ot-amino acid is treated with an organometallic reagent such as vinylmag-nesium bromide, a mixture of anti- and syn-amino alcohols 238 and 239 is always obtained. Highly stereoselective syntheses of either anti- or syn-amino alcohols 238 or 239, and hence 2,3-trans- or 2,3-as-3-alkyl-2-vinylaziridines 240 or 241, from readily available amino aldehydes 237 had thus hitherto been difficult. Ibuka and coworkers overcame this difficulty by developing an extremely useful epimerization of vinylaziridines. Palladium(0)-catalyzed reactions of 2,3-trons-2-vinylaziri-dines 240 afforded the thermodynamically more stable 2,3-cis isomers 241 predominantly over 240 (241 240 >94 6) through 7i-allylpalladium intermediates, in accordance with ab initio calculations [29]. This epimerization allowed a highly stereoselective synthesis of (E) -alkene dipeptide isosteres 243 with the desired L,L-... 

The bromination of benzene illustrates the difference between addition to alkenes and substitution of arenes. First, to achieve the bromination of benzene it is necessary to use a catalyst, such as iron(III) bromide. The catalyst acts as a Lewis acid, binding to the bromine molecule (a Lewis base) and ensuring that the outer bromine atom has a pronounced partial positive charge ... 

Diterpenoids related to lambertianic acid were prepared by intramolecular cyclization of either an alkene or an alkyne with a furan ring <2005RJ01145>. On heating amine 101 with allyl bromide, the intermediate ammonium ion 102 was formed which then underwent [4+2] cycloadditions in situ to give the spiroazonium bromides 103 and 104 (Scheme 13). These isomers arose from either endo- or co-transition states. The analogous reaction was also carried out with the same amine 101 and propargyl bromide. The products 105 and 106 contain an additional double bond and were isolated in 58% yield. The product ratios of 103 104 and 105 106 were not presented. 

The reaction of alcohols with CO was catalyzed by Pd compounds, iodides and/or bromides, and amides (or thioamides). Thus, MeOH was carbonylated in the presence of Pd acetate, NiCl2, tV-methylpyrrolidone, Mel, and Lil to give HOAc. AcOH is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a Pd compound, an ionic Br or I compound other than HBr or HI, a sulfone or sulfoxide, and, in some cases, a Ni compound and a phosphine oxide or a phosphinic acid.60 Palladium(II) salts catalyze the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective.61 A novel Pd11 complex (13) is a highly efficient catalyst for the carbonylation of organic alcohols and alkenes to carboxylic acids/esters.62... 

Ruasse et al, 1978) is totally regioselective and shows X-dependent chemoselectivity. This is partly in agreement with the kinetic data, which indicate no primary carbocation but rather a competition between the benzylic carbocation and the bromonium ion, depending on X. According to the data of Table 6, bridged intermediates would lead to more dibromide than open ions do. From these results and from those on gem-, cis- or frans-disubstituted alkenes, empirical rules have been inferred for chemoselectivity (i) more solvent-incorporated product is formed from open than from bridged ions (ii) methanol competes with bromide ions more efficiently than acetic acid. 

The conversion of the polystyrene-supported selenyl bromide 289 into the corresponding acid 290 allowed dicyclohexylcarbodiimide (DCC)-mediated coupling with an amidoxime to give the 1,2,4-oxadiazolyl-substituted selenium resin 291 (Scheme 48). Reaction with lithium diisopropylamide (LDA) and allylation gave the a-sub-stituted selenium resin 292, which was then used as an alkene substrate for 1,3-dipolar cycloaddition with nitrile oxides. Cleavage of heterocycles 293 from the resin was executed in an elegant manner via selenoxide syn-elimination from the resin <2005JC0726>. 

A few measurements are available that relate to the ion pair acidity of ethylene and some other alkenes. Ethylene is difficult to metallate directly, but vinyl bromides and iodides undergo facile transmetallation with alkyllithium reagents. Applequist and O Brien determined the equilibrium constants of transmetallation exchange reactions as a measure of relative acidity (equations 6 and 7)25. 

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