Chemistry Letters Vol.36, No.9 (2007)
1181
References and Notes
1
for the present RCM, while the syn/anti selectivity is different
between the two RCMs.
For recent reviews of molecular machines, see: V. Balzani, M.
Venturi, A. Credi, Molecular Devices and Machines, Wiley-VCH
Verlag, Weinheim, Germany, 2003; Molecular Machines. Topics
in Current Chemistry, ed. by T. R. Kelley, Springer, Berlin,
Heidelberg, New York, 2005; V. Balzani, A. Credi, F. M. Raymo,
W. Setaka, K. Sato, A. Ohkubo, C. Kabuto, M. Kira, Chem. Lett.
The 1,10-bridging of a 1,10-dibromo-1,4,7,10,13,16-hexasilacyclo-
octadecane with the di-Grignard reagent derived from 1,12-dibro-
mododecane but the reaction gave desired compounds only in
1.5% yield: E. Kwon, K. Sakamoto, C. Kabuto, M. Kira, Silicon
Me
I
Me
I
Me
Si
Si
Si
Si
Si
Grubbs' cat.
I
TsNHNH2
(1)
CH2Cl2, Reflux
Diglyme, Reflux
I
I
I
Si
Me
2
Me
Me
5d
E/Z-mixture of 8d, 85%
9d, 96%
3
4
It is an interesting issue whether halogen substituents in the
highly congested environment of 6a and 6b are replaced by other
substituents. The iodine substituents of anti,E,E-6b were easily
removed by tert-butyllithium to give the corresponding dehalo-
genated macrocycle anti,E,E-6d after hydrolysis (eq 2), while
the debromination reaction of anti,E,E-6a with t-BuLi was in-
complete.9 The Sonogashira coupling reactions11 of anti,E,E-
6a and anti,E,E-6b with phenylacetylene did not proceed
(eq 3),12 suggesting severe steric hindrance during the reactions.
5
6
7
a) T. Shima, E. B. Bauer, F. Hampel, J. A. Gladysz, Dalton Trans.
For recent reviews of RCM, see: R. H. Grubbs, S. Chang, Tetra-
39, 3012.
¨
A mixture of 5a (0.628 g, 0.96 mmol), Grubbs’ catalyst, 1st genera-
tion (0.04 g, 5 mol %), and dichloromethane (200 mL) was refluxed
at 50 ꢁC for 7 h. Removal of solvent in vacuo, silica-gel column
chromatography using toluene eluent, and then repeated washing
with hexane afforded anti,E,E-6a (0.20 g, 32% yield) as colorless
crystals. Similar reactions of 5b afforded anti,E,E-6b in 23% yield.
anti,E,E-6a: mp: 260–261 ꢁC; 1H NMR (400 MHz, CDCl3, 298 K) ꢁ
0.36 (s, 6H, SiCH3), 0.55–1.77 (m, 32H, CH2), 4.88 (t, 4H, CH=,
J ¼ 3:6 Hz), 7.48 (s. 2H, PhH); 13C NMR (100 MHz, CDCl3)
ꢁ ꢂ 3:78, 12.78, 23.96, 31.22, 32.38, 129.87, 130.05, 140.31,
144.30; 29Si NMR (79 MHz, CDCl3) ꢁ 4.48 (SiMe); Anal. Calcd
for C28H44Br2Si2 (MW: 596.63): C, 56.37; H, 7.43%. Found: C,
56.33; H, 7.53%. anti,E,E-6b: mp: 278–279 ꢁC; 1H NMR
(400 MHz, CDCl3, 298 K) ꢁ 0.37 (s, 6H, SiCH3), 0.51–1.80 (m,
32H, CH2), 4.90 (t, 4H, CH=, J ¼ 3:6 Hz), 7.73 (s, 2H, PhH);
13C NMR (100 MHz, CDCl3) ꢁ ꢂ 3:27, 12.22, 24.08, 31.19, 32.49,
105.87, 129.87, 147.86, 148.52; 29Si NMR (79 MHz, CDCl3) ꢁ
5.61 (SiMe). Anal. Calcd for C28H44I2Si2 (MW: 690.63): C,
48.69; H, 6.42%. Found: C, 48.76; H, 6.50%.
