ORGANIC
LETTERS
2007
Vol. 9, No. 13
2549-2552
Ring-Closing Reaction of Allenic/
Propargylic Anions Generated by Base
Treatment of Sulfonylallenes
Shinji Kitagaki, Satoshi Teramoto, and Chisato Mukai*
DiVision of Pharmaceutical Sciences, Graduate School of Natural Science and
Technology, Kanazawa UniVersity, Kakuma-machi, Kanazawa 920-1192, Japan
Received April 20, 2007
ABSTRACT
The intramolecular trapping of allenyl/propargyl anions generated by base treatment of sulfonylallenes was investigated. Treatment of 1-(
iodoalkyl)-1-(phenylsulfonyl)allenes with TBAF or NaH in DMF efficiently produced three- to seven-membered 1-ethynyl-1-(phenylsulfonyl)
substituted carbocycles. The allenyl/propargyl anions could also be intramolecularly trapped using a terminal aldehyde or -unsaturated
ω-
r,â
ester. The phenylsulfonyl group was found to be replaced by other electron-withdrawing functionalities like ketone and ester groups but not
by an alkyl group for this novel ring-closing reaction.
It is well-known that the γ-proton of an allyl functionality
possessing an electron-withdrawing group (EWG) at the
R-position is acidic enough to be abstracted by strong amide
bases, such as lithium diisopropylamide (LDA), at low
temperature. The allyl anion species, thus generated, could
be used for a variety of carbon-carbon bond formations,
exemplified by the vinylogous aldol reaction, in organic
synthesis.1 On the other hand, the γ-allenic proton having
an EWG at the R-position, namely the proton of the sp2-
hybridized carbon of the 1-EWG-allene species, would be
anticipated to be more acidic than that of the sp3-hybridized
carbon of the 1-EWG-allyl species owing to the following
two factors. One is that the C-H σ bond of the γ-carbon is
strictly eclipsed by the π bond between the R- and â-carbons,
thereby introduction of an EWG at the R-position would
markedly increase its acidity, and the other factor is an
inherently higher s character of the allenic γ-carbon (sp2-
hybridized carbon) than the allylic carbon (sp3-hybridized
carbon).
As a part of our studies2 on the development of novel and
efficient methods for ring-closing reactions by taking ad-
vantage of the intrinsic property of allenes, we have dem-
onstrated that allenes 1 having an EWG and an ω-hydroxy-
alkyl group at the same allenic terminus easily underwent
the endo-dig mode ring-closing reaction to produce the five-
to eight-membered oxacycles 2 (Scheme 1).2a,f,n We now
envisaged, on the basis of the above prediction regarding
the acidity of the γ-allenic proton having an EWG at the
R-position, that replacing the terminal hydroxy group of 1
(2) (a) Mukai, C.; Yamashita, H.; Hanaoka, M. Org. Lett. 2001, 3, 3385-
3387. (b) Mukai, C.; Nomura, I.; Yamanishi, K.; Hanaoka, M. Org. Lett.
2002, 4, 1755-1758. (c) Mukai, C.; Ukon, R.; Kuroda, N. Tetrahedron
Lett. 2003, 44, 1583-1586. (d) Mukai, C.; Inagaki, F.; Yoshida, T.; Kitagaki,
S. Tetrahedron Lett. 2004, 45, 4117-4121. (e) Mukai, C.; Kobayashi, M.;
Kubota, S.; Takahashi, Y.; Kitagaki, S. J. Org. Chem. 2004, 69, 2128-
2136. (f) Mukai, C.; Ohta, M.; Yamashita, H.; Kitagaki, S. J. Org. Chem.
2004, 69, 6867-6873. (g) Mukai, C.; Kuroda, N.; Ukon, R.; Itoh, R. J.
Org. Chem. 2005, 70, 6282-6290. (h) Mukai, C.; Takahashi, Y. Org. Lett.
2005, 7, 5793-5796. (i) Kitagaki, S.; Ohdachi, K.; Katoh, K.; Mukai, C.
Org. Lett. 2006, 8, 95-98. (j) Inagaki, F.; Mukai, C. Org. Lett. 2006, 8,
1217-1220. (k) Kuroda, N.; Takahashi, Y.; Yoshinaga, K.; Mukai, C. Org.
Lett. 2006, 8, 1843-1845. (l) Kitagaki, S.; Okumura, Y.; Mukai, C.
Tetrahedron Lett. 2006, 47, 1849-1852. (m) Mukai, C.; Itoh, R. Tetra-
hedron Lett. 2006, 47, 3971-3974. (n) Kitagaki, S.; Shibata, D.; Mukai,
C. Tetrahedron Lett. 2007, 48, 1735-1738.
(1) For reviews, see: (a) Denmark, S. E.; Heemstra, J. R., Jr.; Beutner,
G. L. Angew. Chem., Int. Ed. 2005, 44, 4682-4698. (b) Kalesse, M. Top.
Curr. Chem. 2005, 244, 43-76. (c) Casiraghi, G.; Zanardi, F.; Appendino,
G.; Rassu, G. Chem. ReV. 2000, 100, 1929-1972.
10.1021/ol0709329 CCC: $37.00
© 2007 American Chemical Society
Published on Web 05/19/2007