Bromides allyl

The method is essentially that of Merlmg and Jacobi. 140 g of allyl alcohol, CH2. CHCHaOH, are cooled in ice-water. A stream of hydrobromic acid, which may be conveniently generated by dropping bromine on naphthalene and passing the vapors through several bottles containing naphthalene, is then passed m until the liquid is saturated, after which it is boiled under a reflux condenser for one hour, the reaction being  

Under the conditions given very little addition of hydrobromic acid takes place at the double bond, although this would undoubtedly occur on long standing of the saturated solution m the cold. 

The mixture is then poured into water and the crude bromide separated and washed first with normal sodium 

94 g of phenol, 121 g. of allyl bromide, 140 g. of dry potassium carbonate, and 150 g of acetone are boiled for eight hours on the water bath under a reflux condenser In this case potassium carbonate is used to combine with the acid liberated in the alkylation, and the reaction is carried on in a non-aqueous solvent Potassium bromide soon separates and the mixture thickens, to a paste After cooling, water is added and then ether to take up the allyl phenyl ether. The ethereal layer is shaken out twice with 10 per cent sodium hydroxide solution to remove unchanged phenol, washed with a little water, and then dried over potassium carbonate and distilled m vacuo The yield should be 115-30 g., boiling at 85° under a pressure of 19 mm. The purification must be carried out under diminished pressure, as will be seen from the next experiment. 

Allyl phenyl ether is boiled under an air condenser until the temperature no longer rises, a process requiring four to six hours. From an initial temperature of about 190° the thermometer finally rises to about 2200. The gradual increase m boiling point is due to a re- 

In a 3-I. round-bottom flask, a hydrobromic add solution is made by the sulfur dioxide reduction of 480 g. of bromine in the presence of 510 g. of ice water or a mixture is made of 1000 g. of aqueous 48 per cent hydrobromic acid and 300 g. of concentrated su. furic acid. To this are added 385 cc. of aqueous allyl alcohol, which, according to bromine titration, contain 233 g. of pure allyl alcohol. The 3-I. round-bottom flask is fitted with a mechanical stirrer (Fig. 1, p. 4, see also Notes), separatory funnel, and an efficient condenser set for downward distillation. Stirring is started and 300 g. of concentrated sulfuric add are added gradually through the separatory funnel to the warm solution. The allyl bromide distils over completely in about one-half to one hour. The crude allyl bromide is washed with dilute sodium carbonate solution, is dried over calcium chloride and is distilled. The yield of product boiling at 60-72° from a number of experiments varies from 443 to 465 g. (92-96 per cent theory). A small high-boiling fraction is also obtained and examination has shown this to consist of propylene bromide. 

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A general method for the synthesis of l -alkenes is provided by the action of a Grignard reagent upon allyl bromide, for example ... 

If reaction does not occur when a little allyl bromide is first introduced, further addition must be discontinued until the reaction has commenced. Remove 2-3 ml. of the Grignard solution with a dropper pipette, add about 0-5 ml. of allyl bromide and warm gently to start the reaction after this has reacted well, add the solution to the main portion of the Grignard reagent. 

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. 

The allyl bromide (Section 111,35) should be dried over anhydrous calcium chloride and redistilled the fraction b.p. 69-72° is collected for use in this preparation. 

Allyl cyanide. Into a 1 5 litre three-necked flask (1), provided with a mercury-sealed stirrer and two long double surface condensers, place 293 g. (210 ml.) of freshly-distilled allyl bromide, b.p. 70-71° (Section III, 35) and 226 g. of dry cuprous cyanide (Section 11,50,3, Method 1), Remove the mercury-sealed stirrer and replace it by a tightly fitting... 

Review Problem 2 This allyl bromide is an important intermediate in the synthesis of terpenes (including many flavouring and perfumery compounds), as the five carbon fi agment occurs widely in nature. How would you make it ... 

Svndiesis (Crombie, J. Chem. Soc. (C), 1969, 1016). The acetylenic bromide corresponding to allyl bromide is called propargyl bromide and is reactive and readily available. We shall need to protect the ketone before we make the acetylene anion. It turns out tliat protection and decarboxylation can be done in one step. 

Only the more stable enolate (101 A) is formed and this reacts well with allyl bromide. This activating group (CHO) can be removed by basecatalysed hydrolysis. Mechanism ... 

Aside of benzene the chemist has a choice in which allyl she can use. Allyl alcohol, allyl bromide or allyl chloride can be used with equal success but allyl alcohol is a nice bonus because it is easier... 

Nickel-allyl complexes prepared from Ni(CO)4 and allyl bromides are useful for the ole-fination of alkyl bromides and iodides (E.J. Corey, 1967 B A.P. Kozikowski, 1976). The reaction has also been extended to the synthesis of macrocycles (E.J. Corey, 1967 C, 1972A). 

The allyl bromides formed by method (A) contain 25% of the undesired (Z)-isomer. The selectivity of the palladium-catalyzed amination can be steered by the application of polymer-bound systems (see section 2.6.3 B. M. Trost, 1978),... 

