A New Method for the Synthesis of α,α-Difluoro-β-hydroxy Esters through the Enolization of S-tert-Butyl Difluoroethanethioate

Optimized Synthesis of a Pentafluoro-gem-diol and Conversion to a CF2Br-Glucopyranose through Trifluoroacetate-Release and Halogenation

Pentafluoro-gem-diols are substrates that enable the synthesis of valuable difluoromethylene-containing organic molecules through the release of trifluoroacetate. Currently, only one synthetic strategy is available to assemble these important precursors. Herein, two new synthetic strategies to a complex pentafluoro-gem-diol are compared to the existing route, and an improved synthetic route has completed. Moreover, the first synthesis of a CF₂Br-glucopyranose was finished by a tandem trifluoroacetate-release halogenation/cyclization protocol.

Fluorinated enol ethers: their synthesis and reactivity

This review sums up the methods for the preparation of fluorinated enol ethers as well as their numerous synthetic applications.

The synthesis of gemcitabine

Gemcitabine is a fluorinated nucleoside currently administered against a number of cancers. It consists of a cytosine base and a 2-deoxy-2,2-difluororibose sugar. The synthetic challenges associated with the introduction of the fluorine atoms, as well as with nucleobase introduction of 2,2-difluorinated sugars, combined with the requirement to have an efficient process suitable for large scale synthesis, have spurred significant activity towards the synthesis of gemcitabine exploring a wide variety of synthetic approaches. In addition, many methods have been developed for selective crystallisation of diastereomeric (including anomeric) mixtures. In that regard, the 2-deoxy-2,2-difluororibose sugar is one of the most investigated fluorinated carbohydrates in terms of its synthesis. The versatility of synthetic methods employed is illustrative of the current state of the art of fluorination methodology for the synthesis of CF2-containing carbohydrates, and involves the use of fluorinated building blocks, as well as nucleophilic and electrophilic fluorination of sugar precursors.

Synthesis of α-halo-α,α-difluoromethyl ketones by a trifluoroacetate release/halogenation protocol

Three series of α-halo-α,α-difluoromethyl ketones are prepared from highly α-fluorinated gem-diols by exploiting the facile release of trifluoroacetate, followed by immediate trapping of the liberated α,α-difluoroenolate with an electrophilic chlorine, bromine, or iodine source. The products are typically isolated in good yields, even in the case of sensitive, α-iodo-α,α-difluoromethyl ketones. Also, we demonstrate that an α-iodo-α,α-difluoromethyl ketone will participate in a copper-promoted reaction to forge a new carbon-carbon bond.

Cleavage of carbon-carbon bonds through the mild release of trifluoroacetate: generation of α,α-difluoroenolates for aldol reactions

The selective cleavage of carbon-carbon bonds is a significant challenge in synthetic chemistry, yet this strategy can be a powerful way to generate reactive intermediates. We have discovered that, through the facile release of trifluoroacetate which occurs by C-C bond scission, difluoroenolates can be generated under very mild reaction conditions. Unlike existing reactions, this method is not limited to a small group of fluorinated building blocks. We have applied this process to the aldol reaction to install difluoromethylene groups.

New and Efficient Syntheses of α-Iodo-α,α-Difluoro- and β-Iodo-α,α,β,β-Tetrafluorocarboxylic Acid Derivatives as Useful Building Blocks for Making Functional Fluoro Compounds

Perfluoroolefins reacted with I-Cl and ClSO(3)H under mild conditions to give R(F)CFICF(2)OSO(2)Cl, which could be readily converted into various alpha-iodo-perfluorocarboxylic acid derivatives or telomerized with tetrafluoroethylene to I(CF(2)CF(2))(n)()OSO(2)Cl. Ring-opening reaction of perfluoroalkoxypentafluorocyclopropane with iodine at 240 degrees C produced ICF(2)CF(2)COF, which was quenched by alcohol, water, or NH(3) to give beta-iodo-alpha,alpha,beta,beta-tetrafluorocarboxylic acid derivatives. These functional fluorinated iodides can be used as building blocks for making selectively fluorinated compounds.

Electroreductive Defluorination of Trifluoromethyl Ketones and Trifluoroacetic Acid Derivatives

Difluoroenol silyl ethers 5 and 6, difluoroketene silyl (O,O-, O,S-, and O,N-) acetals 9 and 21, and 2,2-difluoro-2-trimethylsilylacetates 10 were prepared by electroreductive defluorination of trifluoromethyl ketones and trifluoroacetic acid derivatives in an MeCN-TBAB-chlorotrialkylsilane system using a carbon rod as an anode and a lead plate as a cathode. TBAF- or KF-CuI-promoted alpha-alkylation of 10 with electrophiles such as aldehydes, ketones, imine, acylhalides, and alkylhalides provided alpha-alkylated-alpha,alpha-difluoroacetates in good to excellent yields.