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M. Wenz et al.
PAPER
High Pressure Diels–Alder Reactions; General Procedure
Equimolar amounts of the starting materials were converted in
CH2Cl2 in a sealed teflon tube. The mixture was kept under a pres-
sure of 10 kbar for 3 days at r.t. All volatile materials were removed
and the oily residue was chromatographed.
1H, J = 1.5/13 Hz, H-9b), 3.13 (s, 3H, H-18), 3.18 (s, 3H, H-21),
3.62 (tm, 1H, J = 5 Hz, H-13), 3.81–3.85 (m, 1H, H-7), 4.19 (dm,
1H, J = 7.5 Hz, H-3), 4.35 (d, 1H, J = 13 Hz, H-9a), 4.37 (d, 1H, J
= 7 Hz, H-20), 4.66 (d, 1H, J = 7 Hz, H-20), 5.67 (dddd, 1H, J = 2.5/
2.5/2.5/10.5, H-5), 5.81 (dddd, 1H, J = 1.5/1.5/1.5/10 Hz, H-6),
10.12 (s, 1H, H-19).
13C NMR (100 MHz, C6H6): d = 26.42 (CH2, C-4), 27.1 (CH2, C-
14), 27.4 (CH2, C-12), 29.5 (CH3, C-16), 33.3 (CH3, C-17), 33.7
(Cq, C-15), 39.3 (CH2, C-9), 43.2 (CH, C-3), 54.0 (CH, C-1), 54.9
(CH3, C-21), 55.3 (CH3, C-18), 58.1 (Cq, C-8), 58.2 (CH, C-11),
67.1 (CH, C-13), 80.0 (CH, C-7), 94.0 (CH2, C-20), 125.3 (CH, C-
6), 128.0 (CH, C-5), 200.0 (CH, C-19), 212.6, 214.9 (Cq, C-2, C-
10).
rac-Spiro[(1,3)-dioxolane-2,13-(3-cis)-7b-methoxy-2,10,19-oxo-
4,12-dinortaxane] (4a) and rac-Spiro[(1,3)-dioxolane-2,13-(3-
cis)-7a-methoxy-2,10,19a-oxo-4,12-dinortaxane] (4b)
Conversion of dienophile 12 (14 mg, 0.048 mmol) with (E)-1-meth-
oxybuta-1,3-diene (40 mg, 0.48 mmol) yielded 4a and 4b as parts
of a 1:1 diastereomeric mixture. Separation by chromatography on
silica gel (hexane/MTBE, 2:1) yielded 4a (5 mg, 28%) and 4b (5
mg, 28%) as colorless oils.
HRMS: (C21H30O6) calcd 378.2042, found 378.2042.
IR: n = 1727, 1690 cm–1.
4a
1H NMR (400 MHz, C6H6): d = 0.84 (s, 3H, H-17), 1.29 (s, 3H, H-
16), 1.54 (ddd, J = 1.5/1.5/6.5 Hz, 1H, H-1), 1.83 (dm, 1H, J = 16
Hz, H-12), 1.93 (dd, J = 6.5/15 Hz, 1H, H-14), 2.02 (dm, 1H, J = 19
Hz, H-4a), 2.18 (dd, 1H, J = 8/16 Hz, H-12), 2.33 (dm, 1H, J = 8
Hz, H-11), 2.49 (dm, 1H, J = 19 Hz, H-4b), 3.07 (dd, 1H, J = 1.5/
14 Hz, H-9a), 3.09 (ddd, 1H, J = 2/2/15 Hz, H-14), 3.14 (s, 3H, H-
18), 3.35–3.50 (m, 4H, H-20, H-21), 3.96–3.98 (m, 1H, H-7), 4.16
(d, 1H, J = 7.5 Hz, H-3), 4.17 (d, 1H, J = 14 Hz, H-9b), 5.67 (dddd,
1H, J = 2.5/2.5/2.5/10.5 Hz, H-5), 5.83 (dm, 1H, J = 10.5 Hz, H-6),
10.13 (s, 1H, H-19).
