A Convenient and Versatile Preparation of Unsymmetrical Bis-metallic ­Isobutene Derivatives

Abstract

Synthetically useful unsymmetrical bis-silyl or silyl-stannyl isobutene derivatives are conveniently prepared from ­selenoisobutene 5, a versatile equivalent of the isobutene dianion. Sequential treatment of this selenated compound with n-butyl­lithium and the required chlorosilanes or chlorostannanes leads ­efficiently to the corresponding functionalized isobutenes.

Key words

isobutene - silicon - tin - selenium - allylation

References and Notes

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8

Typical Experimental Procedure - Preparation of 6b.
To a solution of diselenide 5 (2.66 g, 10.99 mmol) in THF (50 mL) at -78 °C was added n-BuLi (4.39 mL, 10.99 mmol, 2.5 M solution in hexane). The deep yellow solution was stirred at -78 °C for 30 min, then PhMe₂SiCl (2 mL, 12.09 mmol) was added dropwise. The colorless reaction mixture was allowed to warm up to r.t. over 1 h, then diluted with Et₂O (100 mL) and washed with brine (3 × 50 mL). The organic layer was dried (MgSO₄), filtered and evaporated in vacuo. The residue was purified by column chromatography (silica gel, PE-Et₂O = 50:1) to give 6b as a yellow oil (2.46 g, 79%). ¹H NMR (300 MHz, CDCl₃): δ = 7.45-7.60 (2 H, m), 7.30-7.45 (3 H, m), 4.67 (1 H, s), 4.61 (1 H, s), 2.93 (2 H, s), 1.93 (3 H, s), 1.84 (2 H, s), 0.33 (6 H, s). ¹³C NMR (62.5 MHz, CDCl₃): δ = 142.82, 138.83, 133.78, 129.27, 127.96, 111.11, 33.33, 24.07, 4.19, -2.74. IR (film): 3068, 3049, 2955, 2922, 1625, 1426, 1248, 1113, 834, 729. MS (CI⁺): m/z (%) = 285.4 (11), 283.7 (22), 269.0 (41), 266.8 (26), 207.0 (100), 204.8 (60), 190.4 (12), 189.1 (30), 175.0 (12), 135.0 (82).
Preparation of 3c.
To a solution of 6b (2.27 g, 7.99 mmol) in THF (40 mL) at -78 °C was added n-BuLi (3.20 mL, 7.99 mmol, 2.5 M solution in hexane). The yellow solution was stirred at
-78 °C for 30 min, then Bu₃SnCl (2.39 mL, 8.80 mmol) was added dropwise. The colorless reaction mixture was allowed to warm up to r.t. over 1 h, then diluted with Et₂O (100 mL) and washed with brine (3 × 25 mL). The organic layer was dried (Na₂SO₄), filtered and evaporated in vacuo. The residue was purified by horizontal distillation of the volatile impurities (160 °C, 2.3 mbar) and column chromatography (neutral alumina, PE) to give 3c as a yellow oil (2.80 g, 73%). ¹H NMR (300 MHz, CDCl₃): δ = 7.50-7.60 (2 H, m), 7.30-7.40 (3 H, m), 4.40 (1 H, d, J = 2.0 Hz), 4.23 (1 H, d, J = 2.0 Hz), 1.65 (2 H, s), 1.63 (2 H, s), 1.20-1.60 (18 H, m), 0.60-1.00 (9 H, m), 0.33 (6 H, s). ¹³C NMR (62.5 MHz, CDCl₃): δ = 147.01, 139.58, 133.79, 129.08, 127.88, 103.90, 29.34, 28.40, 27.57, 21.89, 13.90, 9.66, -2.71. IR (film): 3069, 2956, 2925, 2871, 2852, 1614, 1463, 1248, 1113, 844, 726, 697. MS (APCI⁺): m/z (%) = 322.6 (100), 290.90 (70), 266.7 (86), 234.9 (22), 210.8 (45), 178.95 (22).