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DOI: 10.1055/a-1928-7408
Stereoselective Synthesis of Acyclic Skeleton of Boscartin A
D.S, M.H.S, and G.H.M thank the Indian Association for the Cultivation of Science and the Council of Scientific and Industrial Research (CSIR), India, New Delhi for their research fellowship. The financial support from Science and Engineering Research Board (project no. CRG/2019/001664), Department of Science and Technology (DST), Ministry of Science and Technology, India to carry out this work is gratefully acknowledged.
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Abstract
Stereoselective synthesis of key acyclic skeleton of structurally challenging and biologically active boscartin A possessing six stereogenic centers, among which three are tertiary, has been achieved for the first time. The synthetic study comprises the Sharpless asymmetric epoxidation (SAE) followed by stereoselective epoxide opening for installation of C-11 and C-12 centers, Meyer–Schuster rearrangement followed by intramolecular oxa-Michael addition for construction of C-1 center, SAE followed by CBS reduction and subsequent cycloetherification for stereoselective generation of C-3, C-4, and C-7 centers, Gilman reaction for introduction of C-9 olefin and Grignard reaction for installation of C-8 olefin.
Supporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/a-1928-7408.
- Supporting Information
Publication History
Received: 21 July 2022
Accepted after revision: 22 August 2022
Accepted Manuscript online:
22 August 2022
Article published online:
21 September 2022
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- 14 General Experimental Procedure All moisture-sensitive reactions were performed in oven- or flame-dried glassware with Teflon-coated magnetic stirring bar under argon atmosphere using dry, freshly distilled solvents. Air- and moisture-sensitive liquids were transferred via a gastight syringe and a stainless-steel needle. Reactions were monitored by thin-layer chromatography (TLC, silica gel 60 F254) plates with UV light, ethanolic anisaldehyde (with 1% AcOH and 3.3% concd H2SO4), heat, and aqueous KMnO4 (with K2CO3 and 10% aqueous NaOH solution) as developing agents. All workup and purification procedures were carried out with reagent-grade solvents under ambient atmosphere unless otherwise stated. Column chromatography was performed using silica gel 60–120 mesh, 100–200 mesh, and 230–400 mesh. Yields mentioned as chromatographically and spectroscopically homogeneous materials unless otherwise stated. Optical rotations were measured only for pure compounds and not for mixtures using sodium (589, D line; Anton Paar MCP 200 system) lamp and are reported as follows: [α]D 25 (c = g/100 mL, solvent). IR spectra were recorded as neat (for liquids). HRMS were taken using Quadruple-TOF (Q-TOF) micro-MS system using electrospray ionization (ESI) technique. NMR spectra were recorded on 300, 400, 500, and 600 MHz and 13C and 2D NMR spectra were recorded on 75 and 150 MHz spectrometers in appropriate solvents and the chemical shifts are shown in ppm scales. 3-[(2R,3R)-3-{[(2S,5R)-5-{(S)-2-(Benzyloxy)-1-[(tert-butyldimethylsilyl)oxy]ethyl}-2-isopropyl-5-methyltetrahydrofuran-2-yl]methyl}-2-methyloxiran-2-yl]propan-1-ol (12) Colorless liquid; yield 80%. Rf = 0.35 (20% EtOAc/hexane); [α]D 25 +12.6 (c 0.4, CHCl3). 1H NMR (300 MHz, CDCl3): δ = 7.37–7.27 (m, 5 H), 4.50 (s, 2 H), 3.88 (dd, J = 9.5, 1.4 Hz, 1 H), 3.71 (dd, J = 7.7, 1.4 Hz, 1 H), 3.58–3.52 (m, 1 H), 3.39 (dd, J = 9.5, 7.7 Hz, 1 H), 2.95 (dd, J = 6.2, 4.9 Hz, 1 H), 2.05–1.87 (m, 4 H), 1.83–1.69 (m, 5 H), 1.61–1.53 (m, 2 H), 1.25 (s, 3 H), 1.11 (s, 3 H), 0.91 (d, J = 6.8 Hz, 3 H), 0.87 (s, 12 H), 0.07 (s, 6 H). 13C NMR (75 MHz, CDCl3): δ = 138.7, 128.3, 127.6, 127.4, 88.0, 84.8, 78.5, 73.8, 73.3, 62.5, 60.7, 60.3, 37.5, 37.0, 34.9, 33.9, 32.3, 27.8, 26.1, 21.6, 18.3, 17.7, 16.9, –3.6, –5.0 ppm. IR (neat): νmax = 3447, 2956, 2857, 1471, 1250. 1095, 834 cm–1. HRMS (ESI): m/z calcd for C30H52NaO5Si [M + Na]+: 543.3482; found: 543.3484. (S)-1-[(2R,5S)-5-{(R)-2-hydroxy-2-[(2S,5R)-2-methyl-5-(prop-1-en-2-yl)tetrahydrofuran-2-yl]ethyl}-5-isopropyl-2-methyltetrahydrofuran-2-yl]but-3-en-1-ol (10) Colorless liquid; yield 79%. Rf = 0.5 (20% EtOAc/hexane); [α]D 25 – 5.7 (c 0.2, CHCl3). 1H NMR (300 MHz, CDCl3): δ = 5.96 (ddt, J = 17.0, 10.1, 6.8 Hz, 1 H), 5.17–5.02 (m, 2 H), 4.99 (s, 1 H), 4.79 (s, 1 H), 4.30 (dd, J = 9.9, 5.7 Hz, 1 H), 3.93 (d, J = 9.5 Hz, 1 H), 3.66 (dd, J = 9.9, 2.7 Hz, 1 H), 2.36–2.09 (m, 5 H), 2.01 (ddd, J = 17.2, 7.7, 3.4 Hz, 3 H), 1.84–1.72 (m, 2 H), 1.71 (s, 3 H), 1.44 (dt, J = 12.4, 6.6 Hz, 3 H), 1.16 (s, 3 H), 1.14 (s, 3 H), 1.01 (d, J = 6.7 Hz, 3 H), 0.86 (d, J = 7.0 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ = 145.8, 136.6, 116.3, 110.5, 88.7, 87.8, 85.9, 84.0, 75.3, 72.7, 37.2, 37.0, 32.2, 31.8, 31.4, 30.7, 29.0, 24.4, 23.4, 18.9, 18.0, 17.5 ppm. IR (neat): νmax = 3470, 2975, 2936, 1472, 1153, 973 cm–1. HRMS (ESI): m/z calcd for C22H38NaO4 [M + Na]+: 389.2668; found: 389.2665.