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Synlett 2003(12): 1797-1800  
DOI: 10.1055/s-2003-41466
LETTER
© Georg Thieme Verlag Stuttgart · New York

Atom Transfer Radical Cyclisations Mediated by the Grubbs Ruthenium Metathesis Catalyst

Peter Quayle*a, David Fengasa, Stuart Richardsb
a Department of Chemistry, University of Manchester, Manchester M13 9PL, UK
Fax: +44(161)2754939; e-Mail: peter.quayle@man.ac.uk;
b Zeneca Specialties, Blackley, Manchester, UK
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Publication History

Received 16 July 2003
Publication Date:
19 September 2003 (online)

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Abstract

The commercially available ruthenium carbene complex RuCl2(=CHPh)(PCy3)2 efficiently catalyses the cyclisation of halo alkenes to γ-lactones and γ-lactams.

Keywords

carbene complexes - free radicals - metathesis - lactones - lactams

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Cyclisation of Ester 10 to Lactone 11 Using Catalyst 3 is Representative: A dry flask was charged with the Grubbs catalyst 3 (169.7 mg, 5 mol%, Strem) and toluene (5 mL). The contents of the flask were degassed (three times using freeze-thaw cycle) to which was added, by syringe, a solution of the trichloroacetate 10 (1.0 g, 4.12 mmol) in toluene (3 mL). After degassing (three times, freeze-thaw cycle) the reaction mixture was brought to a gentle reflux under argon for 3.5 h. The toluene was removed under reduced pressure and the crude product chromatographed (‘flash’ silica, eluent: 10% EtOAc-petroleum ether) to afford the lactone 11 as a white solid (mp 56-58 °C) in 75% yield. 1H NMR (300 MHz, CDCl3) δ: 2.2 (2 H, m, CH2), 2.4 (2 H, m, CH2), 2.95 (1 H, dt, J = 13, 4.4 Hz), 5.1 (1 H, t, J = 4.4 Hz), 6.0 (1 H, m, olefin), 6.3 (1 H, m, olefin). 13C NMR (75 MHz, CDCl3) δ: 167.1, 136.2, 121.0, 82.9, 60.3, 50.44, 23.8, 21.7. IR (cm-1, CHCl3): 1793, 1755. m/e (CI) 224 (100%) (M + NH4)+, 190 (45%). HRMS: C8H8O2 35Cl2, calcd: 205.9901; found: 205.9901.

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The cyclisation of 1 was reported by Nagashima [9] to be highly diastereoselective although a stereochemical assignment was not made.

