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5.02 (1H, dd, J¼10, 2 Hz, CHvCH2), 4.22 (1H, dd, J¼8,
5 Hz, C(4)H), 4.13 (1H, d, J¼5 Hz, C(2)H), 2.74 (1H, dd,
J¼10, 4 Hz, C(6a)H), 2.63–2.53 (1H, m, allylic CH2),
2.42–.33 (2H, m, allylic CH2 and C(3)H), 2.00–1.90 (2H,
m, C(5)H exo, C(6)H exo), 1.89–1.80 (1H, m, C(6)H endo),
1.45–1.33 (1H, m, C(5)H endo), 0.91 (9H, s, CMe3), 0.90
(9H, s, CMe3), 0.18 (3H, s, SiMe), 0.16 (3H, s, SiMe), 0.12
(3H, s, SiMe), 0.07 (3H, s, SiMe); dC (100 MHz) 216.6
(CvO), 137.4 (CHvCH2), 116.3 (CHvCH2), 90.0 (COSi),
82.4 (CHOSi), 76.6 (CHOH), 55.8 (CHCO), 44.5 (homo-
allylic CH), 33.7 (CH2CHOSi), 28.3 (allylic CH2), 25.8
(CMe3), 25.8 (CMe3), 23.0 (CH2), 18.3 (CMe3), 17.9
(CMe3), 22.3 (SiMe), 22.4 (SiMe), 24.1 (SiMe), 24.8
(SiMe); m/z (CIþ) 458 (100%, M þNHþ4 ), (Found (ESþ)
MþNHþ4 458.3126, C23H48NO4Si2 requires 458.3122); data
for endo-3: Rf 0.39 (50% Et2O/petroleum ether); nmax(thin
film)/cm21 3480w, 2956s, 2938s, 1749s, 1362w, 1096s,
836s, 775s; dH (400 MHz, D2O in CDCl3) 6.09 (1H, dddd,
J¼17, 10, 8, 6 Hz, CHvCH2), 5.17 (1H, dm, J¼17 Hz,
CHvCH2), 5.06 (1H, dm, J¼8 Hz, CHvCH2), 4.37 (1H,
dd, J¼13, 3 Hz, C(2)H), 4.13 (1H, dd, J¼11, 6 Hz, C(4)H),
2.90–2.85 (1H, m, allylic CH2), 2.68–2.63 (1H, m,
C(6a)H), 2.47–2.35 (1H, m, allylic CH2), 2.09–1.80 (4H,
m, C(3)H, C(6)H exo and endo, C(5)H exo), 1.36–1.26 (1H,
m, C(H)5 endo), 0.94 (9H, s, CMe3), 0.91 (9H, s, CMe3),
0.14 (3H, s, SiMe), 0.12 (3H, s, SiMe), 0.10 (3H, s, SiMe),
0.08 (3H, s, SiMe); dC (100 MHz) 216.0 (CvO), 138.5
(CHvCH2), 115.4 (CHvCH2), 86.1 (COSi), 82.8
(CHOSi), 80.5 (CHOH), 54.1 (CHCO), 46.9 (homoallylic
CH), 35.1 (allylic CH2), 32.9 (CH2CHOSi), 25.8 (2£CMe3),
21.6 (CH2), 18.3 (CMe3), 17.9 (CMe3), 22.5 (SiMe), 22.6
(SiMe), 24.1 (SiMe), 24.8 (SiMe); m/z (CIþ) 458
(100%, MþNHþ4 ), (Found (ESþ) MþNHþ4 458.3127,
C23H48NO4Si2 requires 458.3122).
