Organic Syntheses, Vol. 76, 199
Checked by Jing Zhang and Robert K. Boeckman, Jr..
1. Procedure
2. Notes
1. This procedure was reported by Hoff, Brandsma and Arens.
2
2.
Ethyl vinyl ether was purchased from Wako Pure Chemical Co., Ltd. or Aldrich Chemical Company, Inc. and freshly distilled.
4.
Propargyl alcohol was purchased from Nakalai Tesque, Inc. or Aldrich Chemical Company, Inc. and distilled.
5. This material has the following spectral properties:
1H NMR (500 MHz, CDCl
3) δ: 1.17 (t, 3 H, J = 7.1, CH
2Me), 1.29 (d, 3 H, J = 5.3, CHMe), 2.38 (t, 1 H, J = 2.6, H-1), 3.44-3.51 (m, 1 H, CH
2Me), 3.58-3.65 (m, 1 H, CH
2Me), 4.16 (d, 2 H, J = 2.6 H-3), 4.82 (q, 1 H, J = 5.3, OCHMe);
13C NMR (125 MHz, CDCl
3) δ: 15.3 (CH
2Me), 19.7 (CHMe), 52.5 (C-3), 60.8 (CH
2Me), 73.9 (C-1), 80.1 (C-2), 98.7 (OCHO). The checkers obtained material having bp
61-62°C/30 mm.
7. This material has the following spectral properties:
1H NMR (500 MHz, CDCl
3) δ: 1.20 (t, 3 H, J = 7.1, CH
2Me), 1.36 (d, 3 H, J = 5.1, CHMe), 3.46-3.52 (m, 1 H, CH
2Me), 3.72-3.79 (m, 1 H, CH
2Me), 4.92 (q, 1 H, J = 5.1, OCHMe), 5.34 (dd, 1 H, J = 6.0, 8.5, H-3), 5.37 (dd, 1 H, J = 6.0, 8.5, H-3), 6.68 (t, 1 H, J = 6.0, H-1);
13C NMR (125 MHz, CDCl
3) δ: 15.3 (CH
2Me), 20.4 (CHMe), 62.9 (CH
2Me), 89.2 (C-3), 99.9 (OCHO), 117.2 (C-1), 201.6 (C-2). The checkers obtained material having bp
55-56°C/35 mm.
8. This compound can be stored in the presence of a trace amount of radical inhibitor such as
4,4'-thiobis(2-tert-butyl-m-cresol) in a freezer for several months without significant decomposition. The checkers recommend that
1 be used as soon as practicable, as they observed significant amounts of polymerization upon storage for 1 month, even in the presence of the radical inhibitor. However, the checkers found that
2 is stable for 3 months in the presence of the inhibitor.
9. This procedure was reported by Reich, Kelly, Olson, and Holtan.
3
16. This material has the following spectral properties:
1H NMR (500 MHz, CDCl
3): δ 0.02 (s, 3 H, SiMe
2), 0.03 (s, 3 H, SiMe
2), 0.91 (s, 9 H, t-Bu), 1.16 (t, 3 H, J = 7.1, CH
2Me), 1.28 (d, 3 H, J = 5.1, CHMe), 3.38-3.45 (m, 1 H, CH
2Me), 3.68-3.74 (m, 1 H, CH
2Me), 4.92 (q, 1 H, J = 5.1, CHMe), 5.00 (d, 1 H, J = 8.5, H-3), 5.06 (d, 1 H, J = 8.5, H-3);
13C NMR (125 MHz, CDCl
3): δ −6.5 (SiMe
2), −6.6 (SiMe
2), 15.4 (CH
2Me), 17.5 (CMe
3), 20.5 (CHMe), 26.8 (CMe
3), 63.1 (CH
2Me), 84.4 (C-3), 100.1 (OCHO), 125.8 (C-1), 203.0 (C-2). The checkers obtained material having bp
108-109°C/8 mm.
20.
Methanol was purchased from Wako Pure Chemical Co., Ltd. or Aldrich Chemical Company, Inc. and used as received.
21. This material (E)-
3 has the following physical properties: R
f = 0.52 (hexane- Et
2O = 10:1). IR (neat) cm
−1: 1655, 1250;
1H NMR (500 MHz, CDCl
3) δ: 0.09 (s, 9 H, SiMe
3), 0.18 (6 H, SiMe
2), 0.87 (s, 9 H, t-Bu), 6.64 (d, 1 H, J = 19.2, H-2), 6.80 (d, 1 H, J = 19.2, H-3);
13C NMR (125 MHz, CDCl
3) δ: −5.8 (SiMe
2), −1.7 (SiMe
3), 16.7 (CMe
3), 26.7 (CMe
3), 145.1 (C-3), 147.1 (C-2), 236.3 (C-1). The checkers obtained material having bp
110-112°C/8 mm.