Synthesis of (A) started with the combination of 2,4,6-trimethylphenol and allyl bromide to give the or/Ao-allyl dienone. Acid-catalyzed rearrangement and oxidative bydroboration yielded the dienone with a propanol group in porlactone ring were irons in the product as expected (see p. 275). Treatment with aqueous potassium hydroxide gave the epoxy acid, which formed a crystalline salt with (R)-l-(or-naphthyl)ethylamine. This was recrystallized to constant rotation. 

It is known that tr-allylpalladium acetate is converted into allyl acetate by reductive elimination when it is treated with CO[242,243]. For this reason, the carbonylation of allylic acetates themselves is difficult. The allylic acetate 386 is carbonylated in the presence of NaBr (20-50 mol%) under severe conditions, probably via allylic bromides[244]. However, the carbonylation of 5-phenyl-2,4-pentadienyl acetate (387) was carried out in the presence of EtiN without using NaBr at 100 °C to yield methyl 6-phenyl-3,5-hexadienoate (388)[245J. The dicarbonylation of l,4-diacetoxy-2-butene to form the 3-hexenedioate also proceeds by using tetrabutylphosphonium chloride as a ligand in 49% yield[246]. 

Organoboranes are reactive compounds for cross-coupling[277]. The synthesis of humulene (83) by the intramolecular cross-coupling of allylic bromide with alkenylborane is an example[278]. The reaction of vinyiborane with vinyl-oxirane (425) affords the homoallylic alcohol 426 by 1,2-addition as main products and the allylic alcohol 427 by 1,4-addition as a minor product[279]. Two phenyl groups in sodium tetraphenylborate (428) are used for the coupling with allylic acetate[280] or allyl chloride[33,28l]. 

Indol-2-ylcopper reagents can also be prepared from 2-lithioindoles and they have some potential for the preparation of 2-substituted indoles. 1-Methyl-indol-2-ylcopper can be prepared by reaction of 2-lithio-l-methylindole with CuBr[10]. It reacts with aryl iodides to give 2-aryl-1-methylindoles. Mixed cyanocuprate reagents can be prepared using CuCN[ll], The cyan-ocuprate from 1-methylindole reacts with allyl bromide to give 2-allyl-l-methylindole. 

A 20% excess of ethylmagnesium bromide was prepared from magnesium (6.5 g) in ether (80 ml) by adding ethyl bromide (30 g) in ether (30 ml). Indole (25.8 g) in benzene (50 ml) was then added slowly with stirring and stirring was continued for 20 min after addition was complete. A solution of allyl bromide (29.2 g) in benzene (20 ml) was then added slowly. The mixture was stirred overnight and then diluted with ether and the product isolated and purified by distillation (22.7 g, 70% yield). 

Kharasch s earliest studies in this area were carried out in collab oration with graduate student Frank R Mayo Mayo performed over 400 experi ments in which allyl bromide (3 bromo 1 propene) was treated with hydrogen bromide under a variety of conditions and determined the distribution of the normal and abnormal products formed during the reaction What two prod ucts were formed Which is the product of addition in accordance with Markovmkovs rule Which one corresponds to addition opposite to the rule ... 

When however the ionic addition of hydrogen bromide to 1 3 butadiene is car ried out at room temperature the ratio of isomeric allylic bromides observed is differ ent from that which is formed at — 80°C At room temperature the 1 4 addition product predominates... 

Alkenes react with N bromosuccimmide (NBS) to give allylic bromides NBS serves as a source of Br2 and substitution occurs by a free radical mechanism The reaction is used for synthetic purposes only when the two resonance forms of the allylic radical are equivalent Otherwise a mixture of isomeric allylic bromides is produced... 

The starting material in the example is obtained by alkyl ation of ethyl acetoacetate with allyl bromide... 

Allyl phenyl ether is pre pared by the reaction of phenol with allyl bromide as described in Section 24 11... 

An asymmetric synthesis of estrone begins with an asymmetric Michael addition of lithium enolate (178) to the scalemic sulfoxide (179). Direct treatment of the cmde Michael adduct with y /i7-chloroperbenzoic acid to oxidize the sulfoxide to a sulfone, followed by reductive removal of the bromine affords (180, X = a and PH R = H) in over 90% yield. Similarly to the conversion of (175) to (176), base-catalyzed epimerization of (180) produces an 85% isolated yield of (181, X = /5H R = H). C8 and C14 of (181) have the same relative and absolute stereochemistry as that of the naturally occurring steroids. Methylation of (181) provides (182). A (CH2)2CuLi-induced reductive cleavage of sulfone (182) followed by stereoselective alkylation of the resultant enolate with an allyl bromide yields (183). Ozonolysis of (183) produces (184) (wherein the aldehydric oxygen is by isopropyUdene) in 68% yield. Compound (184) is the optically active form of Ziegler s intermediate (176), and is converted to (+)-estrone in 6.3% overall yield and >95% enantiomeric excess (200). 

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