Ring opening bromide

The Kixnig reaction (Fig. 5) has been used to determine the amount of nicotinic acid and niacinamide. In this procedure, quatemization of the pyridine nucleus by cyanogen bromide is followed by ring opening to generate the putative dialdehyde intermediate. Reaction of this compound with an appropriate base, such as p-rr ethyl am in oph en o1 sulfate (47) or sulfanilic acid (48), generates a dye. The concentration of this dye is deterrnined c olo rime trie ally. 

Hydrogen bromide adds to acetylene to form vinyl bromide or ethyHdene bromide, depending on stoichiometry. The acid cleaves acycHc and cycHc ethers. It adds to the cyclopropane group by ring-opening. Additions to quinones afford bromohydroquinones. Hydrobromic acid and aldehydes can be used to introduce bromoalkyl groups into various molecules. For example, reaction with formaldehyde and an alcohol produces a bromomethyl ether. Bromomethylation of aromatic nuclei can be carried out with formaldehyde and hydrobromic acid (6). 

Benzo[a]quinoIizinium bromide, 7-methyl-electrochemical reductions, 2, 534 Benzo[c]quinolizinium bromide ring opening, 2, 533 Benzo[c]quinolizinium chloride hydrogenation, 2, 536 Benzo[c]quinoIizinium chloride, 6-amino-synthesis, 2, 554... 

Pyrido[2,l-6]benzothiazolium bromide, 4-ethoxy-5a,6,7,8,9,9a-hexahydro-l-methyl-9-oxo-X-ray diffraction, 6, 670 Pyridobenzoxazoles synthesis, 6, 190 Pyridocinnolines ring opening, 3, 240... 

If the addition of Br to the alkene results in a bromonium ion, the anti stereochemistry can be readily eiqilained. Nucleophilic ring opening by bromide ion would occur by backside attack at carbon, with rupture of one of the C—Br bonds, giving overall anti addition. 

There is no published mechanistic study on the Auwers flavone synthesis. The mechanism may involve the nucleophilic addition of oxonium 7, derived from 1, with hydroxide to give 8. Base-promoted ring opening of 8 could provide the putative intermediate 9, which then could undergo an intramolecular Michael addition to form 10. Expulsion of bromide ion from 10 would then give flavonol 2. 

The 3-oxidotriazolopyridinium zwitterions 245 fail to react with DMAD unless magnesium bromide is present, when ring opening occurs (2000H(53 265) (Section IV.F). The thiol 268 adds methyl acrylate as expected the resulting ester is converted via the acid hydrazide, to an oxadiazole (89IJC(B)170). 

Ring-opening products derived from primary amines are attractive precursors for the preparation of (3-lactams [57]. With methylmagnesium bromide as the base, diamino esters 33 cyclized readily in THF and stereospecifically generated anti-3-amino- 3-lactams 34 (Table 12.15). 

A synthetically useful diastereoselectivity (90% dc) was observed with the addition of methyl-magnesium bromide to a-epoxy aldehyde 25 in the presence of titanium(IV) chloride60. After treatment of the crude product with sodium hydride, the yy -epoxy alcohol 26 was obtained in 40% yield. The yyn-product corresponds to a chelation-controlled attack of 25 by the nucleophile. Isolation of compound 28, however, reveals that the addition reaction proceeds via a regioselective ring-opening of the epoxide, which affords the titanium-complexed chloro-hydrin 27. Chelation-controlled attack of 27 by the nucleophile leads to the -syn-diastereomer 28, which is converted to the epoxy alcohol 26 by treatment with sodium hydride. 

A procedure for a synthesis of dienyl sulfoxides (232 and 233) involves ring opening of dihydrothiophene 1,1-dioxide (231) by two molar equivalents of Grignard reagent (equation 141)136. The yields are usually in the 20-66% range. Similarly, treatment of the bicyclic sulfones 234, with 2 equivalents of phenylmagnesium bromide, produced a mixture of 1,4-dienylic sulfoxides (equation 142)136. 

Poly (dimethyl siloxane) obtained by anionic ring-opening polymerization of hexamethylcyclotrisiloxane (D3) can also be end-capped with vinylbenzyl bromide or other electrophiles, such as p. (chlorodimethylsilyl)styrene80). 

Nicotinic acid and related compounds react with l-chloro-2,4-dinitrobenzene in the manner of the cyanogen bromide reaction to yield derivative I, which possibly also decarboxylates at elevated temperature. In alkaline medium this derivative first adds an hydroxyl ion and then undergoes ring opening to yield the colored derivative II. 

Treatment of 19b with phenylmagnesium bromide gives diphenylacetylene (66) and the salt of benzenesulfmic acid Lithium aluminium hydride reacts with 19b similarly. These ring-opening reactions are similar to the reactions of organometallic reagents with the analogous thiirane dioxides (equation 17 above). 

Reactions of 69c with phenylmagnesium bromide afforded a complex mixture of ring-opened products. However, treatment of 69b with triethylamine afforded the 5,10-epoxydihydrodibenzoselenepine 70 in a 68% yield... 

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