3-[(2-Furanyl)-hydroxymethyl]-3-buten-2-one (19).

Methyl vinyl ketone (7.01 g, 0.1 mol), 2-furaldehyde (9.6 g, 0.1 mol), and DABCO (1.68 g, 15 mmol) were dissolved in anhydrous THF (25 ml) and left at room temperature. After 24 h the solution was diluted with ether (100 ml), washed with 1 M HCl (3 x 30 ml) then with aqueous NaHCO3 (3 x 30 ml), and dried over MgSO4. Evaporation of the solvent furnished practically pure product (15.8 g, 95 %) which was further purified (with addition of 0.1 % of benzophenone) by bulb-to-bulb distillation (temperature 80 - 90 °C, 3.10-2 mm Hg) to give a slightly yellow oil 19[138] (14.8 g, 89 %). Freshly distilled product was dissolved in benzene (1 M solution) and stored at - 18 °C.

B.p. 80-90 °C, 3.10-2 mm Hg. IR (film, KBr): 3420s, 3147w, 3121w, 3002w, 2925w, 1675s, 1627m, 1501m, 1467w, 1428m, 1368s, 1325m, 1281m, 1226m, 1210m, 1180m, 1147s, 1125m, 1074m, 1039s, 1013s, 976s, 907w, 884m, 805m, 745s, 971w, 600m, 581m, 532w, 445w. 1H-NMR (400 MHz, CDCl3, 298 K): 7.34 (dd, 3J(35,34) = 1.8, 4J(35,33) = 0.9, 1H, HC(35)); 6.31 (ddd, 3J(34,33) = 3.3, 3J(34,35) = 1.8, 5J(34,31) = 0.3, 1H, HC(34)); 6.23 (d, 4J(4A,31) = 0.4, 1H, HAC(4)); 6.22 (ddd, 3J(33,34) = 3.3, 4J(33,35) Å 4J(33,31) Å 0.8, 1H, HC(33)); 6.09 (d, 4J(4B,31) = 1.2, 1H, HBC(4)); 5.61 (br. s, 1H, HC(31)); 3.33 (br. s, 1H, HO); 2.36 (s, 3H, H3C(1)). 13C-NMR (100 MHz, CDCl3, 298 K): 199.8 (C(2)); 154.3 (C(32)); 147.3 (C(3)); 142.1 (C(35)); 127.1 (C(4)); 110.4 (C(34)); 107.1 (C(33)); 67.0 (C(31)); 26.3 (C(1)). EI-MS: 166 (10, [M]+), 149 (32), 124 (31), 105 (7), 98 (10), 97 (37), 95 (24), 83 (8), 78 (11), 77 (14), 70 (12), 69 (16), 68 (10), 67 (9), 65 (7), 58 (11), 55 (19), 53 (7), 51 (10), 43 (100), 41 (15), 39 (18). DCI-MS: 185 (5, [M + 19]+), 184 (26, [M + 18]+), 167 (14), 166 (100), 158 (4), 150 (9), 149 (86), 141 (7), 124 (4), 95 (4), 55 (4), 43 (5), 39 (5), 35 (6). Anal. calc. for C9H10O3 (166.17): C 65.05, H 6.07; found: C 64.89, H 6.24.

Ethyl 3-acetyl-2-hydroxy-3-butenoate (20).

Methyl vinyl ketone (7.01 g, 0.1 mol), ethyl glyoxylate (50 % solution in toluene, 20.40 g, 0.1 mol), and DABCO (1.68 g, 15 mmol) were dissolved in anhydrous THF (25 ml) and left at room temperature. After 3 h the solution was diluted with ether (100 ml), washed with 1 M HCl (3 x 30 ml). Then the aqueous phase was extracted continuously overnight with ether (100 ml), and combined organic phases were dried over MgSO4. Evaporation of solvent furnished practically pure product (14.3 g, 83 %) which was further purified by bulb-to-bulb distillation (temperature 90 - 100 °C, 3.10-2 mm Hg) gave a slightly yellow oil 20[139] (12.7 g, 74 %).

