Allylic dibromides

The relationship of caracurine II to C-alkaloid D was established by converting the former, with hydrogen bromide, into the allylic dibromide (CII). Reduction of this product with zinc and acid then gave norbis-deoxy-C-alkaloid D. Information derived from one series can thus be applied in the other. 

The tellurolate-promoted anti-debromination by method G is extended to the preparation of conjugated dienes, starting from 1,2,3,4-tetrabromoalkanes and cycloalkanes, 1, 4-dibromo-2-alkenes and allylic dibromides. ... 

C-Dihydrotoxiferine (46, = 18,18 -bisdesoxy-toxiferine) can be prepared as follows on treatment with hydrogen bromide, caracurine V (44) undergoes ringopening to give the allylic dibromide (47), which with zinc and acetic acid can be debrominated to the naturally occurring bisnor-dihydrotoxiferine (48). Dimethylation gives C-dihydrotoxiferine (46). 

The cyclization of butadiene, as illustrated, involves the coupling of the 7r-allylnickel moiety. Various cyclic 1,5-dienes can also be synthesized by the coupling reaction of allyl dibromides using Ni(CO)4 via a 7r-allyl complex. 

Cyclization of allylic dibromides (1, 722-723 2, 290-292 3, 211 4, 355). Corey and Helquist have extended the synthesis of large-ring cycloalkenes by... 

Corey s synthesis of the sesquiterpene elemoH illustrates a novel method for construction of 1,2-divinylcyclohexanes involving the reaction of acyclic allylic dibromides and nickel carbonyl. 

The synthesis of j3-elemene outlined below6 is also based on the coupling of 1,10-dibromo-2,8-decadienes under influence of nickel carbonyl. The key allylic dibromide (B) has been built up from the unsaturated ester (A) utilizing a Claisen rearrangement and two successive phosphonate Wittig reactions. ... 

Allyl Bromide. Introduce into a 1-litre three-necked flask 250 g. (169 ml.) of 48 per cent, hydrobromic acid and then 75 g. (40-5 ml.) of concentrated sulphuric acid in portions, with shaking Anally add 58 g. (68 ml.) of pure allyl alcohol (Section 111,140). Fit the flask with a separatory funnel, a mechanical stirrer and an efficient condenser (preferably of the double surface type) set for downward distillation connect the flask to the condenser by a wide (6-8 mm.) bent tube. Place 75 g. (40 5 ml.) of concentrated sulphuric acid in the separatory funnel, set the stirrer in motion, and allow the acid to flow slowly into the warm solution. The allyl bromide will distil over (< 30 minutes). Wash the distillate with 5 per cent, sodium carbonate solution, followed by water, dry over anhydrous calcium chloride, and distil from a Claisen flask with a fractionating side arm or through a short column. The yield of allyl bromide, b.p. 69-72°, is 112 g. There is a small high-boiling fraction containing propylene dibromide. 

Quantitative Analysis of All llithium Initiator Solutions. Solutions of alkyUithium compounds frequentiy show turbidity associated with the formation of lithium alkoxides by oxidation reactions or lithium hydroxide by reaction with moisture. Although these species contribute to the total basicity of the solution as determined by simple acid titration, they do not react with allyhc and henzylic chlorides or ethylene dibromide rapidly in ether solvents. This difference is the basis for the double titration method of determining the amount of active carbon-bound lithium reagent in a given sample (55,56). Thus the amount of carbon-bound lithium is calculated from the difference between the total amount of base determined by acid titration and the amount of base remaining after the solution reacts with either benzyl chloride, allyl chloride, or ethylene dibromide. 

Benzyl- und Allyl-halogenide werden durch Lithiumalanat/Chrom(III)-, Vanadium(III)-, Titan(III)- und Wolfram(VI)-chlorid-Systeme zu substituicrten Athanen, geminate Dihalogenide zu substituierten Athylenen gekoppelt, vicinale Dibromide zu Alkenen debromiert8. 

