Benzylidene b-Mannosylation Without Triflate?
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(126 MHz, CDCl3): d 139.2, 138.6, 137.7, 129.0–127.6 (m, Ar), 126.2, 101.3, 96.3
(C-1), 82.6, 82.4, 81.7, 81.3, 79.6, 78.9, 76.2, 75.5, 75.4, 73.5, 69.3, 69.1, 66.2,
62.6, 33.9, 33.6, 32.1, 31.7, 25.8, 24.5, 24.3, 24.2.
The donor 3a (12 mg, 18 mmol), cyclohexanol (9.4 mL, 89 mmol), and NMP
(600 mL) were placed in an Eppendorf tube and heated to 608C on an Eppendorf
Thermomixer 5436. After 27 h EtOAc (20 mL) was added, and the reaction
mixture was washed with brine (2 ꢀ 20 mL), NaOH (0.5 M, 2 ꢀ 20 mL), and
again with brine (2 ꢀ 20 mL). The organic phase was dried with Na2SO4, evap-
orated, and purified by VLC (EtOAc-toluene 1:60 ! 1:5) to give the title
compound as an off-white powder (5.0 mg, 53%, a/b 1.7:1).
4-Methoxyphenyl 2,3:4,6-Di-O-benzylidene-a-D-
mannopyranoside (6)
In a 50-mL flask 4-methoxyphenyl mannoside (synthesized from mannose
according to[4,22,23]
) (230 mg, 0.80 mmol), benzaldehyde dimethylacetal
(600 mL, 4.0 mmol) and camphorsulfonic acid (CSA, 19 mg, 0.08 mmol) were
dissolved in CH3CN (20 mL). A part (15 mL) of the reaction mixture was
removed by distillation and Et3N (five drops) were added followed by evapor-
ation. MeOH (10 mL) was added and heated to boiling where a white solid
(6-exo) precipitated from the solution and was filtered off. When the mother
liquor was left to cool down the corresponding endo-isomer precipitated out
and was filtered off as a white powder (308 mg, 83%, endo/exo 1:3.3).
Data of 6-endo: mp (endo) 131–1328C; [a]D ¼ 36.0 (c 8.83 ꢀ 1023 CHCl3). 1H
NMR (300 MHz, CDCl3): d 7.60–7.34 (m, 10H, ArH), 7.03–7.00 (m, 2H, ArH),
6.88–6.85 (m, 2H, ArH), 6.05 (s, 1H, PhCHO2), 5.82 (s, 1H, H-1), 5.54 (s, 1H,
PhCHO2), 4.65 (dd, 1H, J ¼ 7.5 Hz, J ¼ 6.2 Hz, H-3), 4.55 (d, 1H, J ¼ 6.2 Hz,
H-2), 4.23 (dd, 1H, J ¼ 10.2 Hz, J ¼ 5.1 Hz, H-6), 4.01 (ddd, 1H, J ¼ 10.2 Hz,
J ¼ 9.8 Hz, J ¼ 5.1 Hz, H-5), 3.82 (dd, 1H, J ¼ 9.8 Hz, J ¼ 7.5 Hz, H-4), 3.79
(s, 3H, OMe), 3.72 (t, 1H, J ¼ 10.2 Hz, H-60). 13C NMR (75 MHz, CDCl3): d
155.4, 149.9, 137.3, 137.1, 129.6–126.2 (m, benzylidene), 2 ꢀ 118.1, 2 ꢀ 114.9,
104.4, 102.0, 97.0 (C-1), 80.5, 78.5, 74.3, 68.9, 61.4, 55.8. ES-HR-MS: m/z calcd
for C27H26O7 462.1679; [M þ H]þ: 463.1757; found: 463.1755.
Data of 6-exo: mp (exo) 189–1928C; 1H NMR (300 MHz, CDCl3): d 7.57–7.35
(m, 10H, ArH), 7.00–6.97 (m, 2H, ArH), 6.86–6.83 (m, 2H, ArH), 6.35 (s, 1H,
PhCHO2), 5.75 (s, 1H, H-1), 5.66 (s, 1H, PhCHO2), 4.81 (dd, 1H, J ¼ 7.7 Hz,
J ¼ 5.6 Hz, H-3), 4.39 (d, 1H, J ¼ 5.6 Hz, H-2), 4.29 (dd, 1H, J ¼ 10.4 Hz,
J ¼ 4.5 Hz, H-6), 4.04 (ddd, 1H, J ¼ 10.4 Hz, J ¼ 9.7 Hz, J ¼ 4.5 Hz Hz, H-5),
3.97 (dd, 1H, J ¼ 9.7 Hz, J ¼ 7.7 Hz, H-4), 3.81 (t, 1H, J ¼ 10.4 Hz, H-60), 3.78
(s, 3H, OMe). 13C NMR (75 MHz, CDCl3): d 155.4, 150.0, 138.6, 137.2, 129.6–
126.2 (m, benzylidene), 2 ꢀ 118.1, 2 ꢀ 114.9, 103.3, 102.2, 97.1 (C-1), 77.6,
75.8, 75.6, 68.9, 61.3, 55.8. ES-HR-MS: m/z calcd for C27H26O7: 462.1679;