Synthesis 2007(10): 1584-1586  
DOI: 10.1055/s-2007-965954
PSP
© Georg Thieme Verlag Stuttgart · New York

Simple and Efficient Preparation of Reagents for Thiopyran Introduction:
Methyl Tetrahydro-4-oxo-2H-thiopyran-3-carboxylate, Tetrahydro-4H-thiopyran-4-one, and 3,6-Dihydro-4-trimethylsilyloxy-2H-thiopyran

Dale E. Ward*, M. Abdul Rasheed, H. Martin Gillis, Garrison E. Beye, Vishal Jheengut, George T. Achonduh
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK, S7N 5C9, Canada
Fax: +1(306)9664730; e-Mail: dale.ward@usask.ca;
Further Information

Publication History

Received 4 October 2006
Publication Date:
28 February 2007 (online)

Abstract

Tetrahydro-4H-thiopyran-4-one was prepared in >75% yield by treatment of dimethyl 3,3′-thiobispropanoate with NaOMe (generated in situ) in THF solution and decarboxylation of the resulting methyl tetrahydro-4-oxo-2H-thiopyran-3-carboxylate in refluxing 10% aqueous H2SO4. Reaction of tetrahydro-4H-thiopyran-4-one with Me3SiCl and Et3N in CHCl3 gave the corresponding trimethylsilyl enol ether in near quantitative yield. The prepared reagents are useful for the synthesis of thiopyran-containing compounds.

12

A reaction using 1.1 equiv of NaOMe did not go to completion within 5 h (ca. 90% conversion).

15

Na metal was cut into pieces weighing ca. 50-100 mg (3-5 mm per side). The rate of Na consumption depends on the size of pieces; with larger pieces, more time is required to reach 90% conversion.

16

A few specks of Na metal may remain at this point.

17

The presence of small amounts of 1 (<1%) and its corresponding half-acid (1-2%) were detected by 13C NMR and confirmed by spiking with authentic samples.