Palladium/TBADT-Cocatalyzed Acyl C–H Alkenylation of Aldehydes with Alkenyl Triflates

Abstract

By merging palladium and tetrabutylammonium decatungstate as a hydrogen-atom-transfer photocatalyst, we accomplished the acyl C–H alkenylation of aldehydes with alkenyl triflates, enabling the synthesis of a variety of multi-substituted cyclic alkenes under mild conditions.

Key words

α,β-unsaturated ketones - alkenylation - acylation - palladium - hydrogen-atom transfer

Publication History

Received: 13 February 2025

Accepted after revision: 10 March 2025

Accepted Manuscript online:
10 March 2025

Article published online:
14 April 2025

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• 11 Ethyl 2-Butyrylcyclohex-1-ene-1-carboxylate (3aa); Typical Procedure: Pd(TFA)₂ (3.3 mg, 0.01 mmol, 5 mol%), tri-o-tolylphosphane (L4; 6.1 mg, 0.02 mmol, 10 mol%), tetrabutylammonium decatungstate (TBADT; 33.2 mg, 0.01 mmol, 5 mol%), and K₃PO₄ (46.6 mg, 0.22 mmol, 1.1 equiv) were placed in a Schlenk tube equipped with a stir bar. After the Schlenk tube was evacuated and filled with nitrogen (three cycles), MeCN (1.0 mL), ethyl 2-{[(trifluoromethyl)sulfonyl]oxy}cyclohex-1-ene-1-carboxylate (1a; 0.2 mmol, 1.0 equiv), and butyraldehyde (2a; 43.2 mg, 0.6 mmol, 3.0 equiv) were added under a positive flow of nitrogen. The resultant mixture was stirred and irradiated using two 34 W 390 nm LED lamps (Kessil PR160-390, 5 cm away, with adequate fans to maintain the reaction at room temperature) for 18 h. After exposure to air for 15 min, the crude materials were purified through column chromatography on silica gel (petroleum ether/ethyl acetate = 20:1) to give the product 3aa (34.1 mg, 76% yield). ¹H NMR (500 MHz, CDCl₃): δ = 4.17 (q, J = 7.1 Hz, 2 H), 2.57–2.52 (m, 2 H), 2.41–2.05 (m, 4 H), 1.72–1.64 (m, 6 H), 1.26 (t, J = 7.1 Hz, 3 H), 0.96 (t, J = 7.4 Hz, 3 H). ¹³C NMR (126 MHz, CDCl₃): δ = 208.6, 167.0, 150.9, 126.5, 60.9, 43.1, 27.7, 24.7, 21.5, 21.3, 16.9, 14.1, 13.8. HRMS (ESI): m/z calcd. for C₁₃H₂₀NaO₃ ⁺: 247.1305; found: 247.1311.