ChemComm
Communication
donation of materials. The authors acknowledge the EaStCHEM
Research Computing Facility and the EPSRC National Mass
Spectrometry Service Centre, Swansea, U.K.
References
1 M. E. Jung and G. Piizzi, Chem. Rev., 2005, 105, 1735.
2 R. M. Beesley, C. K. Ingold and J. F. Thorpe, J. Chem. Soc. Trans.,
1915, 107, 1080.
3 T. C. Bruice and U. K. Pandit, J. Am. Chem. Soc., 1960, 82, 5858.
4 L. Mitchell, J. A. Parkinson, J. M. Percy and K. Singh, J. Org. Chem.,
2008, 73, 2389.
5 D. J. Nelson, I. W. Ashworth, I. H. Hillier, S. H. Kyne, S. Pandian,
J. A. Parkinson, J. M. Percy, G. Rinaudo and M. A. Vincent, Chem.–
Eur. J., 2011, 17, 13087.
6 M. D. E. Forbes, J. T. Patton, T. L. Myers, H. D. Maynard, D. W. Smith,
G. R. Schulz and K. B. Wagener, J. Am. Chem. Soc., 1992, 114, 10978.
7 T. A. Kirkland and R. H. Grubbs, J. Org. Chem., 1997, 62, 7310.
8 Y. J. Kim, J. B. Grimm and D. Lee, Tetrahedron Lett., 2007, 48, 7961.
9 S. Monfette and D. E. Fogg, Chem. Rev., 2009, 109, 3786.
10 M. S. Sanford, J. A. Love and R. H. Grubbs, J. Am. Chem. Soc., 2001,
123, 6543.
Fig. 4 Selected DFT structures (angles in degrees). Structures 2a, 2c and 2e have
C–C(5)–C angles wider than Td, whereas 2d is narrower than Td.
11 M. S. Sanford, M. Ulman and R. H. Grubbs, J. Am. Chem. Soc., 2001,
123, 749.
12 L. Cavallo, J. Am. Chem. Soc., 2002, 124, 8965.
13 C. Adlhart and P. Chen, J. Am. Chem. Soc., 2004, 126, 3496.
14 H. Clavier, C. A. Urbina-Blanco and S. P. Nolan, Organometallics,
2009, 28, 2848.
partial rotamer effect (Fig. 2). These geometries can be contrasted
with diester 2d which has a narrower C–C(CO2Me)2–C angle
(113.51). Although approaching a Td geometry, this places strain 15 C. A. Urbina-Blanco, X. Bantreil, H. Clavier, A. M. Z. Slawin and
S. P. Nolan, Beilstein J. Org. Chem., 2010, 6, 1120.
16 E. F. van der Eide and W. E. Piers, Nat. Chem., 2010, 2, 571.
17 C. A. Urbina-Blanco, A. Leitgeb, C. Slugovc, X. Bantreil, H. Clavier, A.
on the cycloheptene which compensates by ring puckering.
In conclusion, it has been observed experimentally that C5
gem-difluorination in 1c has a substantial influence on increasing
the efficiency of RCM when compared with 1a and 1b. The origin
of this effect appears to be thermodynamic and lies in the
hybridisation of the CF2 group (angle widening) which absorbs
angle strain in the cycloheptene product, as well as accommodat-
M. Z. Slawin and S. P. Nolan, Chem.–Eur. J., 2011, 17, 5045.
18 S. Manzini, C. A. Urbina-Blanco, A. M. Z. Slawin and S. P. Nolan,
Organometallics, 2012, 31, 6514.
19 C. A. Urbina-Blanco, A. Poater, T. Lebl, S. Manzini, A. M. Z. Slawin,
L. Cavallo and S. P. Nolan, J. Am. Chem. Soc., 2013, 135, 7073.
´
20 (a) M. Skibinski, Y. Wang, A. M. Z. Slawin, T. Lebl, P. Kirsch and
D. O’Hagan, Angew. Chem., Int. Ed., 2011, 50, 10581; (b) D. O’Hagan,
ing a geometry to support trans-axial hyperconjugative sCH/sCF
*
´
Y. Wang, M. Skibinski and A. M. Z. Slawin, Pure Appl. Chem., 2012,
stabilizing interactions. The stereoelectronic influences of F
extend to some extent to O in the ketal 1e/2e. It remains to be
seen if this is a general effect for all ring sizes as angle widening
84, 1587.
21 Searches of the Cambridge Structure Data Base (CSD) used the
ConQuest software. See ESI† for full details.
22 D. O’Hagan, Chem. Soc. Rev., 2008, 37, 308.
may actually destabilise other cycloalkene rings. We continue 23 J. Broggi, C. A. Urbina-Blanco, H. Clavier, A. Leitgeb, C. Slugovc, A.
M. Z. Slawin and S. P. Nolan, Chem.–Eur. J., 2010, 16, 9215.
24 C. A. Urbina-Blanco, S. Manzini, J. P. Gomes, A. Doppiu and
to explore the unique and unexpected influence of the difluor-
omethylene group on molecular properties and reactivity in
S. P. Nolan, Chem. Commun., 2011, 47, 5022.
organic transformations.
25 M. J. Frisch, et al., (see ESI†), Gaussian03, Revision D0.1, Gaussian,
Inc., Wallingford, CT, 2004.
26 (a) A. D. Becke, Phys. Rev., 1988, 38, 3098; (b) C. Lee, W. Yang and
R. G. Parr, Phys. Rev., 1988, 37, 785; (c) S. H. Vosko, L. Wilk and
M. Nusair, Can. J. Phys., 1980, 58, 1200; (d) P. J. Stephens,
F. J. Devlin, C. F. Chabalowski and M. J. Frisch, J. Phys. Chem.,
1994, 98, 11623.
SPN thanks the European Community Seventh Framework
Programme (FP7/2007–2013) under grant agreement no. CP-FP
211468-2 EUMET and the ERC (Advanced Investigator Grant-
FUNCAT) for support of this work. SPN is a Royal Society
Wolfson Research Merit Award holder. DOH thanks the ERC
27 F. Groenewald and J. Dillen, J. Struct. Chem., 2012, 23, 723.
for an Advanced Investigator Grant and is a Royal Society 28 M. K. Leong, V. S. Mastryukov and J. E. Boggs, J. Mol. Struct., 1998,
445, 149.
Wolfson Research Merit Award holder. Dr Albert Poater
and Dr David J. Nelson are greatly acknowledged for helpful
29 P. R. Rablen, R. W. Hoffmann, D. A. Hrovat and W. T. Borden,
J. Chem. Soc., Perkin Trans. 2, 1999, 1719.
discussions. Umicore is greatly acknowledged for the generous 30 P. Kirsch and M. Bremer, ChemPhysChem, 2010, 11, 357.
c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 7201--7203 7203