0.40 (50% Et2O/petroleum ether); nmax(thin film)/cm21
2956s, 2936s, 1704s, 1253m, 1098m, 836m, 775m; dH
(400 MHz) 5.71 (1H, ddt, J¼17, 10, 7 Hz, CHvCH2),
5.06 (1H, dm, J¼17 Hz, CHvCH2), 5.06–5.04 (1H, m,
CHvCH2), 5.02 (1H, br t, J¼6 Hz, C(4)H), 3.08–3.00
(1H, m, C(2)H), 2.85 (1H, dd, J¼19, 6 Hz, allylic CH2),
2.68–2.60 (1H, m, C(3)H), 2.50–2.40 (2H, m), 2.41 (1H,
dd, J¼19, 2 Hz, allylic CH2), 2.28–2.19 (1H, m), 2.15–2.05
(2H, m), 0.91 (9H, s, CMe3), 0.12 (3H, s, SiMe), 0.11 (3H, s,
SiMe); dC (100 MHz) 203.5 (CvO), 186.8 (CvCCHOSi),
148.9
(CvCCHOSi),
134.9
(CHvCH2),
117.4
(CHvCH2), 73.0 (CHOSi), 46.3, 38.9, 36.6, 34.7 (homo-
allylic CH), 25.7 (CMe3), 22.8, 18.0 (CMe3), 24.4 (SiMe),
24.9 (SiMe); m/z (CIþ) 161 (100%, M231), 293 (80,
MHþ); (Found (ESþ) MþHþ 293.1934, C17H29O2Si
requires 293.1937).
4.1.13. (2R,3R,4S)-3-Allyl-4-(tert-butyldimethylsilyloxy)-
3,4,5,6-tetrahydro-2-hydroxy-2H-pentalen-1-one 22 and
(2S,3R,4S)-3-allyl-4-(tert-butyldimethylsilyloxy)-3,4,5,6-
tetrahydro-2-hydroxy-2H-pentalen-1-one epi-22. KOH
(432 mg, 7.68 mmol) in dry MeOH (4 mL) was stirred
until dissolved, then the solution was cooled to 2158C and a
solution of 20 (150 mg, 0.51 mmol) in MeOH (2 mL) was
added. After 15 min, PhI(OAc)2 (249 mg, 0.78 mmol) was
added in one portion. The reaction mixture was stirred at
2158C for 1 h and then at 258C for 2 h and concentrated
under reduced pressure to give the crude a0-hydroxy-
dimethylacetals 21 [7:1 mixture as determined by 1H NMR
of C(2)H, for 21 dH (400 MHz) 4.40 (d, J¼7 Hz) and for
epi-21 dH 4.01 (d, J¼5 Hz)]. [In a separate experiment
column chromatography (8:2 petroleum ether/Et2O) gave
separable 21 and epi-21, as well as compounds 22. While 21
was stable enough to be characterised by NMR, epi-21 was
almost immediately hydrolysed in CDCl3. Data for 21: dH
(250 MHz, CDCl3 in D2O) 5.97–5.80 (1H, m, CHvCH2),
5.07 (1H, dm, J¼17 Hz, CHvCH2), 5.02–4.96 (1H, brd,
J¼10 Hz, CHvCH2), 4.89–485 (1H, m, C(4)H), 4.42 (1H,
d, J¼7 Hz, C(2)H), 3.40 (3H, s, OMe), 3.35 (3H, s, OMe),
2.86–2.76 (1H, m), 2.76–2.23 (4H, m), 2.05–1.87 (2H, m),
0.90 (9H, s, CMe3), 0.09 (3H, s, SiMe), 0.08 (3H, s,
SiMe); dC (63 MHz) 155.0 (CvC), 143.9 (CvC), 138.0
(CHvCH2), 115.4 (CHvCH2), 80.3 (CHO), 74.1 (CHO),
50.6 (OMe), 50.2 (OMe), 41.2 (homoallylic CH), 38.0, 33.8,
27.3, 25.8 (CMe3), 18.1 (CMe3), 24.3 (SiMe), 4.7 (SiMe)].