B.p. 90-100 °C, 3.10-2 mm Hg. IR (film, KBr): 3457m, 2984m, 2939m, 1740s, 1681s, 1633w, 1467w, 1447m, 1370s, 1216s, 1140m, 1088s, 1025m, 978m, 914w, 864w, 586w, 478w. 1H-NMR (400 MHz, CDCl3, 298 K): 6.21 (s, 1H, HAC(4)); 6.12 (d, 4J(4B,2) = 0.7, 1H, HBC(4)); 4.81 (s, 1H, HC(2)); 4.22 (2q from AB x q, 3J(11,12) = 7.1, H2C(11)); 3.43 (br. s, 1H, HO); 2.36 (s, 3H, H3C(32)); 1.23 (t, 3J(12,11) = 7.1, 3H, H3C(12)). 13C-NMR (100 MHz, CDCl3, 298 K): 199.0 (C(31)); 173.1 (C(1)); 146.7 (C(3)); 129.2 (C(4)); 71.5 (C(2)); 62.6 (C(11)); 26.5 (C(32)); 14 (C(12)). EI-MS: 173 (12, [M + 1]+), 127 (11), 126 (20), 100 (10), 99 (100), 98 (11), 85 (66), 84 (5), 83 (13), 70 (19), 56 (7), 55 (17), 44 (95), 43 (7), 42 (5), 40 (16). Anal. calc. for C8H12O4 (172.18): C 55.81, H 7.02; found: C 55.61, H 6.86.

Ethyl 2-[(2-furanyl)-hydroxymethyl]-propenoate (21).

Ethyl propenoate (10.12 g, 0.1 mol), 2-furaldehyde (9.6 g, 0.1 mol), and DABCO (1.68 g, 15 mmol) were dissolved in anhydrous THF (25 ml) and left at room temperature. After 7 days the solution was diluted with ether (100 ml), washed with 1 M HCl (3 x 30 ml) then with aqueous NaHCO3 (3 x 30 ml), and dried over MgSO4. Evaporation of solvent furnished practically pure product (15.9 g, 81 %) which was further purified (with addition of 0.1 % of benzophenone) by bulb-to-bulb distillation (temperature 80 - 90 °C, 4.10-2 mm Hg) to give a colourless oil 21 (14.9 g, 76 %).

B.p. 80-90 °C, 4.10-2 mm Hg. IR (film, KBr): 3447s, 3148m, 3121m, 2985s, 2939m, 2907m, 2876m, 2664w, 1717s, 1633m, 1569w, 1501m, 1466m, 1447m, 1396m, 1371s, 1329s, 1283s, 1226m, 1176s, 1152s, 1114m, 1096m, 1075m, 1039s, 1013s, 959m, 930m, 883m, 864w, 820m, 798m, 742m, 700w, 600m, 540w, 503w. 1H-NMR (400 MHz, CDCl3, 298 K): 7.32 (dd, 3J(25,24) = 1.8, 4J(25,23) = 0.8, 1H, HC(25)); 6.33 (dd, 2J(3A,3B) Å 4J(3A,21) Å 0.9, 1H, HAC(3)); 6.27 (dd, 3J(24,23) = 3.2, 3J(24,25) = 1.8, 1H, HC(24)); 6.19 (ddd, 3J(23,24) = 3.3, 4J(23,25) Å 4J(23,21) Å 0.7, 1H, HC(23)); 5.91 (dd, 2J(3B,3A) Å 4J(3B,21) Å 1.1, 1H, HBC(3)); 5.54 (br. d, 3J(21,OH) Å 4.7, 1H, HC(21)); 4.16 (dq, 2J(11A,11B) = 10.8, 3J(11,12) = 7.2, 1H, HAC(11)); 4.13 (dq, 2J(11B,11A) = 10.8, 3J(11B,12) = 7.1, 1H, HBC(11)); 3.57 (br. d, 3J(OH,21) Å 5.7, 1H, HO); 1.21 (t, 3J(12,11) = 7.1, 3H, H3C(12)). 13C-NMR (100 MHz, CDCl3, 298 K): 166. 6 (C(1)); 154.9 (C(22)); 142.8 (C(25)); 140.4 (C(2)); 126.8 (C(3)); 110.9 (C(24)); 107.6 (C(23)); 67.5 (C(21)); 61.5 (C(11)); 14.5 (C(12)). EI-MS: 196 (17, [M]+), 179 (59), 167 (15), 151 (24), 150 (23), 149 (30), 123 (13), 122 (49), 106 (14), 99 (16), 97 (53), 95 (100), 94 (18), 81 (22), 78 (15), 77 (19), 69 (17), 68 (23), 66 (20), 55 (22). Anal. calc. for C10H12O4 (196.20): C 61.22, H 6.16; found: C 61.02, H 6.02.

