11). However, in the reaction with lithium acetylides 2b and
2d derived from enynes, the yields of the products depended
on the starting selenoamides 1 (entries 1, 7, 9, 10, 12, and
3), probably because of the stability of R,â,γ,δ-unsaturated
1
10
ketones 3. The reaction of aromatic selenoamide 1a and
R,R-disubstituted selenoamides 1g and 1h with lithium
acetylide 2b gave the corresponding products in 50-74%
yields (entries 1, 9, and 12), whereas the reaction of
R-monosubstituted selenoamide 1f gave the product 3h in
39% yield (entry 7). Furthermore, the desired products were
not obtained from the reaction of selenoamides 1d and 1e
with lithium acetylide 2b.
The â-methylselenenyl R,â-unsaturated ketones 3 were
characterized by Se NMR spectra, as shown in Table 2.
7
7
Figure 1. Ortep drawing of 3b. Hydrogen atoms are omitted for
clarity. Selected bond lengths (Å): Se1-C1, 1.892(4); Se1-C16,
1
.939(7); O1-C3, 1.217(5); C10-C15, 1.408(8); C10-C11, 1.345-
(7). Selected torsion angles (deg): Se1-C1-C10-C11, 91.8(6);
Se1-C1-C2-C3, -2.5(7); O1-C3-C2-C1, -0.7(8); O1-C3-
C4-C5-26.8(7).
Table 2. 77Se-NMR Spectra of R,â-Unsaturated Ketones 3
77Se-NMR (CDCl3) δ (ppm)
ated carbonyl unit and the cyclohexenyl plane is almost a
right angle (87.4(7)°).
entry
compound 3
Z-isomer
E-isomer
1
2
3
4
3a
3e
3f
419.6
372.6
369.4
413.1
310.5
306.4
304.2
300.1
In summary, we have demonstrated a highly efficient
conversion of selenoamides to â-methylselenenyl R,â-
unsaturated ketones by the MeOTf-mediated reaction with
lithium acetylides. Further studies should focus on the
synthetic application of the present reactions and elucidation
of their reaction pathways, which should involve several
types of new chemical species.
3g
The signals of Z-isomers of 3 were in a lower region than
those of E-isomers of 3. The results in Table 2 suggest that
the selenium atoms of Z- and E-isomers of 3 are in a different
electronic environment. To elucidate the structural features
of the products 3, an X-ray molecular structure analysis of
â-methylselenenyl R,â-unsaturated ketone 3b was carried
out. This confirmed that the product 3b had a Z-configuration
Figure 1). The intramolecular distance between the
selenium atom and the oxygen atom of the carbonyl group
was 2.74(8) Å and was within the sum of the van der Waals
Acknowledgment. This work was supported in part by
a Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
1
1
Supporting Information Available: Spectroscopic data
of 3 and tables of crystallographic data including atomic
positional and thermal parameters for 3b. This material is
available free of charge via the Internet at http://pubs/acs/org.
1
2
(
13
radii of both atoms. Accordingly, 1,5-nonbonding intra-
molecular interaction between these two atoms is present.
Additionally, the dihedral angle formed by the R,â-unsatur-
OL015968U
1
4
(
12) Crystal data of 3b: C16H18NSe, FW ) 305.28, monoclinic, space
group P21/c (No. 14), a ) 6.172(3) Å, b ) 8.825(2) Å, c ) 26.162(2) Å,
â ) 95.81(1)°, V ) 1417.6(6) Å , Z ) 4, Dcalcd ) 1.430 g‚cm , µ(Mo
KR) ) 26.35 cm , T ) 193 K, F(000) ) 624 R ) 0.110, Rw ) 0.146, R1
) 0.057, 3236 reflections (I > -10.00σ(I)), GOF ) 1.24. The position of
cyclohexenyl group is disordered: the olefinic unit should appear either
between C10 and C11 or between C10 and C15.
3
-3
-
1
(10) The introduction of a methylselenenyl group to the â-position of
R,â,γ,δ-unsaturated ketones may reduce their stability, since various R,â,γ,δ-
unsaturated ketones have been isolated in pure form: Ahlbrecht, H.; Ibe,
M. Synthesis 1988, 210-211. Herscovici, J.; Bounamaiza, L.; Antonakis,
K. Tetrahedron Lett. 1991, 32, 1791-1794. Wei, X.; Taylor, R. J. K. J.
Org. Chem. 2000, 65, 616-620. Matsubara, Y.; Yoshimatsu, M. J. Org.
Chem. 2000, 65, 4456-4459.
(13) Sum of the van der Waals radii (Å): Se‚‚‚O 3.50 Å: Nyburg, S.
C.; Faerman, C. H. Acta Crystallogr. 1985, B41, 274-279.
(14) Increasing attention has been paid to theoretical and experimental
studies on 1,5-nonbonding interaction between an oxygen atom and
chalcogen atoms because this is believed to play an important role in
defining the molecular geometry, see: Mnyeav, R. M.; Minkin, V. I. Can.
J. Chem. 1998, 76, 776-788. Nagao, Y.; Hirata, T.; Goto, S.; Sano, S.;
Kakehi, A.; Iizuka, K.; Shiro, M. J. Am. Chem. Soc. 1998, 120, 3104-
3110. Komatsu, H.; Iwaoka, M.; Tomoda, S. Chem. Commun. 1999, 205-
206. Niyomura, O.; Kato, S.; Inagaki, S. J. Am. Chem. Soc. 2000, 122,
2132-2133.
7
7
(
11) Se NMR spectra are well-known to be highly sensitive to the
electronic environment, see: Duddeck, H. Prog. NMR Spectrosc. 1995, 27,
-323. Klap o¨ tke, T. M.; Broschag, M. Compilation of Reported Se NMR
Chemical Shifts; John Wiley & Sons: New York, 1996. Wu, R.; Silks, L.
A.; Odom, J. D.; Dunlap, R. B. Spectroscopy 1996, 11, 37-42. Nakanishi,
W.; Hayashi, S. J. Phys. Chem. A 1999, 103, 6074-6081. Poleschner, H.;
Heydenreich, M.; Radeglia, R. Magn. Reson. Chem. 1999, 37, 333-345.
77
1
Org. Lett., Vol. 3, No. 13, 2001
1995