Acetyl hexachloroantimonate

Under nonequilibrium conditions the p,y-unsaturated ketone tends to predominate, which may be transformed to the more stable conjugated isomer. The intermediacy of 15 may allow further rearrangements to occur. However, acylation with preformed acylium ions, such as acetyl hexachloroantimonate, and in the presence of a base to prevent isomerization, affords exclusive formation of P,y-unsaturated ketones.109 This led to the suggestion of an ene reaction between the acylium ion and the alkene as a possible mechanistic pathway ... 

Acetyl hexachloroantimonate, CH3CO SbCle. Mol. wt. 374.51, colorless crystals sensitive to moisture. The salt is prepared from acetyl chloride and antimony(V) chloride. 

In contrast to the aromatic counterpart, very few works have been devoted to the mechanism of the aliphatic Friedel-Crafts acylation. Several mechanisms have been proposed to explain the reaction of 1-methylcyclohexene in acetic acid with zinc chloride catalyst that exclusively gives the 6-acetyl-l-methylcyclohexene. Early discussions by Deno suggest a carbo-cation intermediate. Finally, the observations by Beak of a product isotope effect in the absence of a corresponding kinetic isotope effect in the series of deuterated cyclenes is compelling evidence for a reaction intermediate, such as carbocation species. In the meantime, H.M.R. Hoffmann observed that the acylation of various olefins with acetyl hexachloroantimonate in methylene chloride in the presence of hindered amines affords 8,T-unsaturated ketones. He suggested that the non-conjugated enone is formed via an ene reaction. 

C2H3ClsOSb, Acetyl hexachloroantimonate, 32B, 318 C2H4ClS2Sb, 2-Chloro-1,3-dithia-2-stibacyclopentane, 32B, 319 C2Hi,ClgOi,Sb2, M Acetato-iLi-hydroxy-/i-oxo-bis trichloroantimony(V)), 45B, 774... 

Abbreviations Ac acetyl Bn benzyl BSP 1-benzenesulfinyl piperidine BTIB bis(trifluoroacetoxy)iodobenzene DAST (diethylamino)sulfur trifluoride DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTSF dimethyl(methylthio)sulfonium tetrafluoroborate DMTST dimethyl(methylthio)sulfonium triflate DTBMP 2,6-Ai-tert-butyl-4-methylpyridine DTBP 2,6-di-tert-butylpyridine DTBPl 2,6-di-tert-butylpyridinium iodide FDCPT l-fluoro-2,6-dichloropyridinium triflate FTMPT l-fluoro-2,4,6-trimethylpyridinium triflate IDCP iodonium dicollidine perchlorate IDCT idonium dicollidine triflate LPTS 2,6-lutidinium p-toluenesulfonate LTMP lithium tetramethylpiperidide Me methyl MPBT S-(4-methoxyphenyl) benzenethiosulflnate NBS A-bromosuccinimide NIS A-iodosuccinimide NlSac A-iodosaccharin PPTS pyridinium p-toluenesulfonate TBPA tris(4-bromophenyl)ammoniumyl hexachloroantimonate Tf trifluoromethanesulfonyl TMTSB methyl-bis(methylthio)sulfonium hexachloroantimonate TMU tetramethylurea Tr trityl TTBP 2,4,6-tri-tert-butylpyrimidine. 

The acetyl-iV ,iV -diisopropylcyanamidinium salt (201) undergoes reaction with arylaldehydes under mild conditions to yield 6-aryl-3,5-diisopropyl-5,6-dihydro-4-oxo-l,3,5-oxadiazin-3-ium hexachloroantimonates (202) as outlined in Scheme 30 <91T205>. 

Surprisingly, the equilibration studies consistently show a substantial proportion of the -D-arabino ion (75), as indicated by a corresponding proportion of tetra-0-acetyl-/3-D-arabinopyranose obtained after hydrolysis and subsequent analysis of the product mixture. The /3-D ion (75) cannot be formed through acetoxonium rearrangement of 72, but must arise through subsequent anomerization of the a-D ion (74) formed initially, because the acetoxonium salt functions as an effective catalyst for anomerization If solutions of anomerically pure aldopentopyranose tetraacetates in nitromethane are treated with 2-metiiyl-l,3-dioxolan-2-ylium hexachloroantimonate (2,R=Me), a rapid onset of anomeric equilibration is observed. Under these conditions, tetra-O-acetyl-D-arabinopyranose gives an a /3 ratio of 9 91, and tetra-O-acetyl-D-xylopyranose, an a /3 ratio of 96 4. 

Tetra-O-acetyl-a-D-idopyranosyl chloride (86) in carbon tetrachloride at 50 reacts with antimony pentachloride to give an acetox-onium salt that is a mixture of the hexachloroantimonates of the ions 87, 88, and 89. The composition of the salt, which, from its mode of... 

The initiator cation formed in this way can, in many cases then add directly on to the monomer to form the monomer cation. Examples of this are the polymerization of p-methoxystyrene or epoxides with trityl hexa-chloroantimonate, the polymerization of tetrahydrofuran with acetyl perchlorate, and the polymerization of vinyl ethers and A -vinyl carbazole with tropylium hexachloroantimonate, for example ... 

AcetyIonium hexachloroantimonate prepared by addition of acetyl chloride to a soln. of SbCls in chloroform and stirring at 0-5° for 45 min. dissolved in nitromethane, 3 g. 9a-fluoro-JLpregnene-ll, 17 a,21-triol-3,20-dione 21-acetate-benzene complex added, and allowed to stand 3 hrs. at 0-5° 2.5 g. 9a-fluoro-... 

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