3-[(2-Furanyl)-acetoxymethyl]-3-buten-2-one (22).

To a solution of 3-[(2-furanyl)-hydroxymethyl]-3-buten-2-one (10 ml of 1 M solution in benzene, 10 mmol) in dry methylene dichloride (50 ml) was added pyridine (0.89 ml, 11 mmol) and acetyl chloride (0.78 ml, 11 mmol) at 0° C. Then the mixture was stirred for 1h, and then treated with 3.7 % HCl (50 ml) and the aqueous phase extracted with methylene dichloride (2 x 20 ml). The combined organic phases were dried over Na2SO4. Evaporation of solvent furnished practically pure product (1.91 g, 92 %) which was further purified by bulb-to-bulb distillation (temperature 90 - 100 °C, 3.10-2 mm Hg) to give a colourless oil 22 (1.73 g, 83 %).

B.p. 90-100 °C, 3.10-2 mm Hg. IR (film, KBr): 3124w, 3004w, 1747s, 1681s, 1628s, 1547w, 1501m, 1471m, 1432m, 1392m, 1370s, 1271s, 1229s, 1178m, 1149m, 1123m, 1074w, 1018s, 976s, 923m, 884m, 823w, 806m, 751m, 643w, 600m, 570w, 492w, 483w. 1H-NMR (400 MHz, CDCl3, 298 K): 7.35 (dd, 3J(35,34) = 1.8, 4J(35,33) = 0.9, 1H, HC(35)); 6.78 (s, 1H, HC(31)); 6.30 (dd, 3J(34,33) = 3.3, 3J(34,35) = 1.8, 1H, HC(34)); 6.28 (dd, 3J(33,34) = 3.2, 4J(33,35) = 0.9, 1H, HC(33)); 6.28 (d, 4J(4A,31) = 0.7, 1H, HC(4)); 6.18 (d, 4J(4B,31) = 1.3, 1H, HBC(4)); 2.33 (s, 3H, H3C(1)); 2.08 (s, 3H, H3C(37)). 13C-NMR (100 MHz, CDCl3, 298 K): 197.5 (C(2)); 170.0 (C(36)); 151.2 (C(32)); 145.6 (C(3)); 143.7 (C(35)); 127.0 (C(4)); 111.1 and 110.3 (C(33)) and (C(34)); 66.2 (C(31)); 26.5 (C(1)); 21.6 (C(37)). EI-MS: 208 (0.8, [M]+), 105 (3), 97 (7), 88 (10), 86 (60), 85 (5), 84 (100), 83 (7), 82 (4), 78 (4), 77 (5), 70 (2), 68 (3), 55 (5), 51 (37), 50 (4), 49 (52), 48 (5), 47 (16), 38 (2), 36 (3). DCI-MS: 210 (10, [M + 2]+), 209 (83, [M + 1]+), 208 (26, [M]+), 190 (6), 187 (5), 185 (13), 167 (27), 166 (100), 165 (79), 151 (18), 150 (50), 149 (99), 148 (66), 137 (7), 123 (9), 107 (5), 106 (8), 105 (10), 97 (7), 95 (5), 78 (9), 77 (6), 65 (5), 63 (5), 55 (6), 43 (25). Anal. calc. for C11H12O4 (208.21): C 63.45, H 5.81; found: C 63.17, H 5.89.

