Despite the growing importance of organofluorines as pharmaceuticals and agrochemicals, the stereoselective introduction of fluorine into many prominent classes of natural products and chemotherapeutic agents is difficult. One long-standing unsolved challenge is the enantioselective aldol reaction of fluoroacetate to enable access to fluorinated analogues of medicinally relevant acetate-derived compounds, such as polyketides and statins. Herein we present fluoromalonic acid halfthioesters as biomimetic surrogates of fluoroacetate and demonstrate their use in highly stereoselective aldol reactions that proceed under mild organocatalytic conditions. We also show that the methodology can be extended to formal aldol reactions with fluoroacetaldehyde and consecutive aldol reactions. The synthetic utility of the fluorinated aldol products is illustrated by the synthesis of a fluorinated derivative of the top-selling drug atorvastatin. The results show the prospects of the method for the enantioselective introduction of fluoroacetate to access a wide variety of highly functionalized fluorinated compounds.
α-Fluorinated β-amino thioesters were obtained in high yields and stereoselectivities by organocatalyzed addition reactions of α-fluorinated monothiomalonates (F-MTMs) to N-Cbz- and N-Boc-protected imines. The transformation requires catalyst loadings of only 1 mol % and proceeds under mild reaction conditions. The obtained addition products were readily used for coupling-reagent-free peptide synthesis in solution and on solid phase. The α-fluoro-β-(carb)amido moiety showed distinct conformational preferences, as determined by crystal structure and NMR spectroscopic analysis.
Double‐action haloketones: A super silyl group enabled the first highly diastereoselective Mukaiyama aldol reactions of α‐chloro‐ and α‐fluoroketones with a wide range of aldehydes, providing anti‐β‐siloxy‐α‐haloketones. This process is compatible with one‐pot double‐aldol methodology and allows for rapid access to new halogen‐modified polyketide fragments bearing up to four contiguous stereocenters (see scheme).
The Mukaiyama cross aldol reaction of α-fluoro-, α-chloro-, and α-bromoacetaldehyde-derived (Z)-tris(trimethylsilyl)- silyl enol ethers furnishing anti-β-siloxy-α-haloaldehydes is described. A highly diastereoselective, one-pot, sequential double aldol process, affording novel β,δ-bissiloxy-α,γ-bishaloaldehydes is developed. Reactions are catalyzed by C6F5CHTf2 and C6F5CTf2AlMe2 (0.5–1.5 mol%) and provide access to halogenated polyketide fragments.
Fluorinated monothiomalonates (F-MTMs) were used as building blocks for the stereoselective synthesis of organofluorine compounds. We present conjugate addition reactions between F-MTMs with nitroolefins that proceed under mild organocatalytic conditions and provide access to α-fluoro-γ-nitro thioesters with adjacent tetrasubstituted and tertiary stereogenic centers. Only 1 mol % of a cinchona alkaloid-urea catalyst is necessary to obtain the addition products in excellent yields and stereoselectivities. The methodology allowed for the straightforward synthesis of a fluorinated analogue of the PAR-2 agonist AC-264613.
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