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Synlett 2008(18): 2823-2825  
DOI: 10.1055/s-0028-1083536
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Convenient Formal Synthesis of (+)-Grandisol through Lewis Acid Promoted Enantioselective Pinacolic Rearrangement

Angelo Frongiaa, Christian Girardb, Jean Ollivierb, Pier Paolo Piras*a, Francesco Seccia,b
a Dipartimento di Scienze Chimiche, Università di Cagliari, Complesso Universitario di Monserrato, S.S. 554, Bivio per Sestu, 09042 Monserrato, Cagliari, Italy
Fax: +39(070)6754388; e-Mail: pppiras@unica.it;
b Laboratoire de Synthèse Organique et Méthodologie, UMR 8182, Institut de Chimie Moléculaire et des Matériaux d’Orsay, Université de Paris-Sud XI, 91405 Orsay, France
Fax: +33(1)69157252; e-Mail: jollivie@icmo.u-psud.fr;
Further Information

Publication History

Received 23 June 2008
Publication Date:
15 October 2008 (online)

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Abstract

The titanium-mediated cyclopropanation of an easily prepared chiral a-siloxylactone leads efficiently to an enantiomerically pure cyclopropanol derivative. The trimethylsilyl trifluoro­methane sulfonate induced pinacol rearrangement allows high level of chirality transfer into a cyclobutanone, which is a useful intermediate in the total synthesis of (+)-grandisol.

Key words

antifugal agents - aldol reactions - rearrangements - ring expansion - ketones

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Reduction Procedure: To a solution of [(4S)-4-methyl-5-oxo-2-(tribromomethyl)-1,3-dioxolan-4-yl]acetic acid (4; 2.64 g, 6.45 mmol) in anhyd THF (15 mL) was added dropwise at -10 ˚C under argon a solution of borane methyl sulfide complex (1.75 mL, 3.48 mmol, 2 M in THF). After stirring for an additional hour at -10 ˚C, the reaction mixture was allowed to warm overnight to r.t. The mixture was quenched with MeOH (1 mL) and concentrated under reduced pressure and the resulting oil was diluted in Et2O (50 mL). The ethereal phase was washed with brine (5 mL) and then dried over Na2SO4. After evaporation of the solvent, the residue was purified by flash chromatography to afford pure (3S)-dihydro-3-hydroxy-3-methyl-2(3H)-furanone (5; 0.65 g, 83%); [α]D ²0 -32.2 (c 0.1, CHCl3).

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Crystallographic data for (-)-9: C13H28O3Si, M = 260.44, monoclinic, space group C2, a = 12.359(5) Å, b = 7.468(5) Å, c = 17.642(5) Å, β = 101.69˚, Z = 2, V = 1594.54 ų. Full crystallographic data have been deposited with the Cambridge Crystallographic Data Centre CCDC as supplementary publication number CCDC 697709. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge, CB2 IEZ, UK, fax:
+44 (1223)336033, e-mail: deposit@ccdc.cam.ac.uk; www.ccdc.cam.ac.uk/data_request/cif.

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Selected data:
1-[(1 S )-1-( tert -Butyldimethylsilyloxy)-3-hydroxy-1-methylpropyl]cyclopropanol (9): colorless needles; mp
65 ˚C; [α]D ²0 -12 (c 0.1, CHCl3). IR (KBr): 3289, 2957, 1464, 1254 cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 3.94-4.03 (m, 1 H), 3.64-3.78 (m, 1 H), 2.02-2.07 (m, 1 H), 1.70-1.87 (m, 1 H), 1.31 (s, 3 H), 0.82-0.97 (m, 2 H), 0.84 (s, 9 H), 0.59-0.64 (m, 2 H), 0.11 (s, 3 H), 0.07 (s, 3 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 75.3, 60.1, 58.3, 43.0, 41.9, 25.2, 11.4, 8.2, 2.6, 2.3. HRMS (ES, +): m/z calcd for C13H28O3SiNa: 283.17054; found: 283.17058.
1-[(1 S )-3-(Benzyloxy)-1-( tert -butyldimethylsilyloxy)-1-methylpropyl]cyclopropanol (12): colorless oil; [α]D ²0 -34 (c 0.05, CHCl3). IR (neat): 3501, 2929, 1454, 1256 cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 7.29-7.37 (m, 5 H), 4.54 (Abq, J = 3.3 Hz, 2 H), 3.96-4.03 (m, 1 H), 3.71-3.78 (m,
1 H), 3.69 (s, 1 H), 1.99-2.15 (m, 1 H), 1.89-1.97 (m, 1 H), 1.27 (s, 3 H), 0.76-0.93 (m, 2 H), 0.87 (s, 9 H), 0.59-0.63 (m, 2 H), 0.10 (s, 3 H), 0.06 (s, 3 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 129.2, 128.4, 128.2, 126.9, 78.2, 58.6, 40.0, 37.3, 29.2, 26.2, 25.6, 9.4, 7.5, 2.8, 2.3. HRMS (ES, +): m/z calcd for C19H34O3SiNa: 373.21749; found: 373.21712. (2 R )-2-(2-Benzyloxyethyl)-2-methylcyclobutanone (2): colorless oil; [α]D ²4 +42 (c 0.1, CHCl3). IR (neat): 1765
cm-¹. ¹H NMR (300 MHz, CDCl3): δ = 7.30 (m, 5 H), 4.43 (Abq, J = 11.7 Hz, 2 H), 3.56 (t, J = 6.3 Hz, 2 H), 2.98 (t, J = 6.3 Hz, 2 H), 1.93-2.01 (m, 2 H), 1.86 (s, 3 H), 1.64-1.79 (m, 2 H). ¹³C NMR (62.9 MHz, CDCl3): δ = 214.8, 138.1, 128.2, 127.4, 127.3, 72.8, 66.7, 62.2, 42.3, 35.3, 23.9, 21.3. MS (EI): m/z (%) = 218 (1) [M+], 127 (12), 97 (11), 91 (100), 41 (38).