Ethyl 2-acetoxy-3-acetyl-3-butenoate (23).

To a solution of ethyl 3-acetyl-2-hydroxy-3-butenoate (1.72 g, 10 mmol) in dry methylene dichloride (50 ml) was added pyridine (0.89 ml, 11 mmol) and acetyl chloride (0.78 ml, 11 mmol) at 0° C. Then the mixture was stirred for 1h, treated with 3.7 % HCl (50 ml) and the aqueous phase extracted with methylene dichloride (2 x 20 ml). The combined organic phases were dried over Na2SO4. Evaporation of solvent furnished practically pure product (1.88 g, 88 %) which was further purified by bulb-to-bulb distillation (temperature 100 - 110 °C, 6.10-2 mm Hg) to give a colourless oil 23 (1.71 g, 80 %).

B.p. 100-110 °C, 6.10-2 mm Hg. IR (film, KBr): 2985w, 2941w, 1748s, 1687s, 1639w, 1434w, 1372s, 1324m, 1231s, 1208s, 1148w, 1121w, 1097w, 1063s, 1032m, 980w, 938w, 910w, 860w, 604w, 498w, 488w, 409w. 1H-NMR (400 MHz, CDCl3, 298 K): 6.32 (d, 2J(4A,4B) = 0.4, 1H, HAC(4)); 6.19 (dd, 4J(4A,2) = 0.7, 2J(4B,4A) = 0.4, 1H, HBC(4)); 6.00 (d, 4J(2,4A) = 0.7, 1H, HC(2)); 4.20 (q, 3J(11,12) = 7.1, 2H, H2C(11)); 2.39 (s,3H, H3C(32)); 2.14 (s, 3H, H3C(22)); 1.24 (t, 3H, H3C(12)). 13C-NMR (100 MHz, CDCl3, 298 K): 196.3 (C(2)); 169.7 (C(32')); 168.2 (C(32)); 143.0 (C(3)); 129.5 (C(4)); 69.4 (C(31)); 61.8 (C(33)); 25.6 (C(1)); 20.6 (C(33')); 13.9 (C(34)). EI-MS: 215 (1, [M + 1]+), 171 (4), 129 (4), 127 (6), 126 (3), 113 (3), 111 (4), 108 (3), 101 (4), 100 (10), 99 (40), 98 (4), 88 (4), 86 (25), 85 (18), 84 (29), 83 (5), 71 (5), 70 (9), 69 (5), 67 (4), 57 (4), 55 (6), 51 (12), 49 (11), 47 (4), 45 (6), 44 (100), 43 (21), 42 (8), 40 (12). DCI-MS: 233 (12, [M + 19]+), 232 (100, , [M + 18]+), 216 (7), 215 (73), 174 (2), 172 (2), 169 (2), 157 (4), 155 (3). Anal. calc. for C10H14O5 (214.22): C 56.07, H 6.59; found: C 56.09, H 6.80.

(E)-3-(4-nitrobenzoxymethyl)-4-(2-furanyl)-3-buten-2-one (25).

To a solution of Ph3P (818 mg, 3.12 mmol) and 4-nitrobenzoic acid (521 mg, 3.12 mmol) in THF (20 ml) was added triethylamine (430 ml, 3.12 mmol). The resulting clear solution was cooled at - 10 °C, and DEAD (490 ml, 3.12 mmol) was added over a period of 5 min. To this solution was added 3-[(2-furanyl)-hydroxymethyl]-3-buten-2-one (0.346 g, 2.08 ml of 1 M solution in benzene, 2.08 mmol) in THF (1 ml) over a period of 15 min. When TLC analysis showed the complete consumption of starting material (8 h), the reaction was placed at 0 °C (15 min) and then diluted with ether (120 ml) and water (10 ml). The organic phase was washed with water (20 ml) and 1.0 M NaOH (2 x 20 ml). The aqueous layers were extracted with ether (2 x 20 ml), and combined organic layers were washed with saturated aqueous NaHCO3 (20 ml) and saturated aqueous NaCl (20 ml). The organic layer was dried over MgSO4, and concentrated under reduced pressure. The residue was preadsorbed on silica gel and purified by flash chromatography (EtOAc/heptane 1:2) to afford of product 25 (466 mg, 71 %) as a slightly yellow solid which, for anal. purposes, was crystallised from hexane/AcOEt 20:1. Slightly yellow crystals.

