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Synlett 2007(10): 1577-1580  
DOI: 10.1055/s-2007-982556
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Stereoselective Synthesis of the C20-C32 Fragment of the Phorboxazoles

J. S. Yadav*a, M. Satyanarayanaa, G. Srinivasulub, A. C. Kunwarb
a Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500007, India
b Centre for Nuclear Magnetic Resonance, Indian Institute of Chemical Technology, Hyderabad 500007, India
Fax: +91(40)7160387; e-Mail: yadavpub@iict.res.in;
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Publication History

Received 6 October 2006
Publication Date:
06 June 2007 (online)

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Abstract

The C20-C32 fragment of the phorboxazoles was ­realized in a stereoconvergent manner utilizing a desymmetrization approach. This successful strategy involves epimerization and ­modified Julia olefination as key steps.

Keywords

phorboxazole - desymmetrization - epimerization - Julia olefination

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9

The six-membered ring is in the chair form 5C2 conformation. C1-H, C3-H and C5-H have axial orientations confirmed by NOE enhancement between C1-H/C5-H, C1-H/C3-H and C3-H/C5-H and also between C4-Me/C2-H (Figure [1] ). This arrangement is also strongly supported by the coupling constants J C1-H-C2-H = 10.57 Hz, J C3-H-C2-H = 10.57 Hz and J C3-H-C4-H = 4.53 Hz.

Figure 1

15

Spectral Data: Compound 1 [α]D +28.26 (c 0.01, CHCl3); 1H NMR (200 MHz, CDCl3): δ = 0.82 (d, J = 6.07 Hz, 3 H), 0.96 (d, J = 6.96 Hz, 3 H), 1.60-2.16 (m, 4 H) 1.87 (s, 3 H), 2.42 (s, 3 H), 3.24 (dd, J = 5.20, 10.41 Hz, 1 H), 3.44-3.76 (m, 3 H), 4.30-4.68 (m, 5 H), 6.10 (s, 1 H), 7.20-7.34 (m, 10 H), 7.38 (s, 1 H); 13C NMR (50 MHz, CDCl3): δ = 5.80, 13.23, 13.69, 18.72, 33.02, 33,38, 34.44, 67.03, 69.97, 72.95, 74.46, 76.28, 76.92, 77.56, 79.77, 83.99, 119.46, 127.44, 127.62, 128.26, 135.18, 137.24, 138.49, 138.67; LC-MS: m/z = 476 [M + H+].
Compound 10: [α]D +57.29 (c 1.85, CHCl3); 1H NMR (200 MHz, CDCl3): δ = 0.98 (d, J = 7.18 Hz, 3 H), 1.05 (d, J = 7.81 Hz, 3 H), 2.0-2.20 (m, 2 H), 2.25-2.36 (dd, J = 3.9, 15.6 Hz, 1 H), 2.57-2.70 (m, 1 H), 3.30 (s, 3 H), 3.68 (s, 3 H), 3.84 (m, 1 H), 4.25-4.34 (m, 1 H), 4.47-4.50 (m, 3 H), 7.22-7.30 (m, 5 H); 13C NMR (50 MHz, CDCl3): δ = 8.91, 12.89, 35.45, 36.60, 37.31, 51.53, 54.74, 67.34, 69.99, 75.36, 103.42, 127.03, 127.20, 128.14, 172.00; MS (FAB): m/z = 291 [M+- OMe].
Compound 13: colorless oil; [α]D +50.5 (c 1.00, CHCl3); IR (KBr): 3029, 2871, 1743 cm-1; 1H NMR (200 MHz, CDCl3): δ = 1.00 (d, J = 7.23 Hz, 3 H), 1.32 (d, J = 7.23 Hz, 3 H), 1.72-2.12 (m, 2 H), 2.24-2.40 (m, 1 H), 2.72-2.88 (m, 1 H), 3.52-3.72 (m, 2 H), 3.88 (t, J = 5.78 Hz, 1 H), 4.44-4.56 (m, 5 H), 7.24-7.36 (m, 10 H); 13C NMR (50 MHz, CDCl3): δ = 8.64, 12.57, 32.41, 35.56, 39.46, 66.24, 73.19, 73.56, 76.26, 127.44, 127.73, 128.40, 137.78, 138.15, 174.34; MS (FAB): m/z = 369 [M + H+].
Compound 14: colorless oil; [α]D +76.5 (c 1.00, CHCl3); 1H NMR (200 MHz, CDCl3): δ = 0.96 (d, J = 7.55, 3 H), 1.36 (d, J = 6.79 Hz, 3 H), 1.72-1.84 (m, 1 H), 1.96-2.08 (m 1 H), 2.24-2.32 (m, 1 H), 2.44-2.56 (m, 1 H), 3.48 (dd, J = 3.77, 9.82 Hz, 1 H), 3.54-3.60 (m, 2 H), 4.32-4.64 (m, 5 H), 7.24-7.32 (m, 10 H); 13C NMR (75 MHz, CDCl3): δ = 4.72, 14.61, 33.03, 38.31, 65.92, 70.56, 73.17, 76.15, 80.39, 127.61, 128.43, 137.59, 173.54; MS (FAB): m/z = 369 [M + H+].
Compound 16: colorless oil; [α]D +54.54 (c 0.01, CHCl3); IR (KBr): 2961, 2926, 2179 cm-1; 1H NMR (400 MHz, CDCl3): δ = 0.17 (s, 9 H), 0.96 (d, J = 6.79 Hz, 3 H), 1.04 (d, J = 6.79 Hz, 3 H), 1.56-1.68 (m, 1 H), 1.76-2.04 (m, 3 H), 3.09 (dd, J = 4.53, 10.57 Hz, 1 H), 3.46-3.60 (m, 2 H), 3.60-3.64 (d, J = 10.57 Hz, 1 H), 4.10 (q, J = 7.55, 14.35 Hz, 1 H), 4.30 (d, J = 11.33 Hz, 1 H), 4.49 (s, 2 H), 4.59 (d, J = 12.06 Hz, 1 H), 7.20-7.34 (m, 10 H); 13C NMR (50 MHz, CDCl3): δ = 5.99, 14.19, 33.33, 34.47, 37.23, 67.02, 69.96, 73.71, 75.98, 83.05, 103.65, 127.74, 128.44, 138.59; LC-MS: m/z = 450 [M + H+].
Compound 4: colorless oil; [α]D +90.0 (c 0.01, CHCl3); IR (KBr): 2969, 2926, 2858, 1718 cm-1; 1H NMR (400 MHz, CDCl3): δ = 0.84-0.98 (m, 6 H), 1.60-2.20 (m, 4 H), 2.11 (s, 3 H) 3.18 (dd, J = 4.68, 10.93 Hz, 1 H), 3.32 (d, J = 10.93 Hz, 1 H), 3.44-3.64 (m, 3 H), 4.32-4.70 (m, 4 H), 7.28 (m, 10 H); 13C NMR (75 MHz, CDCl3): δ = 6.98, 19.44, 26.51, 27.39, 28.40, 60.78, 64.133, 67.09, 69.16, 70.69, 71.11, 71.53, 77.26, 81.76, 121.69, 121.77, 122.44, 122.45, 132.39, 132.49, 201.15; LC-MS: m/z = 397 [M + H+].
Compound 5: IR (KBr): 3029, 2871, 1743 cm-1; 1H NMR (400 MHz, CDCl3): δ = 2.28 (s, 3 H), 4.71 (s, 2 H), 7.54-7.69 (m, 3 H), 7.99 (m, 1 H), 8.24 (m, 1 H); ESI-MS: m/z 295 [M + H+].