Me
1) t-BuLi, Pentane/
Si
THF
anti,E,E-6b
(2)
2) H2O
Si
anti,E,E-6d,
29% yield
Me
Me
Ph
Si
anti,E,E-6a
Ph
H
(3)
(or anti,E,E-6b)
Sonogashira
Coupling
Si
Ph
10
Me
Molecular structures of anti,E,E isomers of 6a, 6b, and 6d,
syn,E,E-6b, anti-7c, and 9d were determined by X-ray crystal-
lography.9,13 The X-ray structure of 6a is shown in Figure 1.
The phenylene planes of anti,E,E isomers of 6a, 6b, and 6d
are roughly perpendicular to the averaged plane of disilacycloal-
kadiene ring probably to minimize the steric contact between the
macro-ring and the phenylene rings. The most stable phenylene
ring conformation seems to be kept also in solution, because the
alkene proton chemical shifts for anti,E,E isomers of 6a, 6b, and
6d (4.74–4.90 ppm) are relatively lower than those of simple
alkenes [5.5 ppm for (E)-2-butene].14
8
9
Very small amounts of syn-E,E isomers of 6a and 6b (0.5% for each)
were isolated through recycled HPLC among the mixture.9
See Supporting Information available electronically on the CSJ-
10 For hydrogenation of sila-macrocycles using tosylhydrazine, see: E.
Kwon, K. Sakamoto, C. Kabuto, M. Kira, Chem. Lett. 2000, 1416.
For full characterization of 7a–7c, see Supporting Information.9
11 For a recent review of Sonogashira coupling reactions, see: R.
12 The Sonogashira coupling reactions of anti,E,E-6a, anti,E,E-6b,
and anti-7a and anti-7b using Pd[PPh3]4, Pd[PPh3]2Cl2, Pd[P(t-
Bu)3]2Cl2, or PdCl2 were unsuccessful. No reaction occurred be-
tween anti,E,E-6a (or anti,E,E-6b) and cuprous phenyl acetylide.
However, the Sonogashira coupling reactions of 5a and 5b with
trimethylsilylacetylene took place smoothly to afford expected
coupling products in up to 80% isolated yields.9 These results will
be published in a forthcoming paper, together with the data for the
RCM of the coupling product.
13 Crystal data for anti,E,E-6a: C28H44Br2Si2, Mr: 596.63, colorless
prism, 0:20 ꢃ 0:20 ꢃ 0:10 mm3, monoclinic, space group P21=c,
ꢁ
Figure 1. ORTEP drawings of anti,E,E-6a determined by
X-ray crystallography. (a) side view; (b) top view. Selected bond
lengths (A) and dihedral angles ( ): C8–C9 1.335(16), Si1–C1
1.900(2), C2–Br1 1.913(2), C7–C8–C9–C10 178.1(5); C14–
Si1–C1–C2 179.5(2).
˚
a ¼ 9:084ð1Þ, b ¼ 16:127ð1Þ, c ¼ 9:967ð1Þ A, ꢂ ¼ 101:627ð2Þ ,
3
V ¼ 1430:3ð2Þ A , Z ¼ 2, Dcalc ¼ 1:385 g cmꢂ3
,
Mo Kꢃ (ꢄ ¼
˚
ꢁ
˚
˚
0:7107 A), T ¼ 223 K, 3277 unique reflections were collected,
2593 observed [I > 2ꢅðIÞ]. Final Goof ¼ 1:04, R1 ¼ 0:0358
[I > 2ꢅðIÞ], 164 parameter. Crystallographic data of anti,E,E
isomers of 6a, 6b, and 6d, syn,E,E-6b, anti-7c, and 9d have been
deposited with Cambridge Crystallographic Data Centre as supple-
mentary publication no. CCDC-646084, CCDC-646083, CCDC-
646082, CCDC-654124, CCDC-654125, and CCDC-65426, re-
spectively.9
This work was supported by the Ministry of Education,
Culture, Sports, Science and Technology of Japan [Grant-in-
Aid for Scientific Research on Specially Promoted Research
(No. 17002005)].