M.p. 136.0-136.5° (hexane/AcOEt 20:1). IR (KBr): 3110w, 3053w, 3016w, 1725s, 1658s, 1628m, 1608w, 1521s, 1472w, 1453w, 1421w, 1411w, 1392w, 1369m, 1352m, 1320w, 1276s, 1242s, 1208m, 1174w, 1161w, 1118m, 1104m, 1084w, 1073w, 1033w, 1013m, 962w, 940m, 924w, 886w, 870w, 841w, 817w, 784w, 751w, 738w, 717s, 600w, 588w, 492w. 1H-NMR (400 MHz, CDCl3, 298 K): 8.24 (dm, 3J(34,35) = 3J(34',35') = 9.1, 2H, HC(34,34')); 8.14 (dm, 3J(35,34) = 3J(35',34') = 9.1, 2H, HC(35,35')); 7.59 (ddd, 3J(44,43) = 1.8, 4J(44,42) = 0.7, 6J(44,4) = 0.4, 1H, HC(44)); 7.50 (s, 1H, HC(4)); 6.85 (ddd, 3J(42,43) = 3.5, 4J(42,44) = 0.7, 4J(42,4) = 0.4, 1H, HC(42)); 6.55 (ddd, 3J(43,42) = 3.5, 3J(43,44) = 1.8, 5J(43,4) = 0.3, 1H, HC(43)); 5.52 (s, 2H, HC(31)); 2.49 (s, 3H, HC(1)). 13C-NMR (100 MHz, CDCl3, 298 K): 198.1 (C(2)); 165.4 (C(32)); 151.2 (C(36)); 150.7 (C(41)); 147.2 (C(44)); 136.3 (C(33)); 131.4 (C(35,35')); 131.3 (C(4)); 130.6 (C(3)); 124.1 (C(34,34'); 119.6.(C(42)); 113.5 (C(43)); 60.3 (C(31)); 26.5 (C(1)). EI-MS: 315 (14, [M]+), 165 (100), 151 (47), 150 (73), 149 (53), 148 (95), 119 (61), 104 (76), 76 (46), 44 (68), 43 (93). HR-CI-MS: 316.0874 (MH+; calc. for C16H14NO6+: 316.0816).

(E)-3-Benzoxymethyl-4-(2-furanyl)-3-buten-2-one (26).

To a solution of Ph3P (818 mg, 3.12 mmol) and benzoic acid (381 mg, 3.12 mmol) in THF (20 ml) was added triethylamine (430 ml, 3.12 mmol). The resulting clear solution was cooled at - 10 °C, and DEAD (490 ml, 3.12 mmol) was added over a period of 5 min. To this solution was added 3-[(2-furanyl)-hydroxymethyl]-3-buten-2-one (0.346 g, 2.08 ml of 1 M solution in benzene, 2.08 mmol) in THF (1 ml) over a period of 15 min. When TLC analysis showed the complete consumption of the starting material (8 h), the reaction was placed at 0 °C (15 min) and then diluted with ether (120 ml) and water (10 ml). The organic phase was washed with water (20 ml) and 1.0 M NaOH (2 x 20 ml). The aqueous layers were extracted with ether (2 x 20 ml), and the combined organic layers were washed with saturated aqueous NaHCO3 (20 ml) and saturated aqueous NaCl (20 ml). The organic layer was dried over MgSO4, and concentrated under reduced pressure. The residue was preadsorbed on silica gel and purified by flash chromatography (EtOAc/Heptane 1 : 2) to afford of product 26 (360 mg, 64 %) as a slightly yellow oil which, for anal. purposes, was crystallised from hexane/AcOEt 20:1. White powder (332 mg, 59 %).

