Synthesis of Novel Phenylnaphthyl Phosphines and their Applications to Pd-Catalyzed Intramolecular Amidation

Abstract

Novel phenylnaphthyl phosphines were prepared and ­applied to the Pd-catalyzed intramolecular amidation. Both ligands gave good to excellent yields in the synthesis of five-, six-, and ­seven-membered rings from halo-amides and carbamates.

Key words

phenylnaphthyl phosphine - Pd catalysis - C-N bond formation - intramolecular amidation - Suzuki-Miyaura cross-coupling

References and Notes

• For reviews on transition-metal catalyzed carbon-heteroatom bond formations, see:
• 1a Prim D. Andrioletti B. Rose-Munch F. Rose E. Couty F. Tetrahedron  2004,  60:  3325 
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• Our group has used the structurally related optically active 8,8′-disubstituted 1,1′-binaphthyls as chiral modifiers. For examples, see:
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9

The ligand 6 could be purified by column chromatography under atmospheric conditions. Spectral data of 6: ¹H NMR: δ = 3.37 (s, 3 H), 6.67-6.65 (m, 1 H), 6.86 (dd, J = 0.8, 7.0 Hz, 1 H), 7.16-7.11 (m, 5 H), 7.27-7.21 (m, 9 H), 7.37-7.31 (m, 2 H), 7.74-7.44 (m, 1 H), 7.74 (dd, J = 0.8, 8.0 Hz, 1 H). MS (FAB): m/z = 419 (M + H)⁺. HRMS: m/z calcd for C₂₉H₂₄OP (M + H)⁺, 419.1564; found, 419.1531.

11

Spectral data of 11: ¹H NMR: δ = 3.48 (s, 3 H), 6.65-6.60 (m, 1 H), 6.83-6.70 (m, 4 H), 7.30-7.00 (m, 13 H), 7.50-7.45 (m, 1 H), 7.88 (d, J = 7.9 Hz, 2 H). MS (FAB): m/z = 419 (M + H)⁺. HRMS: m/z calcd for C₂₉H₂₄OP (M + H)⁺, 419.1564; found, 419.1524.

13

Intramolecular Amidations; General Procedure To a mixture of 6 (9.8 mg, 23 µmol) and Pd(OAc)₂ (6.3 mg, 28 µmol) in 1,4-dioxane (3.0 mL) was added 12 (142 mg, 0.47 mmol) and Cs₂CO₃ (228 mg, 0.70 mmol) at r.t. The reaction was stirred at 100 °C for 3.5 h, EtOAc and H₂O were added, and the resulting mixture was filtered through a pad of Celite. The organic layer was separated, washed with brine, dried over MgSO₄, and then evaporated to give a residue, which was purified by column chromatography (SiO₂; hexane-EtOAc, 3:2) to afford 13 (88 mg, 85%).

14

In a previous report, the cyclization of 12 was conducted with Pd(OAc)₂ (3.3 mol%), (dl)-MOP (5.0 mol%), and K₂CO₃ (1.4 equiv) in toluene at 100 °C for 36 h to give 13 in 82%; see, ref. 12a.

16

The starting material 12 was recovered in 72% yield. No reductive dehalogenation of 12 as a side reaction was observed.

18

Attempts to synthesize the eight-, nine-, and ten-membered lactams using 23, 24, and 25 as the starting materials, respectively, were unsuccessful (Figure [2] ).
In every case only the starting materials were recovered.