Synthesis of (+)-shikimic acid
1627
as chiral shift reagent]. IR (CHCI3): 3030, 2980, 1700, 1370, 1290, 1260, 1120, 1040, 970, and 840.
IH NMR (CDCI3) 6:1.34 (s, 9H), 2.39 (s, 3H), 6.70 (s, IH), 6.82 (s, 1H), 7.27 (half of an AA'BB'
system, 2H) and 7.58 (half of an AA'BB' system, 2H). 13C NMR (CDCI3) 6: 21.3, 27.6, 83.1, 126.2,
127.4, 129.6, 139.7, 142.2, 148.2, and 160.7.MS (EI): 266 (10.9, M+), 210 (34.6), 162 (60.3), 149
(33.7), 139 (100.0), 123 (23.0), 91 (37.8), 77 (13.2), 65 (25.0), and 57 (90.7). HRMS: exact mass
calcd for C14H1803S (M+) 266.0976, found 266.0977.
General procedure for the Diels-Alder reactions of I and 2 with furan under high pressures
In a polyethylene high pressure tube were placed dienophile 1 or 2 (150-200 mg) in furan (1 ml).
The reaction was pressured at 4 Kbar for 5 days at rt. Then, the mixture was carefully concentrated
(without heating) and the residue was immediately analyzed by I H NMR. The mixture of adducts
3 or 4 (mainly endo adducts) was purified by flash chromatography at low temperature (0-5°C)
(hexane-ethyl acetate 4:1). Conversion=60-65%. For the ratio of isomers see Table 1.
(RI, 82, R4,SS) 2-Benzyl 2-p-tolylsulfinyl- 7-oxabicyclo[2.2.1 ]hept-5-ene-2-carbo~'late endo-3A
IH NMR (CDCI3) 6:1.90 (d, 1H, J=12.5 Hz), 2.39 (s, 3H), 2.78 (dd, 1H, J=4.7 y 12.6 Hz), 4.81
(AB system, 2H, J=12.4 Hz), 5.15 (m, 1H), 5.27 (m, 1H), 6.17 (dd, 1H, J=5.6 y 1.8 Hz), 6.65 (dd,
1H, J=l.8 and 5.6 Hz), 7.29 (half of an AA'BB' system, 2H, J=8.1 Hz) and 7.55 (half of an AA'BB'
system, 2H).
(S I,R2,84, SS) 2-Benzyl 2-p-tolylsulfinyl- 7-oxabicyclo[2.2.1 ]hept-5-ene-2-carbo©,late endo-3B
IH NMR (CDCI3) tS: 1.93 (d, 1H, J=12.5 Hz), 2.15 (dd, IH, J=4.7 and 12.5 Hz), 2.37 (s, 3H), 4.71
y 4.87 (AB system, 2H, J=12.1 Hz), 5.18 (bd, 1H, J=7.2 Hz), 5.64 (d, 1H, J=l.1 Hz), 6.15 (dd, IH,
J= 1.7 and 5.6 Hz), 6.53 (dd, 1H, J=l.6 and 5.5 Hz), 7.17-7.35 (m, 7H) and 7.45 (half of an AA'BB'
system, 2H).
(R!,S2,R4, Ss) 2-t-Butyl 2-p-tolylsulfinyl-7-oxabicyclo[2.2. l ]hept-5-ene-2-carboxylate endo-4A
[et]D 2°=- 124.5 (c---l, CHCI3). IR (CHC13): 2960, 1710, 1360, 1270, 1150, 1050, 910 and 840. IH
NMR (CDCI3) 8: i .26 (s, 9H), 1.95 (d, 1H, J-- 12.6 Hz), 2.41 (s, 3H), 2.73 (dd, 1H, J=4.7 and 12.6 Hz),
5.15 (dd, IH, J=4.7 and 1.8 Hz), 5.29 (dd, IH, J=l.8 Hz), 6.27 (dd, 1H, J=l.8 and 5.6 Hz), 6.56 (dd,
1H, J=l.8 and 5.6 Hz), 7.29 (half of an AA'BB' system, 2H) and 7.55 (half of an AA'BB' system,
2H, J=8.2 Hz). 13C NMR (CDCI3): 21.6, 27.5, 29.7, 76.6, 79.3, 82.6, 125.9, 129.2, 132.9, 137.9,
140.1, 142.3 and 165.6. HRMS: exact mass calcd for C18H22048 (M+) 334.1239, found 334.1239.
(S1,R2,$4, Ss) 2-t-BuO,l 2-p-tolylsulfinyl- 7-oxabicyclo[ 2.2.1 ]hept-5-ene-2-ca rboxylate endo-4B
[~X]D20=+33.25 (c=1.2, CHCI3). IR (CHCI3): 2990, 1710, 1370, 1240, 1150, 1050, 910 and 840.
IH NMR (CDCI3) 8:1.26 (s, 9H), 1.82 (d, 1H, J=12.5 Hz), 2.15 (dd, IH, J=4.7 and 12.5 Hz), 2.37 (s,
3H), 5.10 (dd, 1H, J=l.1 and 4.7 Hz), 5.54 (d, 1H, J=l. l Hz), 6.32 (dd, 1H, J=l.8 y 5.7 Hz), 6.53 (dd,
1H, J=l.8 and 5.7 Hz), 7.25 (half of an AA'BB' system, 2H) and 7.52 (half of an AA'BB' system,
2H). 13C NMR (CDC13) ~i:21.1, 27.6, 32.1, 79.6, 79.8, 82.2, 125.1, 129.2, 133.0, 137.1, 139.3, 141.6
and 165.0. MS (EI): 334 (0.2, M+), 266 (11.0), 210 (38.0), 193 (22.1), 162 (61.4), 139 (98.0), 123
(24.6), 91 (42.7), 77 (16.0) and 57 (100.0). HRMS: exact mass calcd for C18H2204S (M+) 334.1239,
found 334.1238.
(S1, $4) t-Butyl 7-oxabicyclo[2.2.1]hept-5-ene-2-carbox3'late endo-5+exo-5
To a solution of endo-4B (440 mg, 1.32 mmol, 1.0 equiv) in THF (10 ml) cooled to - 7 8 ° C and
under argon atmosphere, were added sequentially MeOH (270 lal, 6.60 mmol, 5.0 equiv), DMPU (794
Ill, 6.60 mmol, 5.0 equiv) and freshly prepared SmI2 0.1M (51 ml, 5.1 mmol, 4.0 equiv). The mixture
was stirred for 1 h and was allowed to stand at 0°C. Then, a solution of 30% Na2SO3 (40 ml) was
added, and the mixture was extracted with CH2C12 (3×50 ml). The combined organic layers were
dried and concentrated. The residue was purified by flash chromatography (hexane-ethyl acetate 8:1)
to give 220 mg of 5 as a yellow oil. Yield: 85%. IR (CHCI3): 2940, 1710, 1450, 1370, 1220, 1150,