Crude 21 was dissolved in CH2Cl2 and treated with 10%
sulphuric acid at 258C for 10 min. After neutralisation with
saturated aq. NaHCO3 and extraction with ether, the
combined organic layers were dried and removed under
vacuum. Flash chromatography (7:3 petroleum ether/Et2O)
gave 22 (110 mg, 70%) and epi-22 (16 mg, 10%); data for
22: [a]2D5¼249.6 (c 1.0, CHCl3), Rf 0.24 (50% Et2O/
petroleum ether); nmax(thin film)/cm21 3424m, 2954s,
2930s, 1713s, 1638m, 1471m, 1255s, 837s, 776m; dH
(400 MHz) 5.75 (1H, ddt, J¼17, 10, 7 Hz, CHvCH2), 5.06
(1H, dm, J¼17 Hz, CHvCH2), 5.00 (1H, dm, J¼10 Hz,
CHvCH2), 4.96 (1H, m, C(4)H), 4.51 (1H, dd, J¼6, 3 Hz,
C(2)H), 3.28–3.21 (1H, m, C(3)H), 2.95 (1H, d, J¼3 Hz,
OH), 2.64–2.56 (1H, m), 2.54–2.42 (2H, m), 2.35–2.23
(2H, m), 2.11–2.02 (1H, m), 0.92 (9H, s, CMe3), 0.14
(3H, s, SiMe), 0.12 (3H, s, SiMe); dC (100 MHz) 204.0
(CvO), 184.0 (CvCCHOSi), 144.7 (CvCCHOSi), 136.1
(CHvCH2), 116.9 (CHvCH2), 78.9 (CHOH), 73.5
4.1.11. (4S)-4-(tert-Butyldimethylsilyloxy)-3,4,5,6-tetra-
hydro-2H-pentalen-1-one 19. DBU (117 mL, 0.78 mmol)
was added to a stirred solution of ketone 14 (150 mg,
0.39 mmol) in anhydrous MeCN (3.0 mL), and stirred at
258C for 2 days. The solvent was evaporated and the crude
mixture was subjected to flash chromatography (7:3
petroleum ether/Et2O) to give the enone 19 (88 mg, 90%)
as a colourless oil; Rf 0.19 (50% Et2O/petroleum ether);
n
max(thin film)/cm21 2954s, 2938s, 1705s, 1257m, 1096m,
838m, 775m; dH (200 MHz) 5.00–4.93 (1H, m, C(4)H),
2.77–2.60 (4H, m), 2.57–2.31 (2H, m), 2.30–2.08 (2H, m),
0.92 (9H, s, CMe3), 0.12 (3H, s, SiMe), 0.11 (3H, s, SiMe);
dC (50 MHz) 204.6 (CvO), 184.8 (CvCCHOSi), 148.9
(CvCCHOSi), 74.7 (CHOSi), 40.8, 38.9, 25.8 (CMe3),
23.3, 22.8, 18.3 (CMe3), 24.6 (SiMe), 24.8 (SiMe); m/z
(CIþ) 140 (100%), 123 (70), 270 (40), 253 (30); (Found
(ESþ) MþHþ 253.1622, C14H25O2Si requires 253.1624);
the ee (80%) was determined by chiral GC (100–1408C,
18C min21, 1 mL min21) tRmj, 116.0; tRmn, 121.4.
4.1.12. (3S,4S)-3-Allyl-4-(tert-butyldimethylsilyloxy)-
3,4,5,6-tetrahydro-2H-pentalen-1-one 20. DBU (152 mL,
1.02 mmol) was added to a stirred solution of ketone 17
(288 mg, 0.69 mmol) in anhydrous MeCN (3.0 mL), and
stirred at 258C for 2 days. The solvent was evaporated and
the crude mixture was subjected to flash chromatography
(8:2 petroleum ether/Et2O) to give the enone 20 (190 mg,
94%) as a colourless oil. [a]2D5¼235.3 (c 1.0, CHCl3); Rf