Novel Ligand-Free, Cobalt-Catalyzed [2+2+2] Cycloadditions: Syntheses of 1,4-Disilatetralines and 1,3-Disilaindanes

Abstract

A new and simple catalytic system for efficient [2+2+2] alkyne cycloadditions was discovered. Cobalt(II) iodide in acetonitrile, in the presence of zinc powder, can catalyze arene synthesis at room temperature, and a 2.5% catalyst load gives almost complete consumption of the starting materials within ca. five minutes. Sterically hindered diynes can be efficiently coupled with terminal and internal monoynes. A large excess of monoyne is not required. Relatively small amounts of byproducts make the isolation of the target compound straightforward. This method allows efficient one-step syntheses of 1,4-disilatetralines and 1,3-disilaindanes, which are hardly available using other methods.

alkyne cycloaddition - arene synthesis - silicon

References and Notes

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6-(Tetrahydropyran-2-yloxymethyl)-1,1,4,4-tetra-methyl-1,4-disila-1,2,3,4-tetrahydronaphthalene ( 3a): ¹H NMR (400.1 MHz, CDCl₃): δ = 0.199 (s, 6 H, 2 × SiCH₃), 0.207 (s, 3 H, SiCH₃), 0.210 (s, 3 H, SiCH₃), 0.99 (s, 4 H, SiCH₂CH₂Si), 1.44-1.58, 1.80-1.91 (m, 2 H, 4-CH₂ of THP), 1.50-1.63 (m, 2 H, 5-CH₂ of THP), 1.63-1.77 (m, 2 H, 3-CH₂ of THP), 3.51-3.57, 3.89-3.96 (m, 2 H, 6-CH₂ of THP), 4.47, 4.70 (AB system, J _AB = 12.1 Hz, 2 H, CCH₂O), 4.70 (t, J = 3.6 Hz, 1 H, 2-CH of THP), 7.34 [dd, A part of an AXY system, J _AY = 7.6 Hz, J _AX = 1.9 Hz, 1 H, 7-CH of THNaph (= 1,2,3,4-tetrahydronaphthalene)], 7.45 (dd, X part of an AXY system, J _AX = 1.9 Hz, J _XY = 0.6 Hz, 1 H, 5-CH of THNaph), 7.47 (dd, Y part of an AXY system, J _AY = 7.6 Hz, J _XY = 0.6 Hz, 1 H, 8-CH of THNaph). ¹³C NMR (100.6 MHz, CDCl₃): δ = -1.51 (2 C, 2 × SiCH₃), -1.47 (2 C, 2 × SiCH₃), 7.52 (SiCH₂C), 7.55 (SiCH₂C), 19.4 (C-4 of THP), 25.5 (C-5 of THP), 30.6 (C-3 of THP), 62.1 (C-6 of THP), 69.0 (CCH₂O), 97.8 (C-2 of THP), 127.7 (C-7 of THNaph), 132.8 (C-5 of THNaph), 133.6 (C-8 of THNaph), 137.7 (C-6 of THNaph), 144.9, 145.9 (C-8a, C-4a of THNaph). Anal. Calcd for C₁₈H₃₀O₂Si₂: C, 64.61; H, 9.04. Found: C, 64.3; H, 8.7.

<A NAME="RG37906ST-6">6</A>

Synthesis of 5-(Tetrahydropyran-2-yloxymethyl)-1,1,3,3-tetramethyl-1,3-disilaindane ( 3d): Bis(ethynyldimethylsilyl)methane (3.61 g, 20.0 mmol), 2-(prop-2-ynyloxy)tetrahydropyrane (3.93 g, 28.0 mmol), and a solution of cobalt(II) iodide (156 mg, 499 µmol) in MeCN (1.3 mL) were added one after another to a stirred suspension of zinc (131 mg, 2.00 mmol) in MeCN (40 mL). When the reaction mixture started to get warm (after ca. 1 min), it was cooled in an ice-bath. After 5 min the cooling bath was removed, and Et₃N (1 mL) was added. The solvent was removed under reduced pressure, and the residue was purified by column chromatography on silica gel [63-200 µm; eluent: n-pentane-Et₂O, 9:1 ] to give 3d (5.14 g, 80%) as a colorless oil. ¹H NMR (400.1 MHz, CDCl₃): δ = -0.06 (s, 2 H, SiCH₂Si), 0.265 (s, 6 H, 2 × SiCH₃), 0.273 (s, 3 H, SiCH₃), 0.275 (s, 3 H, SiCH₃), 1.47-1.59, 1.80-1.93 (m, 2 H, 4-CH₂ of THP), 1.49-1.66 (m, 2 H, 5-CH₂ of THP), 1.61-1.78 (m, 2 H, 3-CH₂ of THP), 3.50-3.59, 3.89-3.97 (m, 2 H, 6-CH₂ of THP), 4.49, 4.79 (AB system, J _AB = 11.9 Hz, 2 H, CCH₂O), 4.71 (t, J = 3.5 Hz, 1 H, 2-CH of THP), 7.37 (dd, A part of an AXY system, J _AY = 7.4 Hz, J _AX = 1.6 Hz, 1 H, 6-CH of IND), 7.51 (dd, X part of an AXY system, J _AX = 1.6 Hz, J _XY = 0.7 Hz, 1 H, 4-CH of IND), 7.53 (dd, Y part of an AXY system, J _AY = 7.4 Hz, J _XY = 0.7 Hz, 1 H, 7-CH of IND). ¹³C NMR (100.6 MHz, CDCl₃): δ = -2.4 (SiCH₂Si), 0.540 (SiCH₃), 0.546 (SiCH₃), 0.552 (2 C, 2 × SiCH₃), 19.4 (C-4 of THP), 25.5 (C-5 of THP), 30.6 (C-3 of THP), 62.1 (C-6 of THP), 69.2 (CCH₂O), 97.9 (C-2 of THP), 128.4 (C-6 of IND), 131.2 (C-4 of IND), 131.8 (C-7 of IND), 138.3 (C-5 of IND), 149.7, 150.7 (C-3a, C-7a of IND). ²⁹Si NMR (79.5 MHz, CDCl₃): δ = 8.6, 8.8. Anal. Calcd for C₁₇H₂₈O₂Si₂: C, 63.69; H, 8.80. Found: C, 63.3; H, 8.5.

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