5b
1H NMR (400 MHz, C6H6): d = 0.64 (s, 3H, H-17), 1.27 (s, 3H, H-
16), 1.69 (dt, 1H, J = 7/17 Hz, H-12ax), 1.77 (dt, 1H, J = 7/17 Hz, H-
14ax), 1.88 (dm, 1H, J = 19 Hz, H-4a), 1.88 (dm, 1H, J = 7 Hz, H-
1), 1.93 (dm, 1H, J = 17 Hz, H-14eq), 2.07 (dm, 1H, J = 7 Hz, H-11),
2.08 (dm, 1H, J = 17 Hz, H-12eq), 2.18 (dm, 1H, J = 19 Hz, H-4b),
2.81 (dm, 1H, J = 11.5 Hz, H-9b), 3.31 (s, 3H, H-21), 3.38 (s, 3H,
H-18), 3.71 (t, 1H, J = 7.5 Hz, H-13), 3.93 (d, 1H, J = 11.5 Hz, H-
9a), 3.98–4.02 (m, 1H, H-7), 4.66 (d, 1H, J = 7 Hz, H-20), 4.73 (d,
1H, J = 7 Hz, H-20), 4.95 (d, 1H, J = 6.5 Hz, H-3), 5.67 (dm, 1H, J
= 10 Hz, H-5), 5.96 (dm, 1H, J = 10 Hz, H-6), 10.00 (d, 1H, H-19).
13C NMR (100 MHz, C6H6): d = 26.1 (CH2, C-4), 28.5 (CH3, C-16),
32.4 (Cq, C-15), 32.6 (CH2, C-12), 33.1 (CH2, C-14), 33.5 (CH3, C-
17), 39.0 (CH2, C-9), 42.8 (CH, C-3), 53.8 (Cq, C-8), 56.5 (CH, C-
1), 57.6 (CH3, C-18), 58.7 (CH, C-11), 62.8 (CH2, C-20), 63.5 (CH2,
C-21), 79.4 (CH, C-7), 106.1 (Cq, C-13), 124.9 (CH, C-6), 127.5
(CH, C-5), 199.4 (CH, C-19), 211.6, 213.6 (Cq, C-2, C-10).
13C NMR (100 MHz, C6H6): d = 27.7 (CH2, C-14), 27.9 (CH2, C-
12), 28.0 (CH2, C-4), 28.8 (CH3, C-16), 31.2 (CH3, C-17), 36.3 (Cq,
C-15), 39.0 (CH2, C-9), 42.3 (CH, C-3), 54.8 (Cq, C-8), 55.6 (CH3,
C-), 56.4 (21CH, C-1), 57.1 (CH, C-11), 57.1 (CH3, C-18), 66.3
(CH, C-13), 75.8 (CH, C-7), 94.7 (CH2, C-20), 126.7 (CH, C-6),
127.6 (CH, C-5), 200.2 (CH, C-19), 211.2, 216.0 (Cq, C-2, C-10).
HRMS: (C21H28O6) calcd 376.1886, found 376.1886.
IR: n = 1727, 1692 cm–1.
HRMS: (C21H30O6) calcd 378.2042, found 378.2042.
IR: n = 1723, 1686 cm–1.
4b
1H NMR (400 MHz, C6H6): d = 0.88 (s, 3H, H-17), 1.26 (s, 3H, H-
16), 1.89 (dm, 1H, J = 19 Hz, H-4b), 2.00–2.20 (m, 6H, H-1, H-11,
H12ax,eq, H14ax,eq), 2.23 (dm, 1H, J = 19 Hz, H-4a), 2.38 (d, 1H, J =
11.5 Hz, H-9b), 3.34–3.41 (m, 2H, H-20,20’), 3.41 (s, 3H, H-18),
3.62–3.75 (m, 2H, H-21,21’), 3.89 (d, 1H, J = 11.5 Hz, H-9a), 3.95–
3.99 (m, 1H, H-7b), 4.77 (d, 1H, J = 6.5 Hz, H-3b), 5.67 (dm, 1H,
J = 10 Hz, H-5), 5.97 (dm, 1H, J = 10 Hz, H-6), 10.03 (s, 1H, H-19).
