P. J. Coelho, L. Blanco / Tetrahedron 59 (2003) 2451–2456
2455
7.5–7.6 (m, 2H). 13C NMR: 25.8 (SiCH3), 55.8 (CH2O),
119.4, 127.5, 128.0, 128.4, 129.7, 130.4, 134.3, 134.5,
139.3, 148.4, 166.9 (CvO). MS: m/z (%) 258 (0.9, Mþ),
243 (23), 205 (67), 181 (40), 173 (39), 145 (31), 137 (25),
128 (100), 121 (97), 105 (44), 95 (26), 91 (20), 55 (81), 53
(20), 43 (34).
23.9, 38.9, 60.3, 123.6, 126.1, 128.4, 130.5, 133.4, 134.5,
175.6 (CvO). MS: m/z (%) 259 (15.1), 258 (67, Mþ), 257
(10), 243 (5), 151 (29), 149 (26), 137 (47), 136 (36), 135
(72), 134 (69), 133 (35), 123 (50), 122 (21), 121 (100), 120
(44), 105 (87), 107 (30), 106 (26), 93 (25), 92 (23), 91 (60),
80 (61), 79 (96), 77 (55), 53 (33), 43 (38).
4.5.2. (E)-2-Cyclohexyl-2-methyl-2-silahexa-3,5-dien-1-
yl acrylate (5b). Yield: 40%. IR: 1740 (CvO), 1535,
1260 (SiCH3). H NMR: 0.13 (s, 3H, SiCH3), 0.7–1.0 (m,
4.6.2. 4-Cyclohexyl-4-methyl-4-sila-4a,7,8,8a-tetra-
hydroisochromanon-1-one (6b). Yield: 68%. IR: 1735
(CvO), 1650, 1255 (SiCH3). 1H NMR: 0.05, 0.10, 0.17 (s,
3H, SiCH3), 0.8–1.0 (m, 1H), 1.1–1.4 (m, 5H), 1.6–1.9 (m,
6H), 2.0–2.3 (m, 3H), 2.3–2.5 (m, 1H), 3.00 (ddd, J¼3, 7,
7 Hz, 1H), 3.90 (d, J¼14.7 Hz) and 4.19 (d, J¼14.7 Hz)
[AB system, minor isomer] and 4.00 (d, J¼15.0 Hz) and
4.09 (d, J¼15.0 Hz) [AB system, major isomer] (2H), 5.45–
5.75 (m, 2H). 13C NMR: 210.4, 29.0, 26.6, 20.3, 22.3,
22.4, 22.5, 22.9, 23.7, 23.8, 24.1, 24.3, 26.5, 26.6, 26.9,
26.98, 27.02, 27.4, 27.5, 27.7, 28.0, 38.8, 38.9, 39.4, 59.0,
59.2, 59.4, 123.8, 124.6, 125.3, 125.4, 126.4, 176.0 (CvO).
MS: m/z (%) 266 (3.9), 265 (9.7), 264 (14.9, Mþ), 181 (11),
137 (14), 99 (20), 81 (25), 80 (100), 79 (45), 77 (27), 75
(63), 61 (31), 59 (72), 58 (21), 55 (24), 45 (28), 43 (33).
1
1H), 1.1–1.35 (m, 5H), 1.6–1.8 (m, 5H), 3.97 (s, 2H), 5.18
(d, J¼9.8 Hz, 1H), 5.27 (d, J¼18.4 Hz, 1H), 5.81 (dd,
J¼10.3, 1.5 Hz, 1H), 5.81 (d, J¼18.7 Hz, 1H), 6.14 (dd,
J¼10.3, 17.5 Hz, 1H), 6.25–6.45 (m, 2H), 6.60 (dd,
J¼10.3, 18.6 Hz, 1H). 13C NMR: 28.3 (SiCH3), 23.8,
26.7, 27.2, 27.3, 27.9, 54.8 (CH2O), 118.5, 128.0, 128.5,
130.2, 139.5, 147.3, 167.0 (CvO). MS: m/z (%) 250 (0.5),
249 (1.4), 211 (4.7), 181 (100), 109 (38), 97 (27), 95 (19), 55
(52).
