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E. Tayama, R. Hashimoto / Tetrahedron Letters 48 (2007) 7950–7952
The reaction of 2a in the presence of ATPH gave the
corresponding a-quaternary-b,c-unsaturated aldehyde9
6a in 97% yield [rel-(2R,20S)/rel-(2R,20R) = 6:4].10
Various types of a-quaternary-b,c-unsaturated alde-
hydes 6b–d were obtained in excellent yields with high
a-regioselectivities.11 Interestingly enough, 4-unsubsti-
tuted dienyl substrate 2g also showed an equally high
a-regioselectivity.
References and notes
1. For review: Casiraghi, G.; Zanardi, F.; Appendino, G.;
Rassu, G. Chem. Rev. 2000, 100, 1929–1972.
2. (a) Tayama, E.; Isaka, W. Org. Lett. 2006, 8, 5437–5439;
(b) Inui, M.; Hosokawa, S.; Nakazaki, A.; Kobayashi, S.
Tetrahedron Lett. 2005, 46, 3245–3248.
3. Oppolzer, W. In Comprehensive Organic Synthesis; Trost,
B. M., Ed.; Pergamon: Oxford, 1991; Vol. 5, Chapter 4.1.
4. (a) Tayama, E.; Sugai, S. Synlett 2006, 849–851; (b)
Tayama, E.; Sugai, S.; Hara, M. Tetrahedron Lett. 2006,
47, 7533–7535.
5. Prepared from tetrahydro-2-(2-propynyloxy)-2H-pyran
(50% overall yield): (i) n-BuLi, THF, ClCOOEt, ꢀ78 to
ꢀ10 °C; (ii) Me2CuLi, THF, ꢀ78 °C; (iii) Red–Al, toluene,
0 °C; (iv) MnO2, hexane, rt; (v) n-BuLi, THF, ꢀ78 °C; (vi)
NaH, MeI, THF, 0 °C to rt.
6. Prepared by Horner–Wittig reaction of trans-oct-2-en-
2-one and diethyl[(2-tetrahydropyranyloxy)methyl]phos-
phonate (45% overall yield): (i) LDA, THF, trans-oct-
3-en-2-one, ꢀ78 °C to rt; (ii) t-BuOK, THF, rt. For more
details, see Supplementary data.
7. Stewart, C. A., Jr. J. Org. Chem. 1963, 28, 3320–3323.
8. Similar yields and selectivities were observed using 3-butyl
or O-(1-ethoxyethyl) derivatives.
9. For preparations of a-quaternary-b,c-unsaturated alde-
hydes: (a) Deng, X.-M.; Sun, X.-L.; Tang, Y. J. Org.
Chem. 2005, 70, 6537–6540; (b) Mino, T.; Fukui, S.;
Yamashita, M. J. Org. Chem. 1997, 62, 734–735; (c) Hiroi,
K.; Nakazawa, K. Chem. Lett. 1980, 9, 1077–1080.
In summary, the 1,4-elimination reaction of 2-substi-
tuted-(2Z)-4-methoxy-O-alkenyl acetals with n-butyl-
lithium proceeded to yield 2-substituted-1,3-dienyl
acetals with high (1Z,3E)-stereoselectivities. Application
for the Ferrier reaction of the 2-substituted-1,3-dienyl
acetals afforded the corresponding a-quaternary-b,
c-unsaturated aldehydes in excellent yields with high
a-regioselectivities.
Acknowledgments
This work was supported by a Grant for Promotion of
Niigata University Research Projects and a Grant-in-
Aid for Scientific Research on Priority Areas ‘Advanced
Molecular Transformations of Carbon Resources’ from
the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
1
10. The relative stereochemistry of 6c was determined by H
NMR comparison with an authentic sample prepared via
diastereoselective alkylation of a-substituted-b-hydroxy-
esters. The relative stereochemistries of 6a, 6b, 6d, and 6g
were determined by analogy to the 1H NMR chemical
shifts of 6c. For more details, see Supplementary data.
11. ATPH is efficient for O-(2-tetrahydropyranyl) derivatives.
For the O-(1-ethoxyethyl) derivatives, we used MAD
because of the reasonable price. See also, Ref. 2a.
Supplementary data
Supplementary data associated with this article can be