Gold(I)-Catalyzed Formation of 5-Methylene-1,3-oxazolidin-2-ones

Abstract

A study concerning the gold(I)-catalyzed rearrangement of propargylic tert-butylcarbamates into 5-methylene-1,3-oxazolidin-2-ones is described. The mild reaction conditions employed allow the efficient synthesis of a variety of these structures, which would be less conveniently obtained using other reported methods.

Key words

gold catalysis - ring closure - oxazolidinones

References and Notes

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• 12 These substrates substituted at the propargylic position (5i-n) were synthesized according to the method developed by Petrini and coworkers. See, for instance: Mecozzi T. Petrini M. J. Org. Chem.  1999,  64:  8970 

9

The work recently reported by Carretero and coworkers (see ref. 8) was only dealing with the synthesis of oxazolidinones substituted at the nitrogen and alkyne terminus.

10

Ozaxolidinone 6a could, however, be synthesized in 94% yield (3 h, CH₂Cl₂, r.t.) when the more electrophilic (p-CF₃Ph)₃PAuNTf₂ catalyst (1 mol%) was used instead of PPh₃AuNTf_2.

11

Representative Experimental Procedure - Synthesis of 3-Benzyl-4,4-dimethyl-1,3-oxazolidin-2-one (6d).
To a solution of benzyl (1,1-dimethylprop-2-ynyl)carbamic acid tert-butyl ester (5d, 136 mg, 0.5 mmol) in 1 mL of CH₂Cl₂ was added PPh₃AuNTf₂ (3.7 mg, 0.005 mmol). The reaction mixture was stirred for 5 min, then filtered through a small pad of silica and the solvent was removed under reduced pressure. The residue was then purified by flash column chromatography (PE-EtOAc, 60:40) to give oxazolidinone 6d (108 mg, 99%, pale yellow solid); mp 69-70 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.39-7.27 (m, 5 H), 4.68 (d, J = 3.3 Hz, 1 H), 4.48 (s, 2 H), 4.25 (d, J = 3.3 Hz, 1 H), 1.33 (s, 6 H). ¹³C NMR (50 MHz, CDCl₃): δ = 160.7, 154.8, 137.6, 128.6, 127.8, 127.7, 84.1, 61.5, 44.0, 27.6. IR (CCl₄): 2979, 1786, 1692, 1663, 1393, 1054 cm^-1. MS (CI + NH₃): m/z = 235 [MNH₄ ⁺], 218 [MH⁺]. HRMS (EI): m/z calcd for C₁₃H₁₅O₂N: 217.1103; found: 217.1103.