Domino Ring-Closing Metathesis/Intramolecular Transfer of an Alkenyl Subunit: A Direct Formation of Functionalized Butenolides and Pyrones from α,β- and β,γ-Unsaturated Esters

Abstract

A direct synthesis of butenolides and β,γ-unsaturated δ-lactones has been devised by combining a ring-closing metathesis (RCM) with a cross-coupling metathesis (CM) process. The first step of the reaction generates a new carbene group, which is able to functionalize the lateral unsaturated chain during the second coupling reaction. In this way, the transfer of the alkyl group R, initially fixed on the acid chain, avoids the use of an alkene partner introduced in large excess.

Key words

domino reactions - lactones - olefination - ruthenium - ring closure

References

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17

Procedure for the Preparation of Esters 9a and 11c: To a solution of the acid (3 mmol) in CH₂Cl₂ (10 mL) were successively added DMAP (0.122 g, 1 mmol) and 1,4-pentadien-3-ol (0.252 g, 3 mmol). The reaction mixture was cooled to 0 °C and a solution of dicyclohexylcarbodiimide (0.618 g, 3 mmol) in CH₂Cl₂ (1.5 mL) was added dropwise. After stirring for 5 min at 0 °C, the cooling bath was removed and the mixture stirred overnight at r.t. Urea was filtered off and the solvent removed by evaporation under reduced pressure. Purification of the crude product by flash-chromatography on silica (Eluent: EtOAc-hexanes 10:90) afforded the corresponding ester.

18

Spectroscopic data for 9a: ¹H NMR (CDCl₃): δ = 0.89 (t, J = 7.1 Hz, 3 H), 1.23 (m, 4 H), 2.03 (q, J = 6.2 Hz, 2 H), 3.06 (d, J = 5.6 Hz, 2 H), 5.23 (dt, J = 10.4, 1.1 Hz, 2 H), 5.30 (dt, J = 17.1, 1.1 Hz, 2 H), 5.55 (m, 2 H), 5.71 (tt, J = 6.0, 0.9 Hz, 1 H), 5.83 (ddd, J = 17.1, 10.4, 6.0 Hz, 2 H). ¹³C NMR (CDCl₃): δ = 13.6, 21.9, 31.1, 31.9, 37.9, 74.4, 116.8, 121.6, 134.2, 135.1, 169.9 (C=O). HRMS: m/z calcd for [C₁₃H₂₀O₂ + H⁺] = 208.1463. Found: 208.1463. Compound 11c: ¹H NMR (CDCl₃): δ = 0.88 (t, J = 7.0 Hz, 3 H), 1.25-1.52 (m, 8 H), 2.20 (qd, J = 7.0, 1.2 Hz, 2 H), 5.24 (dt, J = 10.4, 1.2 Hz, 2 H), 5.32 (dt, J = 16.9, 1.2 Hz, 2 H), 5.76 (tt, J = 5.9, 1.0 Hz, 1 H), 5.80-5.93 (m, 3 H), 7.00 (dt, J = 15.6, 7.0 Hz, 1 H). ¹³C NMR (CDCl₃): δ = 13.9, 22.4, 27.9, 28.7, 31.5, 32.1, 74.3, 116.9, 121.2, 135.2, 149.4, 164.9 (C=O). HRMS: m/z calcd for [C₁₄H₂₂O₂ +H⁺] = 222.1619. Found: 222.1619. Compound 14: Same procedure as above by using 1,5-hexadien-3-ol (0.288 g, 3 mmol) instead of 1,4-pentadien-3-ol. ¹H NMR (CDCl₃): δ = 0.88 (t, J = 6.6 Hz, 3 H), 1.21-1.50 (m, 8 H), 2.18 (q, J = 7.0 Hz, 2 H), 2.42 (t, J = 6.8 Hz, 2 H), 5.02-5.13 (m, 2 H), 5.18 (dt, J = 10.5, 1.3 Hz, 1 H), 5.26 (dt, J = 17.3, 1.3 Hz, 1 H), 5.37 (q, J = 6.3 Hz, 1 H), 5.68-5.88 (m, 3 H), 6.97 (dt, J = 15.6, 7.0 Hz, 1 H). ¹³C NMR (CDCl₃): δ = 14.0, 22.6, 28.0, 28.9, 31.7, 32.2, 38.9, 73.3, 116.5, 117.8, 121.3, 133.2, 136.1, 149.5, 165.6.