M.p. 88.5-89.0° (hexane/AcOEt 20:1). IR (KBr): 3144w, 3130w, 3062w, 3016w, 2969w, 2385w, 1712s, 1665s, 1637s, 1601m, 1584m, 1550w, 1506w, 1493w, 1471m, 1452s, 1424w, 1402w, 1388s, 1366s, 1346m, 1317m, 1275s, 1231s, 1206s, 1175m, 1159m, 1148m, 1118s, 1071m, 1027m, 1013s, 964m, 948s, 923m, 884m, 859m, 829m, 806w, 768w, 752s, 713s,672m, 591m, 528w, 480w, 456w. 1H-NMR (400 MHz, CDCl3, 298 K): 8.00 - 7.97 (dm, 2H, HC(34,34'); 7.58 (ddd, 3J(44,43) = 1.8, 4J(44,42) = 0.7, 6J(44,4) = 0.3, 1H, HC(44)); 7.55 - 7.50 (tm, 1H. HC(36)); 7.49 (s, 1H, HC(4)); 7.42 - 7.37 (tm. 2H. HC(35,35'); 6.84 (ddd, 3J(42,43) = 3.5, 4J(42,44) = 0.7, 4J(42,4) = 0.4, 1H, HC(42)); 6.53 (ddd, 3J(43,42) = 3.5, 3J(43,44) = 1.8, 5J(43,4)= 0.4, 1H, HC(43)); 5.47 (s, 2H, H2C(31)); 2.48 (s, 3H, H3C(1)). 13C-NMR (100 MHz, CDCl3, 298 K): 197.6 (C(2)); 166.6 (C(32)); 150.2 (C(41)); 146.2 (C(44)); 132.9 (C(36)); 130.5 (C(3)); 130.2 (C(4)); 130.2 (C(33)); 129.6 (C(34,34'); 128.3 (C(35,35')); 118.4 (C(42)); 112.7 (C(43)); 59.0 (C(31)); 26.0 (C(1)). EI-MS: 270 (5, [M]+), 166 (9), 165 (55), 148 (19), 106 (11), 105 (90), 91 (11), 78 (23), 77 (100), 76 (7), 74 (6), 65 (9), 63 (8), 62 (5), 44 (97), 40 (17). DCI-MS: 288 (1, [M + 18]+), 272 (5, [M + 2]+), 271 (11, [M + 1]+), 167 (8), 166 (100), 165 (19), 151 (4), 150 (13), 149 (87), 148 (7), 105 (15), 94 (4), 78 (3), 77 (3). Anal. calc. for C16H14O4 (270.28): C 71.10, H 5.22; found: C 71.14, H 5.38.

(E,Z)-Ethyl 3-(2,4-dinitrobenzoxymethyl)-4-oxo-2-pentenoate (27).

To a solution of Ph3P (818 mg, 3.12 mmol) and 2,4-dinitrobenzoic acid (662 mg, 3.12 mmol) in THF (20 ml) was added triethylamine (430 ml, 3.12 mmol). The resulting clear solution was cooled at - 10 °C, and DEAD (490 ml, 3.12 mmol) was added over a period of 5 min. To this solution was added ethyl 3-acetyl-2-hydroxy-3-butenoate (358 mg, 2.08 mmol) in THF (1 ml) over a period of 15 min. When TLC analysis showed the complete consumption of starting material (16 h), the reaction was placed at 0 °C (15 min) and then diluted with ether (120 ml) and water (10 ml). The organic phase was washed with water (20 ml) and 1.0 M NaOH (2 x 20 ml). The aqueous layers were extracted with ether (2 x 20 ml), and combined organic layers were washed with saturated aqueous NaHCO3 (20 ml) and saturated aqueous NaCl (20 ml). The organic layer was dried over MgSO4, and concentrated under reduced pressure. The residue was preadsorbed on silica gel and purified by flash chromatography (heptane/AcOEt 2:1) to afford of product 27 (167 mg, 22 %, E/Z 3:2) as a slightly yellow oil.

