Carboxylic acid fluorides rearrangement

Synthesis of trifluoromethylated compounds 152 has been achieved via ester-enolate [2,3]-Wittig and [3,3]-lreland-Claisen rearrangements. Perfluorocyclo-butane phosphonium ylides, e.g. 153, have been used as a masked fluoride anion source in their reactions with alcohols and carboxylic acids which lead to alkyl-and acyl-fluorides. Ylides 153 are also reported to cleave Si-C and Si-O bonds, cause dimerisation of fluoro-olefins, and also react with acid chlorides or other activated aromatic compounds under halogen exchange. ... 

Electrophilic addition of hydrohalic acids (hydrogen fluoride, hydrogen bromide, hydrogen chloride), carboxylic acids (e.g. acetic acid) and halogens (bromine, chlorine, iodine) to bicy-cloheptadiene gave a homoallyl cation which underwent rearrangement to nortricyclyl derivatives, i.e. 5-substituted tricyclo[2.2.1.0 ]heptanes. ... 

Simple alcohols and aldehydes are efficiently oxidized to carboxylic acids using solid NaMn04-H20 yields around 70% are obtained. Rearrangement products are sometimes observed in the conversion of a-amino acids to a-fluoroacids using NaNOa in polyhydrogen fluoride-pyridine/ However, this problem is effectively suppressed by the use of 48 52 (w/w) hydrogen fluoride pyridine (Scheme 2). ... 

The Claisen rearrangement of lactonic enolates provides a new route to cycloalkenes. Cyclocitral was converted to the lactone (642) through a multistep sequence, the lactone deprotonated with LDA in THF at -78 °C, and the enolate quenched with f-butyldimethyl-chlorosilane (80JA6889, 6891). The crude ketene acetal (643) was heated at 110 °C for 10 h, and the product treated with fluoride ion to afford a single acid. Replacement of the quaternary carboxyl group by hydroxyl was accomplished through use of the carboxy inversion reaction (Scheme 147). The product (645) of this last reaction was identical with an authentic sample of widdrol in all respects excluding its optical rotation. 

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