ORGANIC
LETTERS
2002
Vol. 4, No. 15
2565-2567
Synthesis of New Heterocycles through
a Cation-Driven Tandem
Ring-Enlargement−Annulation Reaction
Angela M. Bernard,* Enzo Cadoni, Angelo Frongia, Pier P. Piras,* and
Francesco Secci
Dipartimento di Scienze Chimiche, UniVersita` degli studi di Cagliari,
Cittadella UniVersitaria di Monserrato, S.S 554, BiVio per Sestu,
I-09042 Monserrato (Cagliari), Italy
Received May 17, 2002
ABSTRACT
The thionium ion, generated through a cyclopropylcarbinyl-cyclobutyl ring expansion, is, for the first time, intramolecularly intercepted by
activated aromatic rings to generate new versatile 2a-methyl-8b-(phenylsulfanyl-1,2a,3,8b-tetrahydro-2H-cyclobuta[c]chromenes.
Rearrangements involving the cyclopropyl group of properly
substituted cyclopropanes are well-known in organic syn-
thesis as they represent a practical access to ring-opened
products or to carbo- and heterocyclic derivatives.1 If the
cyclopropanes bear an electron-donor substituent (O, S, N)
and an electron-deficient center on the same atom, they
undergo ring expansion to give cyclobutanones,1-3 through
a transformation closely related to the Wagner-Merwein
rearrangement. Among the different ways of accomplishing
this transformation, particularly important is the reaction with
acids of the cyclopropylcarbinols obtained from the reaction
of the metalated cyclopropyl phenyl sulfide with carbonyl
partners.3b,4,5
(1) (a) Salaun, J. In The Chemistry of the Cyclopropyl Group; Patai, S.,
Rappoport, Z., Eds.; Wiley and Sons: New York, 1987; Vol. 2, pp 809-
878. (b) Reissig, H.-Ulrich In The Chemistry of the Cyclopropyl Group;
Patai, S., Rappoport, Z., Eds.; Wiley and Sons: New York, 1987; Vol. 1,
pp 375-443. (c) Hardouin, C.; Taran, F.; Doris, E. J. Org. Chem. 2001,
66, 4450.
The reaction is believed to proceed through a cyclobutyl
R-thiocarbocation to give the cyclobutanone. The first and
only example of intramolecular interception of the thionium
(2) For a review on cyclobutanones and cyclobutenones, see: Bellus,
D.; Ernst, B. Angew. Chem., Int. Ed. Engl. 1988, 27, 797.
(3) (a) Salaun, J. Top. Curr. Chem. 1988, 144, 1. (b) Trost, B. M. Top.
Curr. Chem. 1986, 133, 3. (c) Nemoto, H.; Ishibashi, H.; Mori, M.; Fujita,
S.; Fukumoto, K. J. Chem. Soc., Perkin Trans. 1 1990, 2835. (d) Nemoto,
H.; Yamada, T.; Ishibashi, H.; Fukumoto, K. J. Chem. Soc., Perkin Trans.
1 1991, 3149. (e) Nemoto, H.; Ishibashi, H.; Nagamochi, M.; Fukumoto,
K. J. Org. Chem. 1992, 57, 1707. (f) Nemoto, H.; Yamada, T.; Ishibashi,
H.; Takazawa, J.; Fukumoto, K. Heterocycles 1991, 32, 863. (g) Nemoto,
H.; Tanabe, T.; Nagamochi, M.; Fukumoto, K. Heterocycles 1993, 35, 707.
(h) Nemoto, H.; Shiraki, M.; Fukumoto, K. Tetrahedron 1994, 50, 10391.
(i) Nemoto, H.; Miyata, J.; Hakamata, H.; Nagamochi, M.; Fukumoto, K.
Tetrahedron 1995, 51, 5511. (j) Krief, A.; Ronvaux, A.; Tuch, A. Bull.
Soc. Chim. Belg. 1997, 106, 699. (k) Diffendal, J. M.; Filan, J.; Spoors, P.
G. Tetrahedron Lett. 1999, 40, 6137. (l) Chevtchouk, T.; Ollivier, J.; Salaun,
J. Tetrahedron: Asymmetry 1997, 8, 1011. (m) Bernard, A. M.; Floris, C.;
Frongia, A.; Piras, P. P. Tetrahedron 2000, 56, 4555. (n) Youn, J.-H.; Lee,
J.; Cha, J. K. Org. Lett. 2001, 3, 2935.
(4) (a) Trost, B. M.; Keeley, D. E. J. Org. Chem. 1975, 40, 2013. (b)
Trost, B. M.; Keeley, D. E.; Arndt, H. C.; Bogdanowicz, M. J. J. Am Chem
Soc. 1977, 99, 3088. (c) Trost, B. M.; Jungheim, L. N. J. Am Chem Soc.
1980, 102, 7910. (d) Trost, B. M.; Ornstein, P. L. J. Org. Chem. 1983, 48,
1131.
(5) A potential severe limitation of this approach is that the starting
cyclopropylcarbinols are only available from cyclopropyl phenyl sulfide
itself and its 2-hydroxymethyl derivative. The presence of other substituents
on the cyclopropyl ring makes proton removal extremely difficult or
impossible. The solution of this problem has been found by Cohen by
producing 1-phenylthiocyclopropyl carbinols, containing several arrange-
ments of substituents on the cyclopropyl ring, by reaction of 1-lithio-1-
phenylthiocyclopropane generated by reductive lithiation of the correspond-
ing 1,1-bis-phenylthiocyclopropane. Cohen, T.; Daniewski, W. M.; Weisenfeld,
R. B. Tetrahedron Lett. 1978, 4665. Cohen, T.; Weisenfeld, R. B.; Gapinski,
R. E. J. Org. Chem. 1979, 44, 4744.
10.1021/ol026199x CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/27/2002