19

Photodeconjugation of ester 11c: To a solution of ester 11c (10 mmol) in CH₂Cl₂ (100 mL) was added N,N-dimethyl-ethanolamine (30 mmol). The resulting solution was first deoxygenated by a stream of nitrogen for 10 min and was then poured into 12 mm diameter quartz tubes which were fitted by septa and placed around a transparent quartz Dewar in which a short wave length OSRAM lamp (λ = 254 nm) was disposed. The irradiation was carried out at 0 °C. After total disappearance of the starting material (thin-layer chromatography control), the solvent was removed by concentration. The deconjugated ester was purified by flash-chromatography (Eluent EtOAc-petrol ether 5:95). Compound 9c: ¹H NMR (CDCl₃): δ = E-isomer: 0.86 (t, J = 6.7 Hz, 3 H), 1.21-1.40 (m, 6 H), 2.04 (q, J = 6.3 Hz, 2 H), 3.06 (d, J = 5.6 Hz, 2 H), 5.23 (d, J = 10.4 Hz, 2 H), 5.30 (dt, J = 17.1, 1.1 Hz, 2 H), 5.56 (m, 2 H), 5.72 (tt, J = 6.0, 1.1 Hz, 1 H), 5.84 (ddd, J = 17.1, 10.4, 6.0 Hz, 2 H). Z-isomer: 0.86 (t, J = 6.7 Hz, 3 H), 1.21-1.40 (m, 6 H), 2.04 (q, J = 6.3 Hz, 2 H), 3.14 (d, J = 5.6 Hz, 2 H), 5.23 (d, J = 10.4 Hz, 2 H), 5.30 (dt, J = 17.1, 1.1 Hz, 2 H), 5.56 (m, 2 H), 5.72 (tt, J = 6.0, 1.1 Hz, 1 H), 5.84 (ddd, J = 17.1, 10.4, 6.0 Hz, 2 H). ¹³C NMR (CDCl₃): δ = E-isomer: 14.2, 22.7, 31.5, 31.7, 32.7, 38.4, 75.1, 117.4, 121.6, 133.7, 135.3, 170.9 (C=O). HRMS: m/z calcd for [C₁₄H₂₂O₂ + H⁺] = 222.1619. Found: 222.1618.

