Perfluorobutanesulfonyl fluoride

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Perfluorobutanesulfonyl fluoride
Nonafluorobutanesulfonyl fluoride acsformat.svg
Identifiers
Abbreviations NfF
CAS number 375-72-4
PubChem 67814
ChemSpider 61131
EC number 206-792-6
Jmol-3D images Image 1
Properties
Molecular formula C4F10O2S
Molar mass 302.09 g/mol
Density 1.682 g/mol[1]
Melting point <-120°C
Boiling point 65-66°C[2]
Related compounds
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Perfluorobutanesulfonyl fluoride (nonafluorobutanesulfonyl fluoride, NfF) is a colorless, volatile liquid that is immiscible with water but soluble in common organic solvents. It is prepared by the electrochemical fluorination of sulfolane. NfF serves as an entry point to nonafluorobutanesulfonates (nonaflates), which are valuable as electrophiles in palladium catalyzed cross coupling reactions. As a perfluoroalkylsulfonylating agent, NfF offers the advantages of lesser cost and greater stability over the more frequently used triflic anhydride. The fluoride leaving group is readily substituted by nucleophiles such as amines, phenoxides, and enolates, giving sulfonamides, aryl nonaflates, and alkenyl nonaflates respectively. However, it is not attacked by water (in which it is stable at pH<12). Hydrolysis by barium hydroxide gives Ba(ONf)2, which upon treatment with sulfuric acid gives perfluorobutanesulfonic acid and insoluble barium sulfate.

Purification[edit]

NfF purification.svg

Commercially available NfF is contaminated with 6-10 mol % perfluorosulfolane derived from its production. This is readily removed by vigorously stirring the commercial material with a concentrated aqueous solution of K3PO4 and K2HPO4 in a 1:1 molar ratio for 96 hours. This treatment, followed by removal of the aqueous layer and distillation from P2O5, gives a product that contains >99 mol % NfF with near quantitative recovery.[3]

Synthesis of aryl and alkenyl nonaflates[edit]

As mentioned above, aryl and alkenyl nonaflates are useful as electrophiles in palladium catalyzed cross coupling reactions. Their reactivity generally mirrors that of the more commonly encountered triflate electrophiles, but nonaflates tend to be less prone to hydrolysis to ketones (in the case of alkenyl sulfonates) and phenols (in the case of aryl sulfonates). Their resistance to hydrolysis makes nonaflates superior electrophiles in Buchwald-Hartwig couplings, where this side reaction can be deleterious to yields of the desired product.[4]

The sodium enolates of β-ketoesters react with 1.15 equivalents of NfF to give the corresponding alkenyl nonaflates in high yield. Ethyl 2-methylacetoacetate (R=R'=Me) gives the geometrically pure E isomer by this method.[5]

Nonaflates from beta keto esters.gif

Simple aldehydes and ketones react with NfF in the presence of bases such as DBU or phosphazenes to give alkenyl nonaflates in high yields without formation of a discrete enolate. Use of the P2 phosphazene base at -30 to -20°C gives the less substituted alkenyl nonaflate with unsymmetrically substituted ketones.[3] Similar reactions with triflic anhydride generally require the use of the expensive 2,6-di-tert-butylpyridine to achieve high yields.

The reaction of enolates with NfF depends strongly both on the structure of the enolate and its metal counterion. The lithium enolates of methyl ketones give mixtures of products derived from electrophilic attack on the O (expected) or C (unexpected) atoms of the enolate. This effect is particularly evident with the lithium enolate of pinacolone, which gives a 2:1 mixture favoring C-attack. More substituted lithium enolates give only products of O sulfonylation in variable yields.[6]

Pinacolone lithium enolate nonaflation correction.gif

Trimethylsilyl enol ethers react with NfF in the presence of a substoichiometric fluoride source at 0°C to ambient temperature to give alkenyl nonaflates in moderate to good yields. Dried Bu4F was the preferred fluoride source in one study,[6] but CsF has been used in difficult cases with excellent results.[7]

Bis alkenyl nonaflate formation from silyl enol ether.png

Aryl nonaflates can be prepared straightforwardly from phenols and NfF in the presence of bases such as potassium carbonate[8] and Et3N[4] in near quantitative yields. Stronger bases such as NaH and BuLi[9] can also be used, but they tend to give somewhat lower yields.

Reaction With Alcohols[edit]

The reaction of NfF with alcohols highlights the lability of alkyl nonaflates – in most cases, the final product of the reaction is either an alkyl fluoride (from F- attack on the intermediate alkyl nonaflate) or an olefin (from elimination of NfOH from the intermediate nonaflate).

