Carbon Tetrabromide/Triphenylphosphine‐Activated Beckmann Rearrangement of Ketoximes for Synthesis of Amides

An efficient Beckmann rearrangement of ketoximes was developed using carbon tetrabromide/triphenylphosphine as an organocatalyst without addition of any acids or metals. The reaction showed good functional group tolerance and gave various amides in moderate to good yields.     

Stereoselective Ketone Rearrangements with Hypervalent Iodine Reagents

The first stereoselective version of an iodine(III)‐mediated rearrangement of arylketones in the presence of orthoesters is described. The reaction products, α‐arylated esters, are very useful intermediates in the synthesis of bioactive compounds such as ibuprofen. With chiral lactic acid‐based iodine(III) reagents product selectivities of up to 73 % ee have been achieved.     

Triflic acid–catalyzed rearrangement of unalkylated benzene sulfonanilides

Previous work has demonstrated that alkylated benzene sulfonanilides undergo sulfuric acid (98%)–catalyzed rearrangement to alkylamino diaryl sulfones. Similar treatment of their unalkylated analogs typically leads only to hydrolysis. Surprisingly, when the unalkylated benzene sulfonanilides react with triflic acid, rearrangement to sulfones does occur.     

Hexasulfanyl analogues of cyclotriveratrylene

The synthesis of four 3,4-di(alkylsulfanyl)benzyl alcohol derivatives is described, in five steps from methyl 3,4-di(hydroxy)benzoate via a Newman–Kwart rearrangement. Incubation of these derivatives in formic acid affords 2,3,7,8,12,13-hexakis(alkylsulfanyl)-10,15-dihydro-5H-tribenzo[a,d,g]cyclononene products, which are hexa-sulfanyl analogues of the well-known supramolecular cavitand host, cyclotriveratrylene (CTV). The yield of this cyclization depends strongly on the alkylsulfanyl substituents present, in the order SMe > SEt ≈ SiPr ? SBn. A crystal structure determination of one of the cyclotrimers shows a mode of self-association that is commonly exhibited by CTV itself.     

Hydrophobic Vitamin B12. X. Steric Effect in Electrochemical Carbon-Skeleton Rearrangement Catalyzed by Hydrophobic Vitamin B12 in Nonaqueous Media

Abstract

A steric effect in the carbon-skeleton rearrangement catalyzed by heptamethyl cobyrinate perchlorate, [Cob(II)7C₁ester]C10₄, was investigated under electrochemical conditions. The controlled-potential electrolyses of alkyl halides having two carboxylic ester groups of different bulkiness on the same carbon atom, such as 2,2-bis(ethoxycarbonyl)-l-bromopropane, l-bromo-2-tert-butoxycarbonyl-2-ethoxy-carbonylpropane, l-bromo-2-cyclohexyloxycarbonyl-2-ethoxycarbonylpropane, and l-bromo-2-ethoxy-carbonyl-2-phenoxycarbonylpropane, were carried out in N,N-dimethylformamide, as catalyzed by [Cob(II)7C₁ester]CIO₄, to give the corresponding ester-migrated products in the dark at—1.5 V vs SCE in the presence of acetic acid and at—2.0 V vs SCE without acetic acid. As regards a correlation between bulkiness of an ester group and a migration aptitude, a smaller ester group tends to migrate to the adjacent carbon atom more readily than a larger one. The origin of such a steric effect is discussed with attention to the rate-determining step.