LiBF₄-Mediated Conversion of Aldehydes to gem-Diacetates

Abstract

An efficient and highly selective method for the conversion of aldehydes to gem-diacetates is described using lithium tetrafluoroborate under mild reaction conditions. Due to the neutral reaction conditions, this method is compatible with acid-sensitive protecting groups such as acetonides, carbamates, THP and TBDMS ethers present in the substrate.

Key words

lithium tetrafluoroborate - aldehydes - gem-diacetates

References

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9

Preparation of gem -Diacetates: A mixture of aldehyde (5 mmol) freshly distilled acetic anhydride (5 mmol) and LiBF₄ (5 mmol) in acetonitrile (15 mL) was stirred at r.t. for an appropriate time (Table). After complete conversion, as indicated by TLC, the reaction mixture was poured into sat. sodium bicarbonate solution (30 mL) and extracted with ethyl acetate (2 × 15 mL). The combined organic layers were dried over anhyd Na₂SO₄ and concentrated in vacuo. The resulting product was recrystallized from ethyl acetate-hexane (2:8) to afford pure 1,1-diacetate.
Spectral data. 3b: Solid, mp 72-74 °C, ¹H NMR (CDCl₃): δ = 2.18 (s, 6 H), 3.88 (s, 3 H), 3.89 (s, 3 H), 6.83 (d, 1 H, J = 8.0 Hz), 7.03 (s, 1 H), 7.08 (d, 1 H, J = 8.0 Hz), 7.58 (s, 1 H). MS (EI): m/z = 268 [M⁺], 167, 139, 95, 77, 43. IR (KBr): 3049, 2955, 1745, 1687, 1495, 1243, 1010, 968
cm^-1. 3d: Solid, mp 66-67 °C (ref. [6] 66-67). ¹H NMR (CDCl₃): δ = 2.15 (s, 6 H), 7.10 (dd, 1 H, J = 5.0, 4.5 Hz), 7.30 (d, 1 H, J = 4.5 Hz), 7.40 (d, 1 H, J = 5.0 Hz), 7.90 (s, 1 H). MS (EI): m/z = 214 [M⁺], 171, 155, 112, 85. IR(neat): 3050, 2960, 1757, 1480, 1245, 1017, 845 cm^-1. 3f: Solid, mp 84-85 °C (ref. [5] 84-86). ¹H NMR (CDCl₃): δ = 2.15 (s, 6 H), 5.95 (dd, 1 H, J = 16.5 and 7.2 Hz), 6.85 (d, 1 H, J = 16.5 Hz), 7.20-7.45 (m, 6 H). MS (EI): m/z = 234 [M⁺], 191, 175, 132, 101, 91. IR (KBr): 3055, 2955, 1750, 1680, 1490, 1240, 1015, 970 cm^-1. 3h: ¹H NMR (CDCl₃): δ = 2.20 (s, 6 H), 7.80 (t, 2 H, J = 8.2 Hz), 7.60 (s, 1 H), 7.65 (m, 1 H), 7.95 (d, 2 H, J = 8.2 Hz). MS (EI): m/z = 236 [M⁺], 193, 105, 77, 51, 43. IR (KBr): 3055, 2970, 1760, 1720, 1235, 1020 cm^-1. 3i: ¹H NMR (CDCl₃): δ = 2.16 (s, 6 H), 6.98-7.05 (m, 3 H), 7.08-7.20 (m, 3 H), 7.30-7.38 (m, 3 H), 7.60 (s, 1 H). MS (EI): m/z = 300 [M⁺], 198, 170, 142, 115, 77, 43. IR (KBr): 3053, 2965, 1748, 1680, 1490, 1240, 1015, 967 cm^-1. 3k: Liquid, 127-129/2mm (ref. [6] 128/2mm). ¹H NMR (CDCl₃): δ = 0.95 (t, 3 H, J = 6.8 Hz), 1.25-1.50 (m, 6 H), 1.75-1.83 (m, 2 H), 2.15 (s, 6 H), 6.70 (t, 1 H, J = 6.8 Hz). MS (EI):
m/z = 202 [M⁺], 159, 143, 100, 84. IR(neat): 3040, 2955, 1750, 1685, 1485, 1245, 1020, 965 cm^-1.