Two syntheses of 3-fluorofuran-2(5H)-one (1) based on Wittig-Horner reaction of ethyl (diethoxyphosphoryl)fluoroacetate (15) with 2-oxoethyl acetate (16) or on transformation of D-erythronolactone (10) are given. 3-Fluorofuran-2(5H)-one (1) and ethyl 2-fluorobut- 2-enoate (2) undergo conjugate addition with soft nucleophiles based on arene- carboxaldehyde dithioacetals 7 to form 2-fluorolactones 3 and 2-fluoroalkanoates 4. Intermediate enolates can be trapped in the sense of tandem addition with arenecarboxaldehydes 8 or (arylmethyl)bromides 9 to form intermediates 5 and 6 for fluorolignans. Although the conjugate addition proceeds with low stereoselectivity yielding mixture of both diastereoisomers, the electrophile in tandem addition attacks the intermediary fluoroenolate exclusively anti to its bulky β-substituent in good accord with non-fluorinated furan- 2(5H)-ones.
2-Fluoro-2-buten-4-olide, a New Fluorinated Synthon. Preparation; 1,2-1,4-, and Tandem Additions.-The title compound (VI) is prepared either from D-erythronolactone (I) or by Wittig-Horner reaction of the fluoroacetate (VII). It undergoes 1,2-addition with hard nucleophiles (X) andXII) and 1,4-addition by soft carbon nucleophile derived from (XIV) to the β-alkylated 2-fluorobutan-4-olides (XV)/(XVI). -(KVICALA, J.; PLOCAR, J.; VLASAKOVA, R.; PALETA, O.; PELTER, A.; Synlett (1997) 8, 986-988; Dep. Org. Chem., Prague Inst. Chem. Technol., CZ-166 28 Prague 6, Czech Republic; EN)
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Ixazomib citrate is a very recently approved anti-cancer drug. In all currently available literature, the molecule is characterized as containing a borate cycle formed when ixazomib is reacted with citric acid to form a stabilized ixazomib citrate that can be administered orally. However, in this work, we will show that none of the up-to-date presented structural formulas of ixazomib citrate are fully accurate. Through the combination of single-crystal and powder X-ray diffraction, solid-state NMR and DFT quantum mechanical calculations we show that, in addition to the citrate ring, another 5-membered ring is formed. These two rings are connected by the boron atom, making this compound a spirocyclic borate. We would like to acknowledge support from the Grant Agency of the Czech Republic (project no. 17-23196S).
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