IR (film, KBr): 3109w, 3059w, 2985w, 2941w, 1743s, 1723s, 1691s, 1651w, 1605m, 1542s, 1447m, 1350s, 1283s, 1245s, 1200s, 1157m, 1133m, 1113m, 1058m, 1039m, 952w, 910w, 860w, 835m, 816w, 778w, 736m, 490w. DCI-MS: 385 (14, [M + 19]+), 384 (100, [M + 18]+), 368 (13), 367 (65), 234 (22), 196 (8), 195 (24), 194 (11), 190 (13), 174 (14), 173 (38), 172 (8), 171 (10), 165 (7), 157 (24), 156 (15), 96 (29), 44 (14). HR-CI-MS: 367.0785 (MH+; calc. for C15H15N2O9+: 367.0772).

(E)-Ethyl 3-(2,4-dinitrobenzoxymethyl)-4-oxo-2-pentenoate (27a). 1H-NMR (400 MHz, CDCl3, 298 K): 8.76 (d, 4J(35,37) = 2.2, 1H, HC(35)); 8.51 (dd, 3J(37,38) = 8.4, 4J(37,35) = 2.2, 1H, HC(37)); 7.92 (d, 3J(38,37) = 8.4, 1H, HC(38)); 6.79 (s, 1H, HC(2)); 5.56 (s, 2H, H2C(31)); 4.30 (q, 3J(11,12) = 7.1, 2H, H2C(11)); 2.44 (s, 3H, H3C(5)); 1.34 (t, 3J(12,11) = 7.1, 3H, H3C(12)). 13C-NMR (100 MHz, CDCl3, 298 K): 198.3 (C(4)); 165.3 (C(1)); 163.8 (C(32)); 149.6 and 148.6 (C(34)) and (C(36)); 145.5 (C(3)); 133.3 (C(33)); 132.1 (C(38)); 132.0 (C(2)); 128.2 (C(37)); 120.2 (C(35)); 62.5 (C(11)); 59.9 (C(31)); 27.0 (C(5)); 14.8 (C(12)).

(Z)-Ethyl 3-(2,4-dinitrobenzoxymethyl)-4-oxo-2-pentenoate (27b). 1H-NMR (400 MHz, CDCl3, 298 K): 8.84 (d, 4J(35,37) = 2.2, 1H, HC(35)); 8.57 (dd, 3J(37,38) = 8.4, 4J(37,35) = 2.2, 1H, HC(37)); 7.96 (d, 3J(38,37) = 8.4, 1H, HC(38)); 6.01 (t, 4J(2,31) = 1.5, 1H, HC(2)); 5.06 (d, 4J(31,2) = 1.5, 2H, H2C(31)); 4.21 (q, 3J(11,12) = 7.1, 2H, H2C(11)); 2.41 (s, 3H, H3C(5)); 1.29 (t, 3J(12,11) = 7.1, 3H, H3C(12)). 13C-NMR (100 MHz, CDCl3, 298 K): 203.2 (C(4)); 165.1 (C(1)); 163.8 (C(32)); 151.8 (C(3)); 149.9 and 148.5 (C(34)) and (C(36)); 132.8 (C(33)); 132.0 (C(38)); 128.6 (C(37)); 121.2 (C(2)); 120.5 (C(35)); 66.4 (C(31)); 62.2 (C(11)); 30.7 (C(5)); 14.7 (C(12)).

We thank H. Bursian and Dr. S. Claude from our department for the NMR spectra and Dr. G.-M. Dubin and C. Poilart for the measurement of the MS. We thank Professor T. Jenny and F. Nydegger from the University of Fribourg for the high resolution MS. P.B. thanks the Swiss National Science Foundation and the Ciba-Geigy-Jubiläumsstiftung for a fellowship.