Palladium-Catalyzed Regioselective Allylic Alkylation of 1-Aryl-2,3,3-trifluoroallyl Acetates

Abstract

The palladium-catalyzed allylic alkylation of 1-aryl-2,3,3-trifluoroallyl acetates, which possess fluorinated olefinic parts, has been demonstrated; the reaction was effectively conducted by using P(t-Bu)₃ or XANTPHOS as a ligand, and the reaction proceeded with a high regioselectivity.

fluorine - palladium catalyst - regioselectivity - allylic alkylation - phosphine ligand

References and Notes

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6

Typical Procedure for the Reaction of 1-Phenyl-2,3,3-trifluoroallyl Acetate (3A) with Diethyl Methylmalonate (6a, Entry 4) To a solution of [PdCl(π-C₃H₅)]₂ (18.3 mg, 0.050 mmol) and XANTPHOS (57.9 mg, 0.100 mmol) in toluene (5 mL) was added 2,3,3-trifluoro-1-phenylallyl acetate (230 mg, 1.00 mmol). A solution of sodium salt of diethyl methylmalonate prepared from diethyl methylmalonate (261 mg, 1.50 mmol) and NaH (33.6 mg, 1.40 mmol) in THF (1.5 mL) was added dropwise at 0 °C, and the resultant mixture was heated up to 60 °C and stirred for 12 h. Then, Et₂O and H₂O were added to the reaction mixture, and the organic phase was separated, and dried over MgSO₄ and evaporated. The regioselectivity was determined from the ¹H NMR spectrum of the crude materials, then determined to be 99:1. Analytically pure samples were obtained by silica gel column chromatog-raphy (hexane-Et₂O, 98:2) to give 306 mg (89%) of alkylation product 4Aa. ¹H NMR (500 MHz, CDCl₃): δ = 1.13 (t, J = 7.1 Hz, 3 H), 1.27 (t, J = 7.3 Hz, 3 H), 1.58 (d, J _HF = 1.8 Hz, 3 H), 3.99-4.09 (m, 2 H), 4.23 (qd, J = 7.1 Hz, J _HF = 0.9 Hz, 2 H), 4.60 (ddd, J _HF = 35.5, 3.0, 1.6 Hz, 1 H), 7.27-7.38 (5 H, m). ¹³C NMR (125 MHz, CDCl₃): δ = 13.8, 13.9, 18.4, 45.4 (ddd, J _CF = 17.3, 4.8, 1.9 Hz), 57.6, 61.7, 61.9, 128.0, 128.4, 129.1 (ddd, J _CF = 240.9, 48.9, 17.3 Hz), 129.8, 135.4, 153.1 (ddd, J _CF = 47.1, 287.9, 277.3 Hz), 169.9, 170.4. ¹⁹F NMR (470 MHz, CDCl₃): δ = -13.5 (ddd, J _FF = 109.4, 34.5 Hz, J _FH = 34.5 Hz), 44.2 (dd, J _FF = 109.4, 74.5 Hz), 58.0 (dd, J _FF = 34.5, 74.5 Hz).

7 Williams reported the reaction of methyl-substituted allyl acetate 1 and 2 (R = Me) gave branch selectivity by using P(t-Bu)₃, however, we confirmed the reaction of 1-phenyl-2-propenyl acetate 1 (R = Ph) gave 60% branch selectivity: Acemoglu L. Williams JMJ. Adv. Synth. Catal.  2001,  343:  75 

8 Kranenburg M. van der Burgt YEM. Kamer PCJ. van Leeuwen PWNM. Goubitz K. Fraanje J. Organometallics  1995,  14:  3018 

9

XANTPHOS [9,9-dimethyl-4,5-bis(diphenylphos-phino)xanthene] gave 92% linear selectivity for the reaction of 1-phenyl-2-propenyl acetate 1 (R = Ph).