14-hydroxy bromination

Benz[e][ 1,2]azaborine, 1,2-dihydro-2-methyl-halogenation, 1, 656 Benz[6]- 1-azafulvenes dimerization, 4, 309 Benz[c]-2-azafulvenes dimerization, 4, 309 Benzazatropolone X-ray analysis, 7, 494 1 -Benzazepine, N-acetyl-6-hydroxy-bromination, 7, 528... 

Boekelheide rearrangement, 3, 303 Lumazine, 6,7,8-trimethyl-hydrogen exchange, 3, 303 Lumazine, 1,3,6-trimethyl-7-hydroxy-bromination, 3, 302 Lumazinecarboxylic acid occurence, 3, 324 Lumazine-6-carboxylic acid methylation, 3, 297... 

Incidentally, this represents a better route to 34 (11 %) than that shown in equation 26, since it is not complicated by concurrent formation of 35. The configuration of 34 was confirmed by catalytic hydrogenation, for this afforded a 4-bromo-cyclopentane-l,3-diol that was identical with one of the products of nms-hydroxy-bromination of 3-cyclopentenyl alcohol (Eq. 28). 

Substantial amounts of anti-Markovnikov products have been found for bromination of non-symmetrically substituted olefins RCH=CH2 in methanol, particularly with bulky R groups (R = Bib and Pr1)109. Mechanistic studies of a novel regiospecific hydroxy-bromination, employing CBr4, 02 and RO (R = Me, Pr1, Bu ) as reagents, suggest that both radical and carbanionic intermediates are involved180. 

Isocroionic acid, -crotonic acid, cis-croionic acid. Colourless needles m.p. 14 C, b.p. 169 C. Prepared by distilling -hydroxy-glutaric acid under reduced pressure. Converted to a-crotonic acid by heating at 180 C, or by the action of bromine and sunlight on an aqueous solution. 

When unsubstituted, C-5 reacts with electrophilic reagents. Thus phosphorus pentachloride chlorinates the ring (36, 235). A hydroxy group in the 2-position activates the ring towards this reaction. 4-Methylthiazole does not react with bromine in chloroform (201, 236), whereas under the same conditions the 2-hydroxy analog reacts (55. 237-239. 557). Activation of C-5 works also for sulfonation (201. 236), nitration (201. 236. 237), Friede 1-Crafts reactions (201, 236, 237, 240-242), and acylation (243). However, iodination fails (201. 236). and the Gatterman or Reimer-Tieman reactions yield only small amounts of 4-methyl-5-carboxy-A-4-thiazoline-2-one. Recent kinetic investigations show that 2-thiazolones are nitrated via a free base mechanism. A 2-oxo substituent increases the rate of nitration at the 5-position by a factor of 9 log... 

Reactions of the Aromatic Ring. The aromatic ring of hydroxybenzaldehydes participates in several typical aromatic electrophilic reactions. Ha.logena.tlon, Chlorination and bromination yield mono- and dihalo derivatives, depending on reaction conditions. Bromination of / -hydroxy-benzaldehyde in chloroform yields 65—75% of the product shown (39). 

Ha.loisoquinolines, The Sandmeyer reaction is commonly used to prepare chloroisoquinolines from the amino compound. The corresponding hydroxy compounds are also used by treatment with chlorides of phosphoms. The addition of bromine to a slurry of isoquinoline hydrochloride in nitrobenzene gives a 70—80% yield of 4-bromoisoquinoline [1532-97-4J. Heating 1-chloroisoquinoline [19493-44-8] with sodium iodide andhydriodic acid gives 1-iodoisoquinoline [19658-77-6] (179). 

Isothiazoles with electron-releasing substituents such as amino, hydroxy, or alkoxy in the 3- or 5-position are brominated in high yield in the 4-position. Alkylisothiazoles give lower yields, but 3-methylisothiazole-5-carboxylic acid has been brominated in 76% yield (72AHC(14)1). Again, thiazoles with an electron-releasing substituent in the 2- or 4-position are brominated at the 5-position (79HC(34-1)5). 

A very efficient one-pot procedure for the production of 3-hydroxy-3-cephems (45) has been developed which gives the desired product in almost 80% overall yield from (43a) which is readily available from penicillin. TTie sequence of reactions is (1) mesylation to give (43b), (2) formation of enamine (43c), (3) bromination to afford (44) and (4) hydroly-sis/cyclization with hydrochloric acid in methanol to afford (45) which, in some cases, crystallizes directly from the reaction mixture (B-82MI51000). 

Benzo[b]furan, 2,3-dihydro-2-phenyl-synthesis, 4, 697 Benzo[b]furan, 2,3-dihydroxy-tautomerism, 4, 37 Benzo[6]furan, 4,6-dimethoxy-acylation, 4, 606 Benzo[6]furan, 2,3-dimethyl-acetylation, 4, 606 bromination, 4, 605 photooxygenation, 4, 642 Benzo[b]furan, 5,6-dimethyl-2,3-diphenyl-applications, 4, 709 Benzo[b]furan, 1,3-diphenyl-vertical ionization potential, 4, 587 Benzo[b]furan, 2-ethoxy-5-hydroxy-synthesis, 4, 127... 

Chromone, 7-hydroxy-2-methyl-bromination, 3, 707 Chromone, 3-hydroxymethylene-synthesis, 3, 821... 

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