4.8. (2S,4R)-2-((Benzyloxy)methyl)-6-methoxy-4-methyl-2-nonyltetrahydro-2H-pyran (23/24)

Dioxane (2R,4S)-22 (0.230 g, 0.547 mmol) and ZrCl₄ (0.013 g, 0.055 mmol) was dissolved in anhydrous methanol (0.6 mL) in a 10 mL microwave vial containing a stirrer bar and stirred under microwave irradiation at 50 °C at 100 W for 6 min. The crude product was purified directly by silica gel column chromatography (pentane/diethyl ether, 9:1) to yield 23 and 24 as an inseparable mixture of colourless oils (0.184 g, 89%). (see Figure S10 for ¹H and ¹³C NMR spectra of compounds 23/24).

Spectroscopic analysis carried out on pure mixture 23/24: R_f = 0.28 (pentane/diethyl ether, 9:1); [α]_D²⁰ = −31.9 (c = 1.0, CHCl₃); IR (neat): ν_max = 2929, 2854, 1454, 1101, 1053 cm⁻¹; ¹H NMR (400 MHz, CDCl₃) δ 7.37–7.21 (m, 5 H), 4.79 (d, J = 3.5 Hz, 1 H), 4.61–4.52 (m, 3 H), 4.49 (dd, J = 9.8, 2.3 Hz, 1 H), 3.48–3.37 (m, 4 H), 3.31–3.22 (m, 1 H), 2.12–1.94 (m, 1 H), 1.93–1.40 (m, 5 H), 1.37–0.80 (m, 25 H) ppm; ¹³C NMR (101 MHz, CDCl₃) δ 138.8, 138.8, 128.4, 128.4, 127.8, 127.6, 127.6, 99.9, 97.9, 77.4, 77.3, 76.5, 76.0, 73.6, 56.0, 55.7, 40.5, 39.9, 39.1, 39.0, 35.3, 32.1, 30.9, 30.6, 30.4, 29.8, 29.8, 29.5, 25.2, 24.6, 22.8, 22.6, 22.3, 19.9, 14.3 ppm; HRMS (ESI-TOF): calcd. for C₂₄H₄₀O₃Na [M + Na]⁺ 399.2875; found 399.2865.