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

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

References and Notes

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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.