20

Ring-Closing Metathesis/Rearrangement of Esters 9a, 9c, 11c or 14 - General Procedure: To a solution of the ester (1 mmol) in CH₂Cl₂ (100 mL) through which a stream of dried nitrogen had been passed, was added Grubbs type II catalyst (5%). The reaction mixture was heated to reflux for 4 h. After disappearance of the starting material, the reaction mixture was concentrated and purified by flash-chromatography on silica. Compound 6: ¹H NMR (CDCl₃): δ = 3.07 (s, 2 H), 5.25 (dt, J = 10.4, 1.2 Hz, 1 H), 5.34 (dt, J = 17.1, 1.2 Hz, 1 H), 5.41 (m, 1 H), 5.90 (m, 3 H). ¹³C NMR (CDCl₃): δ = 30.3, 80.3, 117.9, 122.4, 125.4, 134.8, 169.8 (C=O). HRMS: m/z calcd for [C₇H₈O₂ + H⁺] = 125.0602. Found: 125.0601. Compound 7a: ¹H NMR (CDCl₃): δ = 0.89 (t, J = 7.0 Hz, 3 H), 1.23-1.48 (m, 4 H), 2.06 (q, J = 6.5 Hz, 2 H), 3.03-3.10 (m, 2 H), 5.33 (s, 1H), 5.49 (ddt, J = 15.3, 7.1, 1.3 Hz, 1 H), 5.79 (dt, J = 15.3, 7.1 Hz, 1 H), 5.86 (s, 2 H). ¹³C NMR (CDCl₃): δ = 14.1, 22.4, 30.2, 31.1, 32.0, 80.6, 121.7, 126.1, 134.2, 136.1, 169.6 (C=O). HRMS: m/z calcd for [C₁₁H₁₆O₂ + H⁺] = 181.1228. Found: 181.1229. Compound 7c: ¹H NMR (CDCl₃): 0.90 (t, J = 6.8 Hz, 3 H), 1.24-1.43 (m, 6 H, H), 2.04 (q, J = 7.2 Hz, 2 H), 3.03-3.10 (m, 2 H), 5.31-5.39 (m, 1 H), 5.48 (ddt, J = 15.3, 7.2, 1.3 Hz, 1 H), 5.79 (dt, J = 15.3, 7.2 Hz, 1 H), 5.86 (s, 2 H). ¹³C NMR (CDCl₃): δ = 14.3, 22.8, 28.7, 30.3, 31.6, 32.3, 80.6, 121.9, 126.2, 126.7, 136.0, 169.2 (C=O). HRMS: m/z calcd for [C₁₂H₁₈O₂ + H⁺] = 265.2167. Found: 265.2166. Compound 12a:^{21 1}H NMR (CDCl₃): δ = 5.35 (d, J = 10.2 Hz, 1 H), 5.43 (s, 1 H), 5.48 (d, J = 17.0 Hz, 1 H), 5.72 (ddd, J = 17.0, 10.2, 6.9 Hz, 1 H), 6.17 (dd, J = 5.6, 2.1 Hz, 1 H), 7.43 (dd, J = 5.7, 1.4 Hz, 1 H). ¹³C NMR (CDCl₃): δ = 84.0, 120.1, 121.6, 131.6, 155.3, 173.2 (C=O). 13c:^{22 1}H NMR (CDCl₃): δ = 0.90 (t, J = 6.7 Hz, 3 H), 1.23-1.40 (m, 8 H, H), 2.06 (q, J = 6.6 Hz, 2 H), 5.25 (ddt, J = 15.3, 7.7, 1.2 Hz, 1 H), 5.39 (d, J = 7.7 Hz, 1 H), 5.90 (dt, J = 15.3, 6.9 Hz, 1 H), 6.09 (dd, J = 5.6, 1.9 Hz, 1 H), 7.35 (dd, J = 5.6, 1.5 Hz, 1 H). ¹³C NMR (CDCl₃): δ = 14.2, 22.7, 28.8, 28.9, 31.8, 32.4, 84.2, 121.4, 123.3, 138.3, 155.8, 173.3 (C=O). HRMS: m/z calcd for [C₁₂H₁₈O₂ + H⁺] = 194.1307. Found: 194.1308. Compound 17: ¹H NMR (CDCl₃): δ = 0.87 (t, J = 6.6 Hz, 3 H), 1.21-1.39 (m, 8 H), 2.02 (q, J = 6.7 Hz, 2 H), 2.36-2.60 (m, 2 H), 5.04 (t, J = 6.4 Hz, 1 H), 5.37 (dt, J = 15.3, 7.7 Hz, 1 H), 5.60 (dt, J = 15.3, 7.5 Hz, 1 H), 6.13 (dd, J = 5.7, 2.1 Hz, 1 H), 7.46 (dd, J = 5.7, 1.4 Hz, 1 H). ¹³C NMR (CDCl₃): δ = 14.4, 22.9, 29.1, 29.5, 32.0, 32.9, 36.6, 83.3, 122.2, 122.3, 136.5, 156.3, 173.3 (C=O). HRMS: m/z calcd for [C₁₃H₂₀O₂ + H⁺] = 208.1463. Found: 208.1462. Compound 8: ¹H NMR (CDCl₃): δ = 0.88 (t, J = 6.7 Hz, 3 H), 1.20-1.40 (m, 8 H), 1.86-2.10 (m, 2 H), 2.32-2.54 (m, 2 H), 4.86 (q, J = 7.0 Hz, 1 H), 5.57 (dt, J = 15.1, 7.0 Hz, 1 H), 5.81 (dt, J = 15.1, 6.7 Hz, 1 H), 6.02 (dt, J = 9.8, 1.9 Hz, 1 H), 6.84 (dt, J = 9.8, 4.2 Hz, 1 H).