Mercuric Triflate·3TMU Catalyzed Cyclization of ω-Alkynoic Acids and ­Synthesis of a Naturally Occurring γ-Methylene-γ-lactone

Abstract

Hg(OTf)₂·3TMU showed efficient catalytic activity for the cyclization of ω-alkynoic acid to give ω-methylene-ω-lactone in excellent yield, and the procedure was efficiently applied for the synthesis of naturally occurring γ-methylene-γ-lactone. The absolute structure of the natural product was established by this synthesis.

catalytic cyclizations - carboxylic acids - alkynes - lactones - mercury

References and Notes

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We could obtain neither the natural product nor NMR spectra and could not check the purity of the natural product.

19

General Experimental Procedure.
To a solution of alkynoic acid (0.30 mmol) in CD₃CN (3 mL, 0.1 M) was added tetramethylurea (0.1 M in CD₃CN, 90 µL, 9.0 µmol) and then a 0.1 M CD₃CN solution of Hg(OTf)₂ (30 µL, 3.0 µmol) at r.t. After stirring for 15 min at r.t., Et₃N (100 µL, 0.14 mmol) and naphthalene (internal standard, 0.3 M CD₃CN solution, 0.25 mL, 0.075 mmol) were added. The solution was directly subjected to ¹H NMR analysis, and the yield was calculated from the integral value.