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Trichloroacetamides were prepared from the respective sulfonamides by acylation with trichloroacetylchloride. The following procedures are representative:
Synthesis of sulfonamide 23 (Scheme [4] ).
To a solution of camphorsulfonyl chloride (13.2 g, 52.69 mmol) in dichloromethane (20 mL) was added a mixture of triethylamine (7.32 mL, 1 equiv) and allylamine (3.9 mL, 2 equiv) in anhydrous dichloroethane (20 mL). The reaction mixture was left at r.t. for 3 h and then poured into Et2O and partitioned with 1 M HCl (100 mL). The organic layer was separated, dried (MgSO4) and concentrated in vacuo to afford the sulfonamide 19 in 90% yield as a yellow solid (mp 50-51 °C). This material was sufficiently pure to be used directly in the next step. 1H NMR (300 MHz, CDCl3) δ (ppm): 0.95 (3 H, s, Me), 1.05 (3 H, s, Me), 2.0-2.4 (7 H, m), 2.95 (1 H, d, J = 15.1 Hz, CH2SO), 3.4 (1 H, d, J = 15.1 Hz, CH2SO), 3.85 (2 H, m, CH2CH=CH2), 5.25 (2 H, m, CH=CH2), 5.95 (1 H, m, CH=CH2). 13C NMR (75 MHz, CDCl3) δ (ppm): 216.9, 133.6, 117.6, 59.1, 50.2, 50.2, 48.7, 46.1, 46.0, 42.8, 26.9, 26.6, 19.8, 19.4. IR (cm-1, CHCl3): 3290, 2960, 1741. m/e (CI) 289 [(M + NH4)+, 100%], 272 (100%), 215 (80%). HRMS: C13H22O3SN, (M + H)+ calcd: 272.1320; found: 272.1320. The sulfonamide 19 (2.0 g, 7.38 mmol) was dissolved in methanol (20 mL) to which was added sodium borohydride (0.3 g, 1.0 equiv) and the resulting solution left to stir at 0 °C until all the starting material had been consumed (TLC). The reaction mixture was concentrated in vacuo and partitioned between water (150 mL) and Et2O (5 × 50 mL). The organic extracts were dried (MgSO4), concentrated in vacuo and the residue chromatographed (‘flash’ silica; eluent: 20% EtOAc-petroleum ether) to afford the alcohol 22 as a viscous oil (95% yield). 1H NMR (300 MHz, CDCl3) δ (ppm): 0.8 (3 H, s, Me), 1.0 (3 H, s, Me), 1.4-1.8 (7 H, m), 2.9 (1 H, d, J = 13.7 Hz, CH2SO), 3.16 (1 H, d, J = 8.7 Hz, OH), 3.4 (1 H, d, J = 13.7 Hz, CH2SO), 3.85 (2 H, t, J = 6.0 Hz, CH2CH=CH2), 4.1 (1 H, dd, J = 4.1, 7.7 Hz, CH-OH), 4.4 (1 H, bt, J = 6.0 Hz, NH), 5.2 (2 H, m, CH=CH2), 5.8 (1 H, m, CH=CH2). 13C NMR (75 MHz, CDCl3) δ (ppm): 133.6, 117.9, 80.5, 52.9, 50, 40.8, 45.7, 44.3, 38.9, 30.4, 27.2, 20.4, 19.7. IR (cm-1, CHCl3): 3515, 3285, 2953. m/e (CI): 291 [(M + NH4)+, 30%], 256 (100%). HRMS: C13H23O3SN, (M+H)+ calcd: 274.1477; found: 274.1477. To a solution of the sulfonamide 22 (1.6 g; 5.86 mmol) in anhydrous THF (15 mL) at -78 °C was added n-BuLi (4.4 mL, 1.2 equiv, 1.6 M solution in hexanes). After 30 min at -78 °C trichloroacetylchloride (0.72 mL, 1.1 equiv) was added and the reaction mixture left to stir at this temperature for period of two hours. On warming up to 0 °C the reaction was quenched with saturated ammonium chloride solution (50 mL) and extracted with Et2O (3 × 50 mL). The organic extracts were dried (MgSO4), concentrated in vacuo and the residue chromatographed (‘flash’ silica; eluent: 20% EtOAc-petroleum ether) to afford the sulfonamide 26 as a viscous colourless oil (90% yield). 1H NMR (300 MHz, CDCl3) δ (ppm): 0.9 (3 H, s, Me), 1.05 (3 H, s, Me), 1.4-1.8 (7 H, m), 3.4 (1 H, d, J = 13.2 Hz, CH2SO), 3.95 (1 H, d, J = 13.2 Hz, CH2SO), 4.2 (1 H, dd, J = 4.1, 7.6 Hz, CH-OH), 4.8 (2 H, m, CH2-CH=CH2), 5.45 (2 H, m, CH=CH2), 6.0 (1 H, m, CH=CH2). 13C NMR (75 MHz, CDCl3) δ (ppm): 163.6, 131.5, 120.5, 90.0, 76.3, 55.3, 50.9, 50.6, 49.2, 44.3, 38.9, 30, 27.2, 20.5, 19.7. IR (cm-1, CHCl3): 3568, 2955, 1760, 1707. m/e (CI): 435 [(M + NH4)+, 70%], 234 (35%), 108 (100%). HRMS: C15H22O4SN35Cl3 calcd: 417.0335; found: 417.0335.

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Catalyst loadings of 30 mol% are not untypical for such reactions, especially for the cyclisation of esters to lactones, as noted in ref. [14]