4.5.3. (E)-2-(2-Methoxyphenyl)-2-methyl-2-silahexa-3,5-
dien-1-yl acrylate (5c). Acryloyl chloride (0.200 mL,
2.4 mmol) was added dropwise to a stirred solution of
hydroxymethylsilane 4c (190 mg, 0.812 mmol) and N,N-
dimethylaniline (0.200 mL) in CH2C12 (25 mL) at 08C
under argon atmosphere. After stirring for 30 min at room
temperature the solution was quenched with HCl 1 M
(10 mL) and the resulting mixture was extracted with
CH2C12. The combined organic extracts were dried over
anhydrous Na2SO4, concentrated and the product was
purified by column chromatography (n-hexane/ether
80/20) to give 223 mg of acrylate 5c (95% yield). IR:
4.6.3. 4-Methoxyphenyl-4-methyl-4-sila-4a,7,8,8a-tetra-
hydroisochromanon-1-one (6c). Yield: 74%. 1H NMR:
0.34, 0.40, 0.47 and 0.54 (4 s, 3H, SiCH3), 1.7–1.9 (m, 1H),
2.0–2.3 (m, 2H), 2.4–2.6 (m, 2H), 3.12 (ddd, J¼4, 7, 6 Hz,
1H), 4.82 (s, 3H), 5.23 (d, J¼14.7 Hz) and 5.42 (d,
J¼14.7 Hz) [AB system, 2H], 5.6–5.8 (m, 2H), 6.90 (d,
J¼7.5 Hz, 1H), 7.02 (t, J¼7.5 Hz, 1H), 7.3–7.5 (m, 2H).
13C NMR: 27.0 (SiCH3), 21.0, 22.3, 24.0, 38.5, 55.2, 60.1,
109.7, 120.9, 121.8, 124.5, 125.6, 132.3, 135.1, 164.1, 176.1
(CvO). MS: m/z (%) 289 (11), 288 (33, Mþ), 287 (7), 273
(2), 149 (100), 135 (29), 119 (31), 105 (41), 79 (48), 77 (23),
59 (28).
1
1730 (CvO), 1590, 1240 (SiCH3). H NMR: 0.47 (s, 3H),
3.82 (s, 3H), 4.22 (s, 2H), 5.15–5.30 (m, 2H), 5.77 (dd,
J¼1.9, 10.2 Hz, 1H), 6.05 (d, J¼18.4 Hz, 1H), 6.11 (dd,
J¼10.2, 17.2 Hz, 1H), 6.3–6.5 (m, 2H), 6.67 (dd, J¼10.1,
18.4 Hz, 1H), 6.85 (d, J¼8.5 Hz, 1H), 6.98 (t, J¼7.2 Hz,
1H), 7.35–7.45 (m, 2H). 13C NMR: 26.0 (SiCH3), 55.0,
56.1, 109.5, 118.5, 120.6, 122.6, 126.5, 128.6, 130.0, 131.6,
135.8, 139.6, 147.3, 164.2, 167.0 (CvO). MS: m/z (%) 289
(0.6), 288 (1.3, Mþ), 273 (29), 236 (24), 235 (86), 203 (21),
181 (40), 173 (40), 151 (31), 145 (32), 128 (100), 121 (84),
105 (36), 91 (33), 77 (30), 75 (72), 59 (41), 55 (67).
Acknowledgements
We thank the Portuguese Junta Nacional para a Investigac¸a˜o
´ ´
Cientıfica e Tecnologica (JNICT) for awarding a PhD grant
to P. J. Coelho.
4.6. Lewis acid intramolecular Diels–Alder catalysed
reaction: general procedure
References
A 1 M EtAlCl2 solution in CH2Cl2 (4.0 mL, 4.0 mmol) was
added to a solution of silatriene 5a–c (1.0 mmol) in CH2Cl2
(20 mL) under argon. After complete consumption of the
silatriene (TLC), the reaction mixture was quenched with
saturated aqueous NH4Cl and the resulting mixture was
extracted with CH2Cl2. The combined organic extracts were
dried over anhydrous Na2SO4, concentrated, and the crude
silaisochromanone 6 was purified by silica gel column
chromatography (n-hexane/Et2O).
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1
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