References and Notes
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Typical Procedure for Tandem Deoxygenation-Rearrangement-Electrophile Trapping: Xanthate (+)-3 (250 mg, 0.71 mmol) was dissolved in toluene (20 mL) and then heated to reflux. (Me3Si)3SiH (256 mg, 1.1 mmol), AIBN (58 mg, 0.36 mmol) and methyl acrylate (9.6 µL, 1.1 mmol)
were dissolved in toluene (4 mL) and were added to the refluxing solution via syringe
pump over 100 min. The reaction mixture was allowed to reflux for a further 30 min
before being cooled to r.t. and evaporated under reduced pressure. Column chromatography
[SiO2; gradient elution 5% → 20% Et2O in PE (bp 30-40 °C)] of the residue gave ester (+)-10 as a colourless oil (131 mg, 56%); R
f
(Et2O-PE, 1:4) 0.07; [α]D
25 81.0 (c = 1.00, CHCl3). IR (neat): 2977 (m), 1739 (s), 1695 (s), 1462 (m), 1366 (s), 1260 (m), 1170 (s),
1121 (m), 1100 (m), 1074 (m), 1000 (w), 910 (w), 839 (w), 757 (m) cm-1. 1H NMR (400 MHz, CDCl3): δ = 7.05-7.39 (m, 4 H, aromatic CH), 4.86, 4.98 (0.25 H, 0.75 H, rotamers, CH),
3.67 (s, 3 H, OCH3), 2.92-3.04, 2.79-2.92 (m, 0.75 H, 0.25 H, rotamers CH), 2.59-2.44 (m, 2 H, CH2), 2.08-2.30 (overlapping m, 2 H, 2 × CH), 1.79-1.98 (m, 1 H, CH2), 1.71-1.79 (m, 1 H, CH2), 1.35-1.42, 1.26-1.35 [m, 10 H, C(CH3)3, CH]. 13C NMR (100 MHz, CDCl3): δ = 174 (CO), 157 (CO), 146 (quat. aromatic), 144 (quat. aromatic), 127 (aromatic
CH), 126 (aromatic CH), 122, 121 (rotamers, aromatic CH), 120 (aromatic CH), 79.5
[C(CH3)3], 62.7, 61.7 (rotamers, CH), 59.8 (CH), 51.8, 51.5 (rotamers, CH3), 48.2, 47.8 (rotamers, CH), 45.3, 44.8 (rotamers, CH2), 32.5, 31.9 (rotamers, CH2), 30.5, 30.3 (rotamers, CH2), 28.5, 28.3 [rotamers, C(CH3)3]. MS (CI+): m/z (%) = 332 (100) [M + H]+, 276 (43), 232 (77), 214 (12), 200(5), 183 (4), 172 (10), 158 (15), 144 (17), 130
(11), 116 (26). HRMS: m/z calcd for C19H26NO4: 332.1865; found: 332.1866.
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This is consistent with the observation that increasing the equivalents of the alkene
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1625 ) to the corresponding (+)-ketone (79%) allowed determination by chiral HPLC:
Chiralcel OD column (4.6 × 250 mm); flow rate: 0.2 mL/min; eluted with 1% EtOH in
heptane; t
R
(major) = 112 min, t
R (minor, not observed in the enantioenriched product) = 139 min
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Determined by chiral GC analysis: Chirasil Dex-CD column; flow rate: 1.0 mL/min; t
R (minor, not observed in the enantioenriched product) = 540 min, t
R(major) = 544 min.
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