This work was supported by Crompton Co., the Natural
Sciences and Engineering Research Council of Canada (NSERC),
the Ontario Research and Development Challenge Fund, and the
Environmental Science and Technology Alliance of Canada. We
thank Dr A. B. Young for mass spectrometric analysis, Dr
T. Burrow for help with NMR analysis, and Dr A. J. Lough for
X-ray crystallographic analysis of compound 4d.
Notes and references
§ CCDC 651248. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b709337n
Scheme 2 Bellus ketene-Claisen type rearrangement of 9.
1
J. Stenhouse, Justus Liebigs Ann. Chem., 1850, 74, 278.
transition state for the formation of cis-4 from 8-ZEZZ is
2 (a) J. Becher, Synthesis, 1980, 589–612; (b) W.-C. Cheng and M. J. Kurth,
Org. Prep. Proc. Intl., 2002, 34, 585–608.
21
disfavored by 10.4 kcal mol over that for the trans closure. These
computational results support a ‘‘Nazarov-like’’ mechanism, and
the trans-stereochemistry of 4 is consistent with the Woodward–
Hoffmann rules. Similar electrocyclization mechanisms have
also been proposed for the acid promoted conversion of 2-furyl-
3
(a) M. D’Ambrosio, A. Guerriero, C. Debitus, O. Ribes, J. Pusset,
S. Leroy and F. Pietra, J. Chem. Soc., Chem. Commun., 1993,
1305–1306; (b) M. D’Ambrosio, A. Guerriero, G. Chiasera and
F. Pietra, Helv. Chim. Acta, 1994, 77, 1895–1902; (c) M. D’Ambrosio,
A. Guerriero, M. Ripamonti, C. Debitus, J. Waikedre and F. Pietra,
Helv. Chim. Acta, 1996, 79, 727–735.
1
0
carbinols into 4- hydroxycyclopentenones. While the computa-
tional results provide insight into the stereodetermining step of
the reaction, further mechanistic studies are necessary before a
definitive mechanism for the overall reaction pathway can be
established.
4
See: (a) F. A. Davis and J. Deng, Org. Lett., 2005, 7, 621–623; (b)
M. M. Domostoj, E. Irving, F. Scheinmann and K. J. Hale, Org. Lett.,
2004, 6, 2615–2618 and references cited.
5 For a general review on the chemistry of Stenhouse salts and their
derivatives, including the formation of 4 and 5, see: K. G. Lewis and
C. E. Mulquiney, Tetrahedron, 1977, 33, 463–475.
The 4,5-diaminocyclopent-2-enone products 4 are versatile
synthetic equivalents for the formation of densely functionalized
derivatives. For example, Luche reduction of 4a followed by
benzyl protection affords 9, which was subjected to a Bellus
ketene-Claisen type rearrangement using MacMillan’s condi-
6
(a) E. S. Nicholson and B. T. Ashworth, (Imperial Chemical Industries
Ltd., Engl.) U.S. Patent 4013720, 19770722, 1977; (b) K. G. Lewis and
C. E. Mulquiney, Aust. J. Chem., 1979, 32, 1079–1092; (c) T. Hofmann,
J. Agric. Food Chem., 1998, 46, 932–940.
(a) J. C. McGowan, J. Chem. Soc., 1949, 777–779; (b) J. Rombaut and
G. Smets, Bull. Soc. Chim. Belg., 1949, 58, 421–431; (c) J. C. McGowan,
J. Chem. Soc., 1954, 4032–4034; (d) K. G. Lewis and C. E. Mulquiney,
Aust. J. Chem., 1970, 23, 2315–2323.
D. A. Powell and R. A. Batey, Tetrahedron Lett., 2003, 44, 7569–7573.
Ring-opening of intermediate 7 would presumably lead to 8 as the
ZZZE isomer. Isomerization of 8-ZZZE to 8-ZEZE (as depicted in
Scheme 1) would be necessary before cyclization to 4 could occur.
7
11
tions, to give 10 as a single diastereomer (Scheme 2).
In conclusion, the first practical preparation of 4,5-diamino-
cyclopent-2-enones 4 from 2-furaldehyde and secondary amines by
Ln(III) and Sc(III) catalysis has been developed. The products 4 are
exclusively formed as the trans-diastereomers, consistent with a
thermal conrotatory p4a electrocyclization, reminiscent of the
8
9
10 G. Piancatelli, A. Scettri, G. David and M. D’Auria, Tetrahedron, 1978,
34, 2775–2778; for a review see: G. Piancatelli, M. D’Auria and
F. D’Onofrio, Synthesis, 1994, 867–889.
1
2
Nazarov cyclization. Further studies and applications on this
remarkable domino ring-opening electrocyclization process of
1
1 T. P. Yoon, V. M. Dong and D. W. C. MacMillan, J. Am. Chem. Soc.,
999, 121, 9726–9727.
12 A. J. Frontier and C. Collison, Tetrahedron, 2005, 61, 7577–7606.
2-furaldehyde to cyclopentanoid synthesis and manipulations of
1
Stenhouse salts will be reported in due course.
This journal is ß The Royal Society of Chemistry 2007
Chem. Commun., 2007, 3759–3761 | 3761