On the preparation and unusual reactivity of a potential difluorodienophile

Tetrahedron Letters

Volumn 37, Issue 45, 1996, Pages 8233-8236

  Crowley, P J ^b   Percy, J M ^a   Stansfield, K ^a  

^a UNIVERSITY OF BIRMINGHAM   (United Kingdom)

^b JEALOTT S HILL RESEARCH STATION   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

ALKENE DERIVATIVE; ORGANOFLUORINE DERIVATIVE;

ARTICLE; DRUG SYNTHESIS; FLUORINATION; TECHNIQUE;

EID: 0000311134     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/0040-4039(96)01876-X     Document Type: Article

References (19)

1. 1. Percy, J.M. Contemporary Organic Synthesis, 1995, 4, 251-268.
2. 2. Leory, J.; Molines, H.; Wakselman, C. J. Org. Chem., 1987, 52, 290-292.
3. 3. DeCock, C.; Piettre, S.; Lahousse, F.; Janousek, Z.; Merenyi, R.; Viehe. H.G. Tetrahedron, 1985, 41, 4183-4193.
4. 4. Bartlett, P.D. Quart. Rev., 1970, 24, 473-497.
5. 5. Carr, R.V.C.; Willliams, R.V.; Paquette, L.A. J. Org. Chem., 1983, 48, 4976-4986.
6. 6 Nakai, T.; Tanaka, K.; Ogasawara, K. Chem. Lett., 1981, 1289-1292.
7. 7. Bunyagidj, C.; Pitrowska, H.; Aldridge, M.H. J. Org. Chem., 1981, 46, 3335-3336.
8. 8. McKillop, A.; Tarbin, J.A. Tetrahedron Lett., 1983, 24, 1505-1508.
9. cB character to initiate cleavage of the strong C-F bond, requiring the use of strong bases. Dehydrochlorination (and other dehydrohalogenations) are usually considerably easier to achieve. For examples, see Percy, J.M. in Comprehensive Organic Functional Group Transformations, ed. by Katritzky, A.R.; Meth-Cohn, O.; Ress, C.W. Pergamon, 1995, 1, Chapter 1.13, 570-574.
10. 4 reduction of methyl chlorodifluoroacetate.
11. 11. Kotsuki, H.; Matsumoto, K.; Nishizawa, H. Tetrahedron Lett., 1983, 32, 4155-4158
12. F-F 12.2)]. Removal of the solvent in vacuo from the crude reaction mixture gave trifluoroethyl sulfone 2a alone.
13. 13. Shi has claimed that an oxygen substituent (an alkoxy group) at the α-position stabilises β,β-difluoroalkenoates considerably; Shi, G.Q.; Cao, Z. J. Chem. Soc., Chem. Commun, 1995, 1969-1970.
14. 14 Howarth, J.A.; Owton, W.M.; Percy, J.M; Rock, M. Tetrahedron, 1995, 51, 10289-10302.
15. 15. Trost, B.M.; Mao, M.K.T. Tetrahedron Lett., 1980, 21, 3523-3526.
16. 3) or gave poor yields of sulfone (mCPBA, 44%).
17. 2S: 319.10331; found: 319.10373.
18. +). The relative stereochemistry of the cycloadduct was elucidated by an nOe experiment; irradiation of the multiplet at 4.20-4.15 resulted in positive nOe's in the two proton vinylic multiplet, and the ortho-protons in the phenylsulfonyl group, consistent with a cis arrangement between the fluorine atom and the carbamoyloxy group, and an endo orientation for the phenylsulfonyl group.
19. 19. Cyclopentadiene itself can only release hydride with the formation (formally) of an anti aromatic (4π electron) cation.