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M. C. Maestro et al. / Tetrahedron: Asymmetry 10 (1999) 3593–3599
NMR: 170.7, 108.0, 98.8, 77.8, 70.1, 54.3, 47.4, 39.4, 34.0, 31.2, 25.4, 22.9, 22.1, 20.7, 15.4, 10.8. IR
(CHCl3): 1800, 1785, 1650. MS (15 eV) m/z (relative intensity): 312 (M++1, 9), 268 (2), 239 (6), 139
(100), 138 (24), 123 (3), 99 (36), 83 (65), 81 (18).
3.4. Reaction with malononitrile
3.4.1. (1S,4R,5R)-6,6-Dicyano-4-(l-menthyloxy)-3-oxabicyclo[3.1.0]hexan-2-one 4
The compound prepared according to the general procedure A was purified by column chromatography
(hexane:acetone, 9:1), yield 63% (Table 1, entry 4). Pure 4 (yield 70%) was also obtained following
the general procedure B by (hexane:acetone, 10:1) chromatographic separation (Table 1, entry 5). Mp
200–202°C; [α]D25 −194.7 (c 1, CHCl3). Anal. calcd for C17H22N2O3: C, 67.53; H, 7.33; N, 9.26. Found:
C, 67.26; H, 7.35; N, 9.08. 1H NMR: 5.73 (s, 1H), 3.68 (dt, 1H, J=10.9 and 4.7), 3.32, 3.24 (AB system,
2H, J=5.5), 2.2–0.7 (m, 18 H); 13C NMR: 165.3, 110.9, 97.8, 79.5, 47.5, 39.8, 36.1, 33.9, 31.8, 31.3,
25.4, 22.9, 20.7, 15.5, 9.2. MS m/z (relative intensity): 257 (M+−45, 1), 217 (11), 138 (43), 123 (40), 95
(67), 81 (100).
3.5. Reaction with diethyl malonate
Following the general procedure B at 25°C, a 42:51:7 mixture (1H NMR) of compounds 5, 6 and
unreacted diethyl malonate was obtained (Table 1, entry 8). The separation of the mixture was obtained by
column chromatography (hexane:acetone, 5:0.3) to afford compounds 5 (40%) and 6 (50%). Compound
6 was obtained as sole product at lower temperature (−18°C) with the same yield (50%) (Table 1, entry
7).
3.5.1. (1S,4R,5R)-6.6-Diethoxycarbonyl-4-(l-menthyloxy)-3-oxabicyclo[3.1.0]hexan-2-one 5
1H NMR: 5.61 (s, 1H), 4.22 (m, 4H), 3.52 (dt, 1H, J=10.2 and 4.3), 2.88 (s, 2H) 1.30 (t, 6H, J=7.2),
2.2–0.7 (m, 18H); 13C NMR: 166.6, 165.9, 98.2, 77.9, 62.9, 62.6, 47.6, 41.6, 40.0, 34.5, 34.1, 31.3, 29.7,
25.3, 23.0, 20.8, 15.5, 14.0, 13.8, 13.7. MS m/z (relative intensity): 323 (M+−73, 1), 241 (100), 213 (61),
185 (66), 167 (25), 139 (40), 138 (35), 123 (30), 95 (73), 81 (55).
3.5.2. (1S,4R,40R,5S,50R,6S)1-Bromo-4,50-di(l-menthyloxy)-2-oxo-40 -[bis(ethoxycarbonyl]methyl)-3-
oxabicyclo[3.1.0]hexane-6-spiro-tetrahydrofuran-2-one 6
25
Mp 57–59°C; [α]D −99.0 (c 1, CHCl3). Anal. calcd for C35H53O10Br: C, 58.90; H, 7.49; Br, 11.20.
Found: C, 59.17; H, 7.45; Br, 11.18. 1H NMR: 5.95 (s, 1H), 5.75 (s, 1H), 4.22 (m, 4H), 3.61, 3.52 (2dt,
2×1H, J=10.2 and 4.3), 3.35 (d, 1H, J=4.3), 3.05 (s, 1H), 2.72 (d, 1H, J=4.3), 1.30, 1.35 (t, 2×3H,
J=7.1), 2.3–0.7 (m, 18H); 13C NMR: 168.7, 167.4, 166.2, 166.0, 100.0, 95.9, 78.0, 76.0, 62.6, 62.2, 50.6,
47.1, 44.2, 39.6, 38.8, 38.5, 37.2, 34.2, 33.8, 33.7, 31.0, 25.2, 24.3, 22.9, 22.4, 21.8, 21.7, 20.6, 20.3,
15.3, 15.1, 13.6, 13.4. IR (CHCl3): 1780, 1740, 1720. MS m/z (relative intensity): 712–714 (M++1, 0.2),
557–559 (7), 249 (7), 161 (25), 139 (58), 138 (49), 123 (30), 95 (91), 83 (100), 81 (84).
3.6. Reaction with ethyl acetoacetate
3.6.1. (3aR,4R,6aS)-3-Ethoxycarbonyl-4-(l-menthyloxy)-2-methyl-3a,6a-dihydrofuro[3,4-b]furan-
6(4H)-one 8
The compound was obtained as a sole diastereoisomer following procedures A (yield 60%), B (yield
50%) or C (yield 75%) (Table 2, entries 4–6). Purification was effected by column chromatography on