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Synlett 2005(14): 2167-2170  
DOI: 10.1055/s-2005-872258
LETTER
© Georg Thieme Verlag Stuttgart · New York

The Synthesis of Arylketones via Friedel-Crafts Acyldegermylation

Alan C. Spivey*a, Christopher J. G. Griptonb, Catherine Nobana, Nigel J. Parrc
a Department of Chemistry, Imperial College, South Kensington Campus, London, SW7 2AZ, UK
e-Mail: a.c.spivey@imperial.ac.uk;
b Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, S3 7HF, UK
c Medicinal Chemistry, GlaxoSmithKline, Gunnelswood Road, Stevenage, Hertfordshire, SG1 2NY, UK
Further Information

Publication History

Received 17 June 2005
Publication Date:
03 August 2005 (online)

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Abstract

Electron-rich and electron-neutral aryl trialkylgermanes are shown to be competent precursors to aryl ketones via Friedel-Crafts acyldegermylation. Given the previously demonstrated greater stability towards basic/nucleophilic conditions of arylgermanes as compared to arylsilanes/stannanes, these reactions significantly expand the utility of group 14 acyldemetalation in synthesis. This is exemplified by the cleavage of Ge-based linker models for solid-phase synthesis (SPS).

Key words

arylgermanes - solid-phase synthesis - electrophilic aromatic substitution - Friedel-Crafts acylation - oligothiophenes

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    (f) Compound 2i: a clear colourless oil, R f = 0.79 (PE-EtOAc, 8:2). 1H NMR (250 MHz, CDCl3): δ = 0.46 [9 H, s, (CH 3)3Ge], 1.44 (3 H, t, J = 7.0 Hz, CH2CH 3), 4.43 (2 H, q, J = 7.0 Hz, CH 2CH3), 7.42-7.48 (1 H, m, GeCCHCHCHCCO2Et), 7.67-7.71 (1 H, m, GeCCHCHCHCCO2Et), 8.02-8.07 (1 H, m, GeCCHCHCHCCO2Et), 8.21 (1 H, m, GeCCHCCO2Et). 13C NMR (63 MHz, CDCl3): δ = -1.8 (q), 14.4 (q), 60.8 (t), 127.8 (d), 129.4 (d), 129.9 (s), 133.9 (d), 137.4 (d), 143.0 (s), 166.9 (s). IR (neat): 2977, 2908, 1715, 1590, 1367, 1261, 1117, 826, 742 cm-1. MS (EI): m/z (%) = 268 (1) [M+], 253 (100), 225 (48), 149 (17), 119 (31), 104 (28), 91 (34), 89 (32). HRMS (ESI+): m/z calcd for C12H19 74GeO2: 269.0597; found: 269.0588.
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    Compound 10: a clear colourless oil, R f = 0.38 (PE-EtOAc, 9:1). 1H NMR (400 MHz, CDCl3): δ = 0.41 [9 H, s, Ge(CH 3)3], 2.58 (3 H, s, COCH 3), 3.88 (3 H, s, OCH 3), 6.89 (1 H, dd, J = 8.5, 3.0 Hz, CH3OCCHCHCCOCH3), 7.21 [1 H, d, J = 3.0 Hz, (CH3)3GeCCH], 7.91 (1 H, d, J = 8.5 Hz, CH3COCCH). 13C NMR (63 MHz, CDCl3): δ = 0.0 (q), 26.8 (q), 55.1 (q), 111.9 (d), 121.2 (d), 132.5 (d), 143.3 (s), 167.2 (s), two quaternary carbons not observed. IR (neat): 2964, 1677, 1587, 1563, 1269, 1227, 1045, 827 cm-1. MS (EI): m/z (%) = 253 (100) [M - Me]+, 238 (11), 223 (27), 119 (23), 89 (18). HRMS (EI): m/z calcd for C12H18 74GeO2: 268.0519; found: 268.0521.
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    Compound 18: as colourless blocks, R f = 0.54 (PE-EtOAc, 9:1); mp 29-31 °C. 1H NMR (270 MHz, CDCl3): δ = 0.086 (3 H, t, J = 7.0 Hz, CH 3CH2), 1.29-1.35 (6 H, m, CH 2 CH 2 CH 2 CH3), 1.53-1.58 (2 H, m, CCH2CH 2 ), 2.45 (3 H, s, COCH 3), 2.92 (2 H, t, J = 8.0 Hz, CCH 2CH3), 7.13 (1 H, s, CH). 13C NMR (125 MHz, CDCl3): δ = 14.1 (q), 22.6 (t), 29.2 (t), 29.8 (t), 30.2 (2 × t), 31.6 (t), 81.1 (s), 141.5 (d), 141.7 (s), 151.6 (s), 189.4 (s). IR (neat): 2955, 2855, 1653, 1401, 1237, 954 cm-1. MS (CI+): m/z (%) = 337 (100) [M + H], 354 (51), 279 (9), 228 (17), 211 (23). HRMS (CI+): m/z calcd for C12H18OSI: 337.0123; found: 337.0120.
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16

Subjection of 2-TMG-4-methoxyacetophenone 12 to aluminium(III) chloride/AcCl to see if a second acyl group could be installed by ipso-degermylation resulted in the formation of no identifiable products.