Direct disconnection of (40) to dibromide (41) is a possibility, but it is better to make (40) from alkcne (42) as disconnection now gives an allylic bromide (43) available from cinnamic acid. 

In basic aqueous media, a kinetic study of the reaction between stannate(II) ions and alkyl halide shows that mono- and disubstituted organotin compounds are formed (Eq. 6.12a).27 The monosubstituted organotin compound is obtained after a nucleophilic substitution catalyzed by a complexation between the tin(II) and the halide atom. The disubstituted compound results from an electrophilic substitution coupled with a redox reaction on a complex between the monosubstituted organotin compound and the stannate(II) ion. Stannate(IV) ions prevent the synthesis of the disubstituted compound by complexation. Similarly, when allyl bromide and tin were stirred in D2O at 60° C, allyltin(II) bromide was formed first. This was followed by further reaction with another molecule of allyl bromide to give diallyltin(IV) dibromide (Eq. 6.12b).28... 

Mediated by Tin. In 1983, Nokami et al. observed an acceleration of the reaction rate during the allylation of carbonyl compounds with diallyltin dibromide in ether through the addition of water to the reaction mixture.74 In one case, by the use of a 1 1 mixture of ether/water as solvent, benzaldehyde was allylated in 75% yield in 1.5 h, while the same reaction gave only less than 50% yield in a variety of other organic solvents such as ether, benzene, or ethyl acetate, even after a reaction time of 10 h. The reaction was equally successful with a combination of allyl bromide, tin metal, and a catalytic amount of hydrobromic acid. In the latter case, the addition of metallic aluminum powder or foil to the reaction mixture dramatically improved the yield of the product. The use of allyl chloride for such a reaction,... 

The nature of the organotin intermediates has been studied. It was found that when allyl bromide and tin reacted in aqueous media, allyltin(II) bromide was first formed and then was followed by the formation of diallyltin(IV) dibromide (See also Section 6.4.1, Eq. 6.12b). Either of the two organotin intermediates can react with carbonyl compounds to give the corresponding homoallylic alcohols. However, the tin(II) species was found to be more reactive than the tin(IV) species (Eq. 8.38).81... 

Formation of the intermediate organomercury peroxide 56 was rationalised in terms of an allylic mercuration providing an unsaturated hydroperoxide 55 that can cyclise by the favoured 54) 5-exo mode (equation 42 X = 02CCF3). However, this was not the main reaction pathway and the yields (2.7% and 0.6% of 2,m-10-dibromo-8,9-dioxabicyclo[5.2.1]decanes 54 were an order of magnitude lower than those of the 2,6-dibromides 53 obtained from 1,4-cyclooctadiene. 

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

MeOH/AcOH-(Allyl)2SnBr2-(Pt) system at 50 55 °C. As illustrated in Scheme 149 [530], diallyltin dibromide (428) produced from metalKc Sn and allyl bromide in methanol reacts with carbonyl compounds (426) to give the allylated products (427) together with allyldibromotin monomethox-ide (430). The latter compound (430) may be reduced at the cathode to di- or zero-valent Sn, which reacts smoothly with allyl bromide to regenerate diallyltin di-bromide (428). 

Allylic and vinylic ethers via methoxytelluration of olefins (general procedure) To a solntion of phenyltellnrinm tribromide (2.22 g, 5 mmol), prepared from diphenyl diteUnride and bromine in methanol (5 mL), is added the olefin (10 mmol) and the mixture refluxed for 1 h. On cooling, the ()3-methoxy)alkyl or cycloalkylphenyltellnrinm dibromide precipitates and is separated by filtration. 

Method c. The dibromide is converted into the corresponding allylic methyl ethers by treatment with NaOH as described previously. 

The diazide (17) is obtained from the reaction of the dibromide (16) with sodium azide in The fluorodinitrobutyrate ester (18) is synthesized from the corresponding allyl... 

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