2.3- Dibromo-3-phenylpropanoate

Eliminations have also been carried out on a number of compounds of the form HalCH2CH2Y, where Y = OH, OR, OCOR, NH2, etc. these eliminations normally require conditions more drastic than for 1,2-dihalides, and metals or metal cations are found to be more effective than Ie. These eliminations are often found to be somewhat indiscriminate in their stereochemistry. The elimination of CO Br6 from the diastereoisomer (72) of 2,3-dibromo-3-phenylpropanoate in Me2CO is, however, found to proceed 100% ANTI, and under extremely mild conditions ... 

Dehalogenation of vicinal dibromides by electrogenerated polysulfide ions in DMA provides an indirect method to accomplish the same goal. A series of vicinal dibromides has been examined. These include methyl erj /2ro-2,3-dibromo-3-phenylpropanoate (152),... 

Cognate preparations. Phenylpropynoic acid. Place a solution of 88 g (84 ml, 0.5 mol) of ethyl cinnamate (Expt 6.137) in 50 ml of carbon tetrachloride in a 500-ml round-bottomed flask. Immerse the flask in ice and add 80 g (25.5 ml, 0.5 mol) of bromine from a separatory funnel slowly with frequent shaking. The halogen will disappear rapidly at first, but more slowly towards the end of the reaction no hydrogen bromide is evolved and the time of the addition is about 20-25 minutes. Allow the mixture to stand for 1 hour, pour the solution into a large evaporating dish and permit the excess of bromine and the carbon tetrachloride to evaporate spontaneously in the fume cupboard. The crude ethyl 2,3-dibromo-3-phenylpropanoate will remain as a solid cake this... 

ABSTRACT The gas-solid halogenation and hydrohalogenation using micro-crystalline cyclodextrin complexes are found to be efficient for production of the optical active halides of ethyl trans-cinnamate in moderate optical yields On exposure to HBr at 2QOC for 15-20 hr, the cinnamate in solid a- and S-cyclodextrin complexes yields ethyl R-(+)-3-bromo-3-phenylpropanoate in 46% e.e., and S-(-)-enantiomer in 31% e.e., respectively. No addition nor substitution products are obtained with HCl vapor at 0-50°C for 15-65 hr. Bromination of the B-cyclodextrin complex results in the formation of optical active ethyl erz/t/zrc>-2,3-dibromo-3-phenylpropanoate, while chlorination gives the optical active mixture of trans and cis addition products, ethyl erythro- and threo-2,3-di-chloro-3-phenylpropanoates in 60-80% yields. Mechanism of chiral induction in the present gas-solid reaction has been proposed on the basis of the crystal structure of the complex. 

The second stage (Experiment [D2]) involves the addition of bromine to the intermediate formed in the first step, frans-cinnamic acid. The product of this halogenation is e T/fizro-2,3-dibromo-3-phenylpropanoic acid. The stereochemistry involved in the formation of this second intermediate is a result of the nature of the anti addition of molecular bromine to a trans alkene. The details are given in the discussion in Experiment [D2]. 

Bromination of trans-Cinnamic Acid erythro-2,3-Dibromo-3-phenylpropanoic Acid... 

Common name eiyflzro-2,3-dibromo-3-phenylpropanoic acid CA number [31357-31-0]... 

Purpose. The bromination of frans-cinnamic acid is carried out to obtain en/flzro-2,3-dibromo-3-phenylpropanoic acid, the direct precursor to 2 -bromo-styrene, which is the synthetic target of Sequence D. You wiU review the stereospecificity of the addition of molecular bromine to an alkene. 

The bromination of alkenes is known to be a stereospedfic reaction. An example and detailed discussion of this addition to frans-stilbene is given in Experiment [A2b], and another example is illustrated in Experiment [F2], In the present case, bromine undergoes a similar addition, and the halogenated product obtained is the erythro diastereomer of 2,3-dibromo-3-phenylpropanoic add, which is produced as a racemic mixture of the two enantiomers. 

The en/flzro-2,3-dibromo-3-phenylpropanoic acid product prepared in this experiment has a melting point of 203-204 °C. The corresponding threo diastereomer has been synthesized and its racemate melts at 91-93 °C. Thus, the experimental results support the stereospecific nature of the bromine addition that is rationalized by the proposed mechanism. 

A 20- to 30-mg sample of the en/flzro-2,3-dibromo-3-phenylpropanoic acid may be recrystaUized (Craig tube) from chloroform (in the hood), if desired. 

Purpose. An elirnination reaction is carried out using en/fEro-2,3-dibromo-3-phenylpropanoic add, the direct precursor to 2 -bromostyrene. The influence of solvents and base on the course of the elimination reaction is illustrated. You will consider factors that control the stereospedfidty of a reaction. You will explore the option of using NMR spectroscopy to establish the ds/trans isomer ratio in the 2 -bromostyrene produd. 

Reagents and Equipment. Weigh and place 300 mg (0.97 mmol) of erythro-2,3-dibromo-3-phenylpropanoic acid (prepared in Experiment [D2]) and 300 mg (2.1 mmol) of potassium carbonate in a 25-mL Erlenmeyer flask. Add 5 mL of distilled water. 

Comment on the fact that eryf/zro-2,3-dibromo-3-phenylpropanoic acid undergoes elimination by an El pathway in water solvent (Fhrt A conditions), but by an E2 pathway (Thrt B conditions) when acetone is used as the solvent. 

Consider the stereochemistry of the carbocation intermediate formed under the conditions of Part A. Because the starting material used in this experiment, CTyf/zro-2,3-dibromo-3-phenylpropanoic acid, is racemic, the enantiomer of the carbocation shown must also be generated. Does the other enantiomer lead to the same diastereomer (ds) of the product or does it lead to the trans diastereomer ... 

Methyl eryr/zA o-2,3-dibromo-3-phenylpropanoate Methyl threo-2,3-dibromo-3-phenylpropanoate Methyl erythro- 2,3-dibromo-4-oxophenylbutanoate Methyl threo- 2,3-dibromo-4-oxophenylbutanoate Meso-1,2-dibromo-1,2-diphenyle thane c ,/-l,2-dibromo-l,2-diphenylethane... 

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