Selective Silylation of D-Mannitol
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D-Mannitol 1,6-Di-(tert-butyldiphenylsilyl)-2:4, 3:5-O2:O4,O3:O5bis(phenyl-
boronate) (2). The title compound was prepared according to the method described
for the preparation of 1, using D-mannitol (2.5 g, 14 mmol), phenylboronic acid (3.4 g,
28 mmol), DMF (150 mL), toluene (150 mL), imidazole (5.6 g, 83 mmol) and
TBDPSCl (8.3 g, 30 mmol). After being allowed to warm to room temperature, the
reaction mixture was stirred overnight. Following the addition of water (750 mL), the
reaction mixture was extracted with dichloromethane. The organic layers were washed
with water then brine and dried over MgSO4. After removal of some of the solvent in
vacuo, the product crystallized as a light tan solid (6.2 g, 54 %); mp 148–149 ꢀC.
Single crystals suitable for X-ray analysis were grown by slow evaporation from an
acetone solution. IR (KBr disk): n [cmÀ 1] = 2932 (C—H), 2858 (C—H), 1601 (C=C),
1472 (C=C), 1444 (B—C), 1428 (C=C), 1334 (B—O), 1303 (C—O), 1151 (C—O),
1
1113 (Si O), 1022, 993, 937, 842, 822, 805, 700, 635, 611, 502. H NMR (300 MHz;
CDCl3): d = 7.86–7.92 (m, 4H, oArH-B), 7.67–7.79 (m, 8H, oArH-Si), 7.29–7.51 (m,
18H, mArH-Si, pArH-Si, pArH-B and mArH-B ), 4.97 (br s, 2H, 3-H, 4-H), 4.42–4.51
(m, 2H, 2-H, 5-H), 4.06 (dd, J1a,1b = 4.5 Hz, J1a,2 = 11.1 Hz, 2H, 1a-H, 6a-H), 3.99 (dd,
J1b,2 = 3.2 Hz, J1b,1a = 11.1 Hz, 2H, 1b-H, 6b-H), 1.06 (s, 18H, Si-C(CH3)3). 13C NMR
(75MHz, CDCl3): d = 135.8, 135.7 (Si-oC-arom.), 134.2 (B-oC-arom.), 133.1, 132.5
(Si-iC-arom.), 130.7 (B-mC-arom.), 130.1, 130.0 (Si-pC-arom.), 128.0, 127.9 (Si-mC-
arom.), 127.6 (B-mC-arom.), 75.0 (C-2, C-5), 67.7 (C-3, C-4), 65.1 (C-1, C-6), 26.9
(Si-C(CH3)3), 19.3 (SiC). C–B signals not observed due to broadening.
Anal. Calcd for C50H56B2O6Si2: C, 72.29; H, 6.79. Found: C, 72.55; H, 7.00.
Crystal structure determination of 2: C56H68B2O8Si2, Mr = 946.94, mono-
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clinic, space group P1211 (no. 4), a = 11.8257(1), b = 12.6022 (1), c = 17.8951 (2) A,
3
3
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b = 98.273 (1)ꢀ, V = 2639.15 A , Z = 2, Dx = 1.192 g/cm , F(000) = 1012, T = 173 K,
Enraf Nonius FR590 diffractometer, graphite monochromator with CCD detector,
l(Mo-Ka) = 0.71073 A, m = 0.12 mm–1, colourless crystal, size 0.23 Â 0.25 Â 0.20
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mm3, f scans with o scans to fit asymmetric unit, 32361 intensities collected
3.08<q<28.29ꢀ, À15<h<15, À 16<k<16, À 21<l<23, Lp correction, no absorption
correction, 12958 unique intensities (Rint = 0.0638). Structure solved by direct methods,
full-matrix least-squares refinement based on F2 and 613 parameters, all but H atoms
refined anisotropically, H atoms refined with riding model on idealized positions.
Refinement converged at R1(F) = 0.0435, oR2(F2, all data) = 0.1018, S = 1.0440,
absolute structure parameter (Flack) À0.08(6).
D-Mannitol 1,6-Di-(tert-butyldimethylsilyl) ether (3). A solution of 1 (0.51 g,
0.88 mmol) in ethyl acetate/acetone (1:1, 20 mL) was treated with aqueous hydrogen
peroxide (30 wt%, 0.54 mL) and the mixture stirred for 4 h. Evaporation of the solvent
yielded a yellow oil containing a white precipitate (0.52 g). A solution of the crude
product in ethyl acetate was washed three times with NaOH (1 moldmÀ 3) then dried
over MgSO4. Removal of the solvent yielded a clear oil which was purified using flash
column chromatography (40% EtOAc/hexane) to give the pure product as a white solid
(0.12 g, 62 %); mp 58–60 ꢀC. [a]2n0 < j1j (c 0.050, CHCl3). IR (nujol): n [cmÀ 1] =
1
3384 (O—H), 1255 (Si—Me), 1111 (Si O), 1058 (C—O), 837 (Si—Me), 777. H
NMR (300 MHz; CDCl3): d = 3.71–3.88 (m, 8H, 1-H, 2-H, 3-H, 4-H, 5-H, 6-H),
3.31–3.38 (br d, J2,OH = 5.7 Hz, 2H, CH2CH(OH), no signal upon D2O exchange),