CpRuCl(PPh₃)₂/MeI Catalyst System for the [2+2] Cycloaddition of Norbornenes with Disubstituted Alkynes

Abstract

CpRu(PPh₃)₂I generated in situ by mixing CpRu(PPh₃)₂Cl and methyl iodide catalyzed the [2+2] cycloaddition of norbornene (or norbornadiene) and disubtituted alkynes to afford functionalized cyclobutenes.

Key words

ruthenium catalyst - cycloaddition - alkynes - bicyclic alkenes - cyclobutenes

References

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11

Tenaglia, A.; Giordano, L. submitted for publication.

14

The structure of CpRuI(PPh₃)₂ was secured by an X-ray analysis and deposited with the Cambridge Crystallographic Data Centre (CCDC 219110). The coordinates can be obtained, on request, from the Director, Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2, 1EZ, UK.

17

Typical Procedure: A solution of CpRuCl(PPh₃)₂ (36.3 mg, 0.05 mmol) and methyl iodide (49.6 mg, 22 µL, 0.35 mmol) in dioxane (2 mL) was stirred for 10 min in a Schlenk tube under an Ar atmosphere. A solution of norbornene 1 (282 mg, 3 mmol) and alkyne (1 mmol) in dioxane (6 mL) was added and the mixture was heated at 90 °C until completion (TLC monitoring). Dioxane was evaporated in vacuo and the crude product was purified by SiO₂ column chromato-graphy.

18

All new compounds exhibited satisfactory ¹H and ¹³C NMR and IR spectral data as well as satisfactory combustion analysis. The following physical data are representative:
Tricyclo[4.2.1.0 [2] [5] ]non-3-ene-3,4-diyldimethanol 4a. White solid, R_f = 0.73 (CH₂Cl₂/MeOH 9/1). Mp 57-58 °C. IR (KBr): 3307, 2946, 1665 cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 1.01 (m, 3 H), 1.51 (m, 3 H), 1.96 (m, 2 H), 2.31 (br s, 2 H), 2.84 (m, 2 H, OH), 4.11 (br s, 4 H). ¹³C NMR (50 MHz, CDCl₃): δ = 28.1 (t), 30.3 (t), 33.6 (d), 46.3 (d), 58.7 (t), 140.2 (s). Anal. Calcd for C₁₁H₁₆O₂: C, 73.30; H, 8.95. Found: C, 73.12; H, 8.84.
Tricyclo[4.2.1.0 [2] [5] ]nona-3,7-diene-3,4-diyldimethanol 5a. White solid, R_f = 0.70 (CH₂Cl₂/MeOH 9/1). Mp 59-60 °C. IR (KBr): 3293, 3056, 2966, 1654 cm^-1. ¹H NMR (200 MHz, CDCl₃): δ = 1.31 (br d, J = 9.0 Hz, 1 H), 1.43 (br d, J = 9.0 Hz, 1 H), 2.18 (br s, 2 H), 2.43 (br s, 2 H), 3.68 (m, 2 H, OH), 4.20 (br s, 4 H), 6.10 (t, J = 1.6 Hz, 2 H). ¹³C NMR (50 MHz, CDCl₃): δ = 38.2 (d), 39.6 (t), 42.6 (d), 59.1 (t), 135.4 (d), 140.2 (s). Anal. Calcd for C₁₁H₁₄O₂: C, 74.13; H, 7.92. Found: C, 73.93; H, 7.78.