Cationic Palladium Complex-Catalyzed Cyclization-Hydrosilylation of 1,6-Heptadiyne and its Homologs

Abstract

Palladium complex (A)-catalyzed dimerization-hydro-silylation of 1-alkynes, which has previously been reported, can not be applied effectively to the intramolecular version of α,ω-alkanediynes, while a cationic palladium complex (B) is a very effective catalyst for cyclization-hydrosilylation of functionalized α,ω-diynes to give (Z)-1-methylene-2-silylmethylenecycloalkane derivatives, with 5-, 6-, and 7-membered ring, in good to moderate yields.

cyclization - hydrosilylation - cationic palladium complex - α,ω-diyne - 5-, 6-, and 7-membered carbocycle

References

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7

Typical procedure for the cyclization-hydrosilylation of 1 with HSiCl₃ is as follows: In a 10 mL screw-capped glass tube were placed, under an argon atmosphere, 1 (0.208 g, 1.0 mmol), the catalyst precursor B (2.0 mg, 5 × 10^-3 mmol, 0.5 mol%), and HSiCl₃ (2 M CH₂Cl₂ solution 0.55 mL, 1.1 mmol) diluted with dry CH₂Cl₂ (0.45 mL). The orange-yellow clear solution was magnetically stirred for 24 h at r.t. GLC (10% Silicone SE-30 on uniport B, 3 mm × 3 m column, programmed 100˜280 °C) analysis of the reaction mixture revealed recovered 1 (ca.4%) and the product peaks (96%) in a ratio 8:92 (T _R = 16.8 and 17.7 min). The whole mixture was treated with dry EtOH (0.20 mL, 3.3 mmol) and Et₃N (0.46 mL, 3.3 mmol) dissolved in CH₂Cl₂ (6 mL) for 2 h in an ice-water bath. The turbid solution formed was filtered through a celite plug, the latter being rinsed with dry hexane, and the combined filtrate was thoroughly concentrated by rotary evaporation. The crude products (0.332 g, ca. 89%), in a ratio 8:92 (T _R = 18.2 and 19.3 min), was subjected to a bulb-to-bulb distillation (150-170 °C/3 Torr) to give pure 2b as a colorless liquid (0.207 g, 56% yield), the probable (E)-isomer being hard to be detected within an accuracy of NMR spectra.

8

Spectral data for 2b: ¹H NMR (270 MHz, CDCl₃):
δ (ppm) = 1.21 (t, J = 6.9 Hz, 1 H), 3.08 (br t, J = 2.2 Hz,
2 H), 3.13 (br d, J = 1.7 Hz, 2 H), 3.72 (s, 6 H), 3.80 (q, J = 6.9 Hz, 6 H), 5.17 (br t, J = 2.2 Hz, 1 H), 5.32 (br t, J = 2.0 Hz, 1 H), 5.95 (t, J = 2.3 Hz, 1 H). ¹³C NMR (67.8 MHz): δ (ppm) = 18.1 (× 3), 42.1, 45.1, 52.8, 56.9, 58.4 (× 3), 112.0, 112.5, 143.7, 158.3, 171.6.

9

Spectral data for 4b: ¹H NMR: δ = 1.20 (t, J = 6.9 Hz, 9 H), 1.85 (s, 3 H), 3.00 (t, J = 1.7 Hz, 2 H), 3.07 (d, J = 1.3 Hz, 2 H), 3.75 (s, 6 H), 3.77 (q, J = 6.9 Hz, 6 H), 5.04 (s, 1 H), 5.73 (s, 1 H). ¹³C NMR: δ = 18.1 (× 3), 20.0, 40.4, 42.7, 52.8, 56.4, 58.3 (× 3), 111.1, 122.0, 144.3, 151.8, and 171.9.

10

Spectral data for (Z)-6′b: ¹H NMR: δ = 1.23 (t, J = 6.9 Hz, 9 H), 1.82 (br s, 3 H), 3.82 (q, J = 6.9 Hz, 6 H), 4.47 (t, J = 2.0 Hz, 2 H), 4.55 (d, J = 1.3 Hz, 2 H), 5.09 (d, J = 0.66 Hz, 1 H), 5.96 (t, J = 2.0 Hz, 1 H). ¹³C NMR: δ = 18.1 (× 3), 19.7, 58.5 (× 3), 73.4, 74.5, 108.0, 120.9, 143.1, 150.9. The stereochemistry was determined by NOE experiments (NOE, Figure [1] ).
It was found that pure (Z)-6′b, dissolved in degassed CDCl₃ in a sealed NMR tube, isomerized significantly to (E)-6′b in months: Z/E = 30/70. (E)-6′b: ¹H NMR: δ = 1.24 (t, J = 6.9 Hz, 9 H), 2.05 (t, J = 2.0 Hz, 3 H), 3.83 (q, J = 6.9 Hz, 6 H), 4.43 (t, J = 2.0 Hz, 2 H), 4.60 (q, J = 2.0 Hz, 2 H), 5.27 (t, J = 2.0 Hz, 1 H), 5.45 (br s, 1 H).

11

Spectral data for (Z)-10b (estimated 84%): ¹H NMR: δ = 1.22 (t, J = 6.9 Hz, 9 H), 1.67 (m, 4 H), 2.27 (m, 2 H), 2.33 (m, 2 H), 3.79 (q, 6.9 Hz, 6 H), 4.80 (d, J = 1.3 Hz, 1 H), 5.00 (d, J = 1.5 Hz, 1 H), 5.07 (d, J = 1.7 Hz, 1 H). ¹³C NMR: δ = 18.2 (× 3), 27.5, 27.7, 36.6, 41.1, 58.3 (× 3), 110.5 112.1, 149.4, 164 8. (E)-10b (estimated 16%): ¹H NMR: δ = 1.19 (t, J = 6.9 Hz, 9 H), 3.78 (q, J = 6.9 Hz, 6 H), 4.78 (br s, 1 H), 5.02 (br s, 1 H), 5.11 (d, J = 2.3 Hz, 1 H). Other signals are overlapped with those of Z-isomer. ¹³C NMR (diagnostic signals): δ = 110.7, 113.4, 149.3, 163.8.

12

Spectral data for 12b: ¹H NMR: δ = 1.21 (t, J = 6.9 Hz, 9 H), 1.59 (br s, 6 H), 2.34 (m, 2 H), 2.42 (m, 2 H), 3.78 (q, J = 6.9 Hz, 6 H), 4.87 (dt, J = 2.0, 1.3 Hz, 1 H), 5.07 (t, J = 1.3 Hz, 1 H), 5.18 (d, J = 2.0 Hz, 1 H). ¹³C NMR: δ = 18.21 (× 3), 28.7, 29.4, 30.9, 35.5, 40.4, 49.7, 58.3 (× 3), 113.4, 114.6, 151.9, 167.7.

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17

Spectral data for an adduct of 2c with N-methylmaleimide: ¹H NMR: δ = 0.13 (s, Me), 1.21 and 1.22 (t, J = 6.9 Hz, diastereotopic Me), 2.37 (br s, 1 H), 2.46 (br s, 2 H), 2.84-3.24 (m, 6 H), 2.95 (s, 3 H), 3.69 and 3.71 (s, 2 × Me), 3.78 and 3.79 (q, J = 6.9 Hz, diastereotopic methylene). ¹³C NMR: δ = -5.80, 18.35, 24.31, 25.28, 26.00, 39.28, 39.55, 43.56, 44.01, 52.71, 52.76, 57.68, 58.58 and 58.65 (diastereotopic methylene), 128.25, 131.68, 172.20, 172.51, 180.59, 180.79.