(1R,5S)-2,8,8-Trimethylbicyclo[3.2.1]oct-2-en-7-one (7) and
(1S,5S)-2,2,4-Trimethylbicyclo[3.2.1]oct-3-en-6-one (8)
(1S)-(–)-b-pinene (0.500 mol, 79.3 mL) was degased with Ar for 10
min, then iron pentacarbonyl (0.100 mol, 13.9 mL) was added and
the mixture was stirred at 175 °C/2 bar(CO) for 5 days. The crude
product, containing elementary iron, was distilled using a vigreux
column to yield (1S)-(–)-a-pinene (8.58 g, 13%) and the 1:1 mixture
of 7 and 8 (63.0 g, 77%) as a colourless oil; bp 56 °C (0.1 mm). Sep-
aration was carried out as published.6
13C NMR (100 MHz, C6H6): d = 27.9 (CH3, C-16), 28.3 (CH2, C-4),
31.1 (CH3, C-17), 33.7, 33.8 (CH2, C-12, C-14), 36.8 (Cq, C-15),
38.6 (CH2, C-9), 42.9 (CH, C-3), 54.7 (Cq, C-8), 57.1 (CH3, C-18),
57.9, 58.0 (CH, C-1, C-11), 62.9 (CH2, C-20), 64.2 (CH2, C-21),
75.3 (CH, C-7), 105.3 (Cq, C-13), 126.8 (CH, C-6), 128.0 (CH, C-
5), 200.0 (CH, C-19), 210.9, 215.3 (Cq, C-2, C-10).
7
[a]D20: +674 (c = 6.7, CDCl3).
1H NMR (400 MHz, CDCl3): d = 0.97 (s, 3H, C8-CH3),, 1.00 (s, 3H,
C8-CH3), 1.70 (br s, 3H, C4-CH3), 1.89 (m, 1H, C1-H), 1.92 (dm,
1H, J = 18 Hz, C2-Ha), 2.03 (d, 1H, J = 18.5 Hz, C7-Ha), 2.25 (s, 1H,
C5-H), 2,46 (dm, 1H, J = 18Hz, C2-Hb), 2.56 (dd, 1H, 18.5/7.5 Hz,
C7-Hb), 5.41 (sbr, 1H, C3-H); (assignment by C/H-COSY).
13C NMR (50 MHz, CDCl3): d = 19.7 (CH3, C8-CH3), 26.6 (CH3,
C8-CH3), 22.4 (CH3, C4-CH3), 32.4 (CH2, C2), 37.3 (Cq, C8), 38.6
(CH, C1), 42.8 (CH2, C7), 63.4 (CH, C5), 121.0 (CH, C3), 131.5 (Cq,
C4), 210.9 (Cq, C6); (assignment by C/H-COSY).
HRMS: (C21H28O6) calcd 376.1886, found 376.1886.
IR: n = 1725, 1688 cm–1.
rac-(3-cis)-7b-Methoxy-13a-methoxymethoxy-2,10,19-trioxo-
4,12-dinortaxane (5a) and rac-(3-cis)-7a-Methoxy-13a-meth-
oxymethoxy-2,10,19a-trioxo-4,12-dinortaxane (5b)
Reaction of dienophile 2 (19 mg, 0.05 mmol) with (E)-1-meth-
oxybuta-1,3-diene (42 mg, 0.50 mmol) yielded 5a and 5b as a 2:1
diastereomeric mixture. Separation by chromatography on silica gel
(hexane/MTBE, 2:1) yielded 5a (10 mg, 53%) and 5b (5 mg, 26%)
as colourless oils.
HRMS: (C11H16O) calcd 164.1201,
found 164.1201.
IR: n = 1743 cm–1.
5a
8
1H NMR (400 MHz, C6H6): d = 0.66 (s, 3H, H-17), 1.31 (s, 3H, H-
16), 1.41 (ddd, 1H, J = 1/1/6.5 Hz, H-1), 1.59 (ddd, 1H, J = 6.5/6.5/
15.5 Hz, H-14eq), 1.67–1.72 (m, 2H, H-12ax,eq), 2.02 (dddd, 1H, J =
2.5/2.5/2.5/19 Hz, H-4a), 2.22 (dm, 1H, J = 6 Hz, H-11), 2.48 (dm,
1H, J = 19 Hz, H-4b), 2.95 (dm, 1H, J = 15.5 Hz, H-14ax), 3.02 (dd,
[a]D20: –635 (c = 3.3, CDCl3).
1H NMR (400 MHz, CDCl3): d = 0.88 (s, 3H), 1.02 (s, 3H), 1.68 (br
s, 3H), 1.86 (ddt, 1H, J = 4.5/4.5/11.5 Hz), 2.08 (dd, 1H, J = 3.5/11.5
Hz), 2.11–2.21 (m, 2H), 2.42–2.50 (m, 2H), 5.12 (br s, 1H).
Synthesis 1999, No. 4, 607–614 ISSN 0039-7881 © Thieme Stuttgart · New York