22. A mixture of
3 and its (Z)-isomer is obtained when
trifluoroacetic acid is used for the removal of the 1-ethoxyethyl protective group. A solution of crude
1-(tert-butyldimethylsilyl)-1-(1-ethoxyethoxy)-3-(trimethylsilyl)-1,2-propadiene obtained from
38.7 g (160 mmol) of 2 in 300 mL of THF-water (5:1) is cooled with an
ice-water bath, and
91 mL (135 g, 1.18 mol) of trifluoroacetic acid is added in one portion. The mixture is then placed in a refrigerator (ca. 4°C) and, after 12 hr, transferred to a
1-L separatory funnel containing 200 mL of water. The whole is extracted three times with
100-mL portions of pentane. The combined organic phases are washed thoroughly with aqueous saturated NaHCO
3 to remove
trifluoroacetic acid completely, and then with
100 mL of saturated brine. The
pentane solution is dried over MgSO
4, filtered, and concentrated at reduced pressure using a rotary evaporator. The residue is subjected to column chromatography (150-325 mesh
silica gel, 1 kg; elution with hexane-Et
2O, 40:1) to afford
9.89 g (
27%) of
(z.htm)-3 and
17.72 g (
46%) of
(e.htm)-3.
(z.htm)-3: bp
60°C/0.45 mm, an orange oil; IR (neat) cm
−1: 1655, 1245; R
f = 0.67 (hexane-Et
2O, 10:1);
1H NMR (500 MHz, CDCl
3) δ: 0.10 (s, 9 H, SiMe
3), 0.18 (6 H, SiMe
2), 0.91 (s, 9 H, t-Bu), 6.01 (d, 1 H, J = 14.1, H-2), 7.30 (d, 1 H, J = 14.1, H-3);
13C NMR (125 MHz, CDCl
3) δ: −7.0 (SiMe
2), −0.5 (SiMe
3), 17.0 (CMe
3), 26.7 (CMe
3), 144.6 (C-2), 144.9 (C-3), 238.0 (C-1).
25. The checkers found that recovery of pure material from the recrystallization is low (

30%) unless care is taken to use the minimum amount of total solvent and the minimum amount of ether. The checkers found use of pure hexanes more satisfactory in terms of recovery; however, the material obtained was pale yellow in color.
26. This material has the following physical properties : R
f = 0.47 (
hexane-
ethyl acetate (AcOEt) = 15:1); IR (KBr) cm
−1: 1705, 1645, 1250;
1H NMR (500 MHz, C
6D
6) δ: 0.08 (s, 9 H, SiMe
3), 0.21 (s, 3 H, SiMe
2), 0.26 (s, 3 H, SiMe
2), 1.00 (s, 9 H, t-Bu), 1.06 (dddd, 1 H, J = 3.9, 4.3, 13.0, 13.5, H-11), 1.21 (ddddd, 1 H, J = 4.7, 4.7, 13.5, 13.5, 13.5, H-9), 1.42-1.45 (m, 2 H, H-8), 1.52 (br d, 1 H, J = 13.5, H-10), 1.71 (br d, 1 H, J = 13.5, H-9), 1.79 (d, 1 H, J = 7.1, H-6), 2.05 (ddddd, 1 H, J = 3.9, 3.9, 13.5, 13.5, 13.5, H-10), 2.13 (br ddd, 1 H, J = 3.9, 3.9, 11.5, H-7), 2.27 (br d, 1 H, J = 13.0, H-11), 2.38 (br dd, 1 H, J = 3.9, 3.9, H-1), 2.85 (dd, 1 H, J = 1.9, 12.2, H-3), 3.67 (dd, 1 H, J = 1.9, 12.2, H-3), 5.00 (ddd, 1 H, J = 1.9, 1.9, 7.1, H-5);
13C NMR (125 MHz, C
6D
6) δ: −4.3, −4.2, −1.8, 18.2, 22.2, 25.8, 26.9, 27.6, 28.8, 31.3, 46.3, 51.3, 57.7, 106.0, 149.9, 203.3. Anal Calcd. for C
20H
38O
2Si
2: C, 65.51; H, 10.45, Found C, 65.26; H, 10.56. The structure was determined by X-ray crystallographic analysis.
5
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
The procedure described here illustrates an efficient preparation of cis-6-alkyl-5-trimethylsilyl-3-siloxy-3-cycloheptenones by reaction of
(E)-(β-(trimethylsilyl)acryloylsilane (
3) with the kinetic lithium enolate of an α,β-unsaturated methyl ketone generated with
lithium diisopropylamide in
tetrahydrofuran (Table).
5 This new [3 + 4] annulation
6 is also effective with 1-cyclopentenyl and 1-cyclohexenyl methyl ketones, affording all-cis bicyclic cycloheptenones in comparable yields as shown in the scheme. It is remarkable that reaction of
3 with 2'-bromoacetophenone enolate produces benzocycloheptenone, albeit in low yield, showing that a benzenoid unsaturation can also participate in the [3 + 4] annulation. In sharp contrast to the case of
(e.htm)-3, the reaction of
(z.htm)-3 under the same conditions is quite slow and affords only 5,6-trans isomer in much lower yield. The stereospecificity in the annulation has been rationalized by intermediacy of cis-1,2-divinylcyclopropanediolate (
6), which is generated from 1,2-adduct (
5) by way of a Brook rearrangement/cyclopropanation sequence in a concerted manner. Compound
6 is expected rapidly to undergo a stereospecific oxyanion-accelerated Cope rearrangement to
7. The low yields in the reaction of (Z)-
3 is attributed to slowness in the initial 1,2-addition step since substantial amount of the starting material is recovered.
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