4.10. (4R,6S)-6-((Benzyloxy)methyl)-4-methyl-6-nonyltetrahydro-2H-pyran-2-one (25)

Acetals 23/24 (0.164 g, 0.436 mmol) were dissolved in CH₂Cl₂ (13 mL) in a dry 50 mL Schlenk tube containing a magnetic stirrer bar and cooled to 0 °C. m-CPBA (0.113 g, <77%, 0.653 mmol) was added followed by BF₃·OEt₂ (0.070 mL, 0.566 mmol) and the reaction mixture was stirred at room temperature for 30 min. The reaction mixture was cooled back to 0 °C, quenched slowly with Et₃N (0.30 mL, 2.18 mmol) and stirred for 30 min. Excess solvent removed in vacuo. The crude product residue was purified by silica gel column chromatography (pentane/diethyl ether, 4:1) to yield 25 as a colourless oil (0.066 g, 42%). (see Figure S12 for ¹H and ¹³C NMR spectra).

Spectroscopic analysis of 25: R_f = 0.36 (pentane/diethyl ether, 3:2); [α]_D²⁰ = −7.0 (c = 0.9, CHCl₃); IR (neat): ν_max = 2929, 2856, 1720, 1454, 1215, 1099 cm⁻¹; ¹H NMR (400 MHz, CDCl₃) δ 7.44–7.22 (m, 5 H), 4.62 (d, J = 12.1 Hz, 1 H), 4.54 (d, J = 12.1 Hz, 1 H), 3.46 (s, 2 H), 2.62–2.51 (m, 1 H), 2.16–1.97 (m, 2 H), 1.81 (dd, J = 13.6, 3.5 Hz, 1 H), 1.74–1.54 (m, 3H), 1.48–1.17 (m, 14 H), 1.04 (d, J = 6.0 Hz, 3 H), 0.90 (t, J = 6.7 Hz, 3 H) ppm; ¹³C NMR (101 MHz, CDCl₃) δ 171.8, 138.0, 128.4, 127.6, 127.6, 85.1, 75.2, 73.6, 38.2, 37.6, 36.3, 31.8, 30.0, 29.5, 29.4, 29.2, 24.0, 23.3, 22.6, 21.2, 14.1 ppm; HRMS (ESI-TOF): calcd. for C₂₃H₃₆O₃Na [M + Na]⁺ 383.2562; 383.2574.