Vinyl ketones bromination

Treatment of methyl vinyl ketone with sodium benzyloxide (1 esq.) followed by bromine (1 eq.) gave the expected alkoxy bromo ketone. Reaction of the latter with DBU in benzene at room temperature gave a 70% yield of 5-acetyl-3-benzyloxymethyl-2-methylfuran. 

Methylbenzophenone gives, on photochemical bromination (refluxing CCI4), 2-bromomethylbenzophenone in 80% yield. When the bromination was conducted at room temperature and the crude product treated in refluxing CHCI3 with iV-phenylmaleimide, dimethyl maleate, diethyl fu-marate, methyl vinyl ketone, dimethyl acetylenedicarboxylate, and 1,4-naphthoquinone adducts 92 (mp 227-228°C, 75%), 93 (mp 120-121°C, 65%), 94 (mp 129-130°C, 51%), 95 (mp 81-82 C, 23% an unidentified product was also isolated), 96 (mp 149-150°C, 62%) and 97 (mp 315-316°C, 19%) were obtained. l-Phenylbenzo[c]furan is assumed to be an intermediate in these reactions. Whereas the formation of 92-96 can be simply... 

A bimetal redox couple, zinc/cobaloxime, promotes hydropcrfluoroalkylation of electron-deficient alkenes, such as acrylates, acrylonitrile and methyl vinyl ketone, by perfluoroalkyl iodides and bromides, hydrogen replacing iodine or bromine. A typical reaction is the formation of2. ... 

Two new preparations of 1,8-cineole (553) [the biogenesis of which from geraniol (25) in Rosmarinus officinalis has been elucidated ] have been recorded. A Diels-Alder adduct 625 (R = Me) of methyl vinyl ketone and isopropenyl methyl ketone was converted to the diazoketone (R = CH = N2) with diethyl oxalate/base, then toluenesulfonyl azide, and treatment of the latter with [Rh(OAc)2]2 in methylene chloride at room temperature for five minutes converted it in very high yield to the tricyclic compound 626. Lithium dimethylcuprate then yielded the ketone 627, conversion of which to 1,8-cineole (553) was known.The other 1,8-cineole synthesis was a by-product of an observation which enabled the two stereoisomers of limonene 1,2-epoxide to be separated. The cjs-epoxide 549 was brominated to stereoisomers of a dibromocineole 628, under conditions when the rran.s-epoxide did not react, and could be distilled pure afterward. The dibromo compound 628 yielded 1,8-cineole (553) with tributyltin hydride. 

What product would you expect from the addition of bromine to methyl vinyl ketone Would you expect this addition to be more or less rapid than the addition of bromine to 1-butene Why ... 

In comparing the speed of the addition of bromine to 1-butene and methyl vinyl ketone, we realize that the double bond of 1-butene would be attacked more readily because it lacks the electron-withdrawing carbonyl group of methyl vinyl ketone. IThile methyl vinyl ketone is less reactive in electrophilic additions such as these, it is more reactive toward attack of nucleophiles. 

A ligand having C2-symmetry is not a necessity and a variety of catalysts are known that promote highly enantioselective Diels-Alder reactions. For example, the oxazaborolidine 148 is a good catalyst for the cycloaddition of cyclopentadi-ene and 2-bromoacrolein (3.104). The cycloaddition reaction is highly diastereo-and enantioselective in favour of the exo-aldehyde. However, the enantioselectiv-ity is poor with this catalyst when the dienophile lacks a substituent (for example bromine) in the 2-position. A solution to this problem is the use of the protonated oxazaborolidine 149, which promotes highly selective cycloaddition of cyclopen-tadiene with a range of dienophiles, such as ethyl vinyl ketone or ethyl acrylate (3.105). Asymmetric cycloaddition of a,p-unsaturated aldehydes or ketones with various dienes can alternatively be achieved in the presence of a chiral secondary amine as a catalyst. 

Dibromination of conjugated carbonyl compounds with diatomic Br2 generally gives a product where the C=C unit is converted to the dibromide. Reaction of 10 (methyl vinyl ketone) with bromine, for example, gives the expected addition product 42. Similar reactivity is expected with diatomic chlorine and iodine, although a-halo carbonyl compounds readily form ends that may react further, and they are prone to elimination. 

The starting material is a vinylamide, and it needs to be iodinated or brominated with retention of the amide Need to make a halogenated vinyl ketone bearing an electron-deficient arene... 

A good starting point for this chemistry would be a allylic alcohol. Conversion of this allylic alcohol into a chlorinated or brominated vinyl ketone can be accomphshed using oxalyl halides [179]. A gold-catalyzed process that affords the iodinated vinyl ketones was successful at room temperature [183]... 

Behavior similar to that of benzyl chloride is shown by benzyl chlorides and chloromethylated naphthalene substituted in the ring [57], certain N-benzoyllactams [16], and also possibly y-hexachlorane [59], DDT [60], and phenyl vinyl ketone at pH 10.7 [61]. An example of such a reaction investigated in detail is the elimination of a bromine ion from 2-acetyl-5-bromothiophene [17, 34], In the reduction of this compound in alkaline solutions the halfwave potential does not depend on the pH value and, with increase in the electrolyte concentration in the solution, is shifted to positive values this and other evidence is characteristic of the reduction of neutral and (in this case) unprotonated particles (a.g., [4, 10, 17]). 

The second cycloaddition substrate took to form of 91 (Scheme 1.9b), incorporating a vinyl sulfone dipolarophile. Beginning with cyano ketone 84, which was readily prepared from 1,5-dicyanopentane via a previously reported three-step sequence [45], condensation with thiophenol produced vinyl sulfide 85 in 84 % yield. Vinyl sulfide 85 underwent bromination in acetonitrile to afford bromo-vinyl sulfide 86 (86 %), which was then treated with isopropylmagnesium chloride [46] to effect metal-halogen exchange affording an intermediate vinyl magnesium bromide species. Subsequent alkylation with Mel in the presence of catalytic CuCN provided the alkylated vinyl sulfide 87 in 93 % yield. The nitrile within vinyl... 

Bromination of the enol ether product with two equivalents of bromine followed by dehydrobromination afforded the Z-bromoenol ether (Eq. 79) which could be converted to the zinc reagent and cross-coupled with aryl halides [242]. Dehydrobromination in the presence of thiophenol followed by bromination/dehydrobromination affords an enol thioether [243]. Oxidation to the sulfone, followed by exposure to triethylamine in ether, resulted in dehydrobromination to the unstable alkynyl sulfone which could be trapped with dienes in situ. Alternatively, dehydrobromination of the sulfide in the presence of allylic alcohols results in the formation of allyl vinyl ethers which undergo Claisen rearrangements [244]. Further oxidation followed by sulfoxide elimination results in highly unsaturated trifluoromethyl ketonic products (Eq. 80). 

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