Lithium bromide-Hexamethylphosphoric

DECARBOALKOYLATION Alumina. 1,4-DiazabicycIo[2.2.2]octane. Lithium bromide-Hexamethylphosphoric triamide. 

In agreement with this mechanism, it was found that the epoxide (4RS)-4,4-(epoxy-methano)tricyclo[5.1.0.02,5]octane-e c/o-8-carbaldehyde 2,2-dimethylpropaneT,3-diyl acetal (1) gave 4-oxotricyclo[6.1.0.02,6]nonane- ,/ttreatment with lithium iodide in tetrahydrofuran.71 Several examples employing this oxaspirohexane to cyclopentanone isomerization method are shown (see Table 7).69-80 Lithium bromide in the presence of hexamethylphosphoric triamide was also effective in these transformations.70,74,76 79,80... 

DEHYDROHALOGENATION Amidines, bicyclic. N-Bromosuccinimide. I, S-Dia-zabicyclo[4.3.0 nonene-5. Diethylamine. Dimethyl sulfoxide. Hexamethylphosphor-ic triamide. Lithium bromide. Potassium r-butoxkle. Sodium amidc-Sodium r-but-oxide. Tetia-n-butylammonium bromide. Triethylamine. 

Ring-opening reactions to yield aldehydes or ketones were reviewed [7-10]. Isomerization may be thermally induced [7] or may occur in the presence of basic or acidic agents [11]. Lithium bromide associated with tributylphosphine oxide or hexamethylphosphoric triamide (HMPA) has been used [12,13], but transition metal complexes may be more attractive [14-21]. In this work the performances of catalytic systems, e.g. "LiBr/HMPA/toluene", "Co2(CO) /MeOH", "NiBr2(PPh3)2/ Zn/PPh3/THF", etc. are compared for the isomerization of 3a and of analogues. Supported catalysts have also been studied. 

Displacements Boron trifluoride etherate. N,N-Diethyl-l,2,2-trichlorovinylamine. Dimethyl sulfoxide. Hexamethylphosphoric triamide. Lead acetate. Lithium bromide. Magnesium bromide. Polyphosphoric acid. Tetraethylammonium acetate. 

Bromination of an olefin and double dehydrobromination of the resulting 1,2-dibromide is a classical method for the generation of 1,3-dienes (Table 1). Bromination of a double bond can be done with molecular bromine or, more conveniently, with pyridinium bromide perbromide . A variety of bases has been employed for dehydrobromination. While potassium hydroxide and sodium methoxide have been used for a long time, lithium carbonate-lithium chloride in DMF or hexamethylphosphoric triamide (HMPA) works well in many cases . Double dehydrobromination with hindered bases such as potassium r-butoxide or diazabicyclononene (DBN) and diazabicycloundecene (DBU) give good results. 

The reported synthesis for (5Z,9Z)-14-methylpentadeca-5,9-dienoic acid (14) started with commercially available 4-methylpentan-l-ol, which upon reaction with phosphorous tribromide afforded l-bromo-4-methylpentane [52], Commercially available pent-4-yn-l-ol was also protected as the tetrahydropyranyl ether as shown in Fig. (18). Formation of the lithium acetylide with n-BuLi in THF and subsequent addition of 1-bromo-4-methylpentane in hexamethylphosphoric acid triamide resulted in the isolation of the tetrahydropyranyl protected 9-methyldec-4-yn-l-ol. Hydrogenation of the alkyne with Lindlar s catalyst and quinoline in dry hexane afforded the cis hydropyranyl-protected 9-methyldec-4-en-l-ol. Deprotection of the alcohol with />-toluenesulfonic acid afforded (Z)-9-methyldec-4-en-l-ol. Pyridinium chlorochromate oxidation of the alcohol resulted in the isolation of the labile (Z)-9-methyldec-4-enal. Final Wittig reaction with (4-carboxybutyl) triphenylphosphonium bromide in THF/DMSO resulted in the desired (5Z,9Z)-14-methylpentadeca-5,9-dienoic acid (14). 

In a similar way, 2,3-dimethoxybenzaldehyde with HO-protected 6-chlorohexan-1-ol and lithium afforded after acidic treatment 1,2-dimethoxy-3-(7-hydroxy-heptyl)benzene. Demethylation and bromide formation with boron tribromide gave 1,2-dihydroxy-3-(7-bromohepty0benzene which interacted with lithium-1-octyne in tetrahydrofuran containing hexamethylphosphoric triamide to give after selective catalytic hydrogenation, (15 1)-urushiol (ref. 138). In a different approach this has been synthesised in moderate yield from 2,3-dimethoxyphenyllithium and 1,7-dibromheptane as shown in the following scheme (ref. 139)... 

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