Download PDF
Synlett 2008(20): 3111-3114  
DOI: 10.1055/s-0028-1087275
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Aromatics to Diquinanes: An Expeditious Synthesis of Tetramethyl­bicyclo[3.3.0]octane Framework of Ptychanolide

Vishwakarma Singh*a, Girish Chandraa, Shaikh M. Mobinb
a Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
Fax: +91(22)25723480; e-Mail: vks@chem.iitb.ac.in;
b National Single-Crystal X-ray Diffraction Facility, Indian Institute of Technology Bombay, Mumbai 400076, India
Further Information

Publication History

Received 9 August 2008
Publication Date:
26 November 2008 (online)

    Permissions and Reprints All articles of this category

Abstract

An expeditious route to methyl-7-oxo-1,4,5,8-tetra­methylbicyclo[3.3.0]octane-3-carboxylate from a simple aromatic precursor is described. Oxidative dearomatization of 2-hydroxy­methyl-3,4,6-trimethylphenol into spiroepoxycyclohexa-2,4-dienone, its cycloaddition and triplet-sensitized 1,2-acyl shift, and stereochemical inversion are the key features of our methodology.

Key words

cycloaddition - oxa-di-π-methane rearrangement - diquinanes - Diels-Alder reaction

12

All the compounds gave satisfactory spectral data.
Data of Compound 6
IR (neat): 1735 (br) cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 5.55 (br s, 1 H), 3.68 (s, 3 H), 3.06 (part of an AB system, J = 5.86 Hz, 1 H), 2.92 (part of an AB system, J = 5.86 Hz, 1 H), 2.77 (dd, J 1 = 10.26 Hz, J 2 = 5.87 Hz, 1 H), 2.15 (dd, J 1 = 13.19 Hz, J 2 = 10.26 Hz, 1 H), 1.87 (d, J = 1.46 Hz, 3 H), 1.74 (dd, J 1 = 12.83 Hz, J 2 = 5.87 Hz, 1 H), 1.26 (s, 3 H), 1.04 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 204.3, 173.8, 146.2, 124.9, 59.1, 51.9, 50.6, 49.6, 45.2, 40.9, 36.7, 17.9, 15.7, 14.4. ESI-HRMS: m/z calcd for C14H19O4: 251.1283 [M + H]+; found: 251.1277 [M + H]+.

17

Data of Compound 14
IR (neat): 1735 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 3.68 (s, 3 H), 2.44-2.36 (m, 1 H), 2.32-2.15 (m, 2 H), 2.01 (d of AB pattern, J = 19.42 Hz, 1 H), 1.92 (d of AB pattern, J = 19.42 Hz, 1 H), 1.76-1.62 (m, 2 H), 1.09 (s, 3 H), 1.04-0.98 (m, 9 H). ¹³C NMR (100 MHz, CDCl3): δ = 219.0, 176.6, 53.2, 52.0, 50.7, 48.1, 45.6, 45.1, 36.4, 23.5, 21.4, 20.7, 14.2, 8.8. ESI-HRMS: m/z calcd for C14H23O3: 239.1647 [M + H]+; found: 239.1655 [M + H]+.

18

Data for Hydrazone Derivative 15 IR (neat): 1731 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 10.82 (br s, 1 H), 9.13 (d, J = 2.44 Hz, 1 H), 8.30 (dd, J 1 = 8.85 Hz, J 2 = 1.83 Hz, 1 H), 7.97 (d, J = 9.47 Hz, 1 H), 3.69 (s, 3 H), 2.67-2.45 (m, 1 H), 2.41-2.31 (m, 1 H), 2.30-2.25 (m, 2 H), 2.10 (d, J = 18.32 Hz, 1 H), 1.74-1.62 (m, 2 H), 1.19 (d, J = 6.72 Hz, 3 H), 1.10-1.09 (m, 6 H), 1.03 (s, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 176.6, 167.7, 145.2, 137.8, 130.1, 129.0, 123.7, 116.5, 53.4, 53.4, 52.0, 48.3, 47.9, 45.7, 35.8, 35.4, 20.9, 20.8, 14.3, 11.1. ESI-HRMS: m/z calcd for C20H27O6N4: 419.1931 [M + H]+; found: 419.1939 [M + H]+.
Crystal Data of Hydrazone Derivative 15
C20H26N4O6, M 418.45, space group, monoclinic, P 21/c, a = 20.475 (4), b = 14.245 (2), c = 7.3712 (12) Å, α = 90, β = 99.326 (19), γ = 90.0, U = 2121.5 (6)A³, Z = 4, D c  = 1.310 g/m³, T = 150 (2) K, F(000) = 888, size = 0.21 × 0.18 × 0.15 mm. Reflections/collected/unique 10087/3694 [R(int) = 0.1809], final R indices [I > 2σ(I)] = R 1 =  = 0.0732, wR 2 = 0.1210 R indices (all data) R 1 = 0.2346, wR 2 = 0.1622. The complete crystal data can be obtained free of charge from The Cambridge Crystallographic data Centre via www.ccdc.cam.ac.uk/data_request/cif quoting the CCDC number 694681.

19

Data of Compound 18 IR (neat): 1736 (br) cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 3.70 (s, 3 H), 2.58-2.50 (dd with structure, J 1 = 18 Hz, J 2 = 9 Hz, 1 H), 2.41-2.34 (d with structure, J = 9 Hz, 1 H), 2.24-2.16 (m, 2 H), 2.00-1.86 (m, 3 H), 1.03 (d, partly merged with a s, J = 7.33 Hz, 3 H), 1.02 (s, 3 H), 1.00 (s, 3 H), 0.99 (d, partly merged with s, J = 6.72 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 220.3, 176.3, 53.2, 51.9, 50.9, 50.6, 49.0, 47.3, 46.1, 44.2, 23.7, 18.9, 15.2, 11.9. ESI-HRMS: m/z calcd for C14H23O3: 239.1647 [M + H]+; found: 239.1655 [M + H]+.