Synthesis of bis-nonafluorobutanesulfonimide (Nf2NH)[edit]

NfF reacts with ammonium chloride in the presence of triethylamine in acetonitrile to give the triethylammonium salt of the superacidic bis-nonafluorobutanesulfonimide in 97% yield. The corresponding potassium salt is obtained by treatment of a methanolic solution of the triethylammonium salt with KOH.[10] The acid is obtained by ion exchange chromatography of the triethylammonium salt with Amberlite IR-100 as the stationary phase and methanol as the eluent.[11] The actual species produced in the latter procedure is likely MeOH2+ Nf2N-.

References[edit]

  1. ^ "Perfluoro-1-butanesulfonyl fluoride". Retrieved 22 July 2012. 
  2. ^ "1,1,2,2,3,3,4,4,4-nonafluorobutane-1-sulphonyl fluoride". National Institute of Standards and Technology. Retrieved 22 July 2012. 
  3. ^ a b Vogel, Michael A. K.; Christian B. W. Stark; Ilya M. Lyapkalo (2007). "A Straightforward Synthesis of Alkenyl Nonaflates from Carbonyl Compounds Using Nonafluorobutane-1-sulfonyl Fluoride in Combination with Phosphazene Bases". Synlett 2007 (EFirst): 2907–2911. doi:10.1055/s-2007-991084. ISSN 0936-5214. 
  4. ^ a b Meadows, Rebecca E.; Simon Woodward (2008-02-11). "Steric effects in palladium-catalysed amination of aryl triflates and nonaflates with the primary amines PhCH(R)NH2 (R=H, Me)". Tetrahedron 64 (7): 1218–1224. doi:10.1016/j.tet.2007.11.074. ISSN 0040-4020. 
  5. ^ Bellina, Fabio; Donatella Ciucci; Renzo Rossi; Piergiorgio Vergamini (1999-02-12). "Synthesis of vinyl nonaflates derived from β-ketoesters, β-diketones or α-diketones and their palladium-catalyzed cross-coupling reactions with organozinc halides". Tetrahedron 55 (7): 2103–2112. doi:10.1016/S0040-4020(98)01221-6. ISSN 0040-4020. 
  6. ^ a b Lyapkalo, Ilya M.; Matthias Webel, Hans-Ulrich Reißig (2002). "An Expedient and Stereoselective Synthesis of Alkenyl Nonaflates from Silyl Enol Ethers: Optimization, Scope and Limitations". European Journal of Organic Chemistry 2002 (6): 1015–1025. doi:10.1002/1099-0690(200203)2002:6<1015::AID-EJOC1015>3.0.CO;2-K. ISSN 1099-0690. 
  7. ^ Bräse, Stefan (1999). "Synthesis of Bis(enolnonaflates) and their 4-exo-trig-Cyclizations by Intramolecular Heck Reactions". Synlett 1999 (10): 1654–1656. doi:10.1055/s-1999-2892. ISSN 0936-5214. 
  8. ^ Shekhar, Shashank; Travis B. Dunn; Brian J. Kotecki; Donna K. Montavon; Steven C. Cullen (2011). "A General Method for Palladium-Catalyzed Reactions of Primary Sulfonamides with Aryl Nonaflates". J. Org. Chem. 76 (11): 4552–4563. doi:10.1021/jo200443u. ISSN 0022-3263. 
  9. ^ Uemura, Minoru; Hideki Yorimitsu; Koichiro Oshima (2008-02-18). "Cp∗Li as a base: application to palladium-catalyzed cross-coupling reaction of aryl-X or alkenyl-X (X=I, Br, OTf, ONf) with terminal acetylenes". Tetrahedron 64 (8): 1829–1833. doi:10.1016/j.tet.2007.11.095. ISSN 0040-4020. 
  10. ^ Quek, Ser Kiang; Ilya M. Lyapkalo; Han Vinh Huynh (2006-03-27). "Synthesis and properties of N,N′-dialkylimidazolium bis(nonafluorobutane-1-sulfonyl)imides: a new subfamily of ionic liquids". Tetrahedron 62 (13): 3137–3145. doi:10.1016/j.tet.2006.01.015. ISSN 0040-4020. 
  11. ^ Hashmi, A. Stephen K.; Tobias Hengst; Christian Lothschütz; Frank Rominger (2010). "New and Easily Accessible Nitrogen Acyclic Gold(I) Carbenes: Structure and Application in the Gold-Catalyzed Phenol Synthesis as well as the Hydration of Alkynes". Advanced Synthesis & Catalysis 352 (8): 1315–1337. doi:10.1002/adsc.201000126. ISSN 1615-4169.