Download PDF
Synlett 2007(14): 2189-2192  
DOI: 10.1055/s-2007-984915
LETTER
© Georg Thieme Verlag Stuttgart · New York

The Chemistry of α,β-Ditosyloxyketones: Novel Routes for the Synthesis of Desoxybenzoins and α-Aryl-β-ketoaldehyde Dimethylacetals from α,β-Chalcone Ditosylates

Om Prakash*, Rajesh Kumar, Deepak Sharma, Kamaljeet Pannu, Raj Kamal
Department of Chemistry, Kurukshetra University, Kurukshetra, Haryana 136119, India
Fax: +91(1744)238277; e-Mail: dromprakash50@rediffmail.com;
Further Information

Publication History

Received 16 May 2007
Publication Date:
20 July 2007 (online)

    Permissions and Reprints All articles of this category

Abstract

The reaction of α,b-chalcone ditosylates 3 with potassium hydroxide in suitable conditions leads to 1,2-aryl shift and carbon-carbon bond cleavage, thereby providing a novel route for the synthesis of 1,2-diarylethan-1-ones 4 and 1,2-diaryl-3,3-dimethoxy propan-1-ones 5.

Key words

α,β-ditosyloxyketones - desoxybenzoins - α,β-chalcone ditosylates

6

Experimental Procedure for α,β-Chalcone Ditosylates 3: To a solution of chalcone (1b, 1.11 g, 0.005 mol) in CH2Cl2 (40 mL) was added HTIB (3.92 g, 0.01 mol). The resulting mixture was allowed to stir at 40-42 °C. HTIB was highly insoluble in CH2Cl2, but gradually disappeared as the reaction proceeded. The stirring was allowed to continue for about 16-18 h. The solvent was evaporated in vacuo. The gummy mass so obtained was triturated with PE (60-80 °C) to remove iodobenzene. The colorless solid obtained was thoroughly washed with H2O to remove p-toluenesulfonic acid formed as byproduct. The solid was recrystallized from MeCN to give the pure chalcone ditosylate 3b; yield: 1.66 g (59%); mp 114-115 °C. IR (KBr): 1675 (CO stretch) cm-1. 1H NMR (300 MHz, CDCl3): δ = 2.21 (s, 3 H, Me), 2.43 (s, 6 H, Me), 5.00 (d, J = 8.1 Hz, 1 H, CH), 6.97 (d, J = 8.1 Hz, 1 H, CH), 6.80-6.87 (m, 2 H, ArH), 7.10-7.21 (m, 4 H, ArH), 7.32-7.35 (m, 3 H, ArH), 7.38-7.48 (m, 4 H, ArH), 7.71-7.79 (m, 4 H, ArH). Anal. Calcd for C30H28O7S2: C, 63.8; H, 4.9. Found: C, 62.7; H, 4.2.
Other derivatives 3a, 3c-3j were prepared in a similar manner.

7

Experimental Procedure for Desoxybenzoins 4: To a solution of α,β-chalcone ditosylate 3a (0.550 g, 0.01 mol) in EtOH (20 mL) was added KOH (0.112 g, 0.02 mol). The mixture was heated under reflux for 2-3 h. The progress of the reaction was monitored by TLC. When all of the starting material had been consumed, the reaction mixture was poured over crushed ice, extracted with CH2Cl2 and the crude product 4a was purified by column chromatography using EtOAc-PE as eluent; yield: 0.114 g (58%); mp 52-54 °C (Lit. mp 55-56 °C). IR (KBr): 1685 (CO stretch) cm-1. 1H NMR (300 MHz, CDCl3): δ = 4.18 (s, 2 H, CH2), 7.12-7.13 (m, 2 H, ArH), 7.51-7.70 (m, 6 H, ArH), 7.99-8.21 (m, 2 H, ArH).
Other derivatives 4b-j were prepared in a similar manner.

17

Experimental Procedure for α-Aryl-β-ketoaldehyde Dimethylacetals 5: To a solution of α,β-chalcone ditosylate 3a (0.550 g, 0.01 mol) in EtOH (20 mL) was added KOH in catalytic amount. The mixture was stirred at r.t. for about 2 h and was heated under reflux for 2-3 h. The reaction mixture was poured over crushed ice. The crude product 5a was purified by recrystallization using MeOH as a solvent; yield: 0.138 g (51%); mp 93-94 °C (Lit.18 mp 94.5-96.5 °C). IR (KBr): 1682 (CO stretch) cm-1. 1H NMR (300 MHz, CDCl3): δ = 3.28 (s, 3 H, OMe), 3.49 (s, 3 H, OMe), 4.92 (d, J = 9.0 Hz, 1 H, CH), 5.16 (d, J = 9.0 Hz, 1 H, CH), 7.04-7.05 (m, 2 H, ArH), 7.39-7.68 (m, 6 H, ArH), 7.97-8.08 (m, 2 H, ArH).
Other derivatives 5b-5j were prepared in a similar manner.