Straightforward Synthesis of Strained α,β-Epoxysulfones via Epoxidation of Vinylsulfones Using N-Methylmorpholine N-Oxide as Epoxidizing Reagent

Abstract

An efficient, stereoselective route to the α,β-epoxy­sulfones using N-methylmorpholine N-oxide (NMO) as epoxidizing reagent is described.

Key words

vinylsulfone - α,β-epoxysulfone - N-methylmorpholine N-oxide - epoxidation

References and Notes

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• 12 Four isolated cases regarding the epoxidation reaction of α,β-unsaturated esters 16 with an amine oxide (NMO) to give endo-epoxides 17 (Scheme 4) have been previously described. See: Andres CJ. Spetseris N. Norton JR. Meyers AJ. Tetrahedron Lett.  1995,  36:  1613 
• Compounds 4 and 5 were synthesized by cycloaddition reaction of p-toluenesulfonylacetylene with furan and N-Boc pyrrole, respectively:
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• 13d

  In the same fashion, cycloaddition of cyclopentadiene and p-toluenesulfonylacetylene gave 6 in 99% isolated yield. Compound 7 (30% isolated yield) was prepared by trapping of isobenzofuran 22 [generated by reaction of 3,6-di(2′-pyridyl)-5-tetrazine(19) with 1,4-dihydro-1,4-endoxynaphthalene (20)] with p-toluene-sulfonylacetylene (Scheme [5] ). Analogous generation and trapping of N-Boc isoindole 23 gave compound 8 (62%). To the best of over knowledge these are the first cases concerning the application of the ‘tetrazine method’ to the synthesis of bicyclic α,β-unsaturated sulfones. Full details of the procedure will be reported in due course or upon request.

• 13e For the generation of isobenzofuran, see: Warrener RN. J. Am. Chem. Soc.  1971,  93:  2346 
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14

Typical Experimental Procedure: To a solution of compounds 4-8 (0.43 mmol) in anhyd CH₂Cl₂ (6 mL), NMO (0.86 mmol) was added in one portion under argon at 0 °C. The mixture was allowed to react at r.t. during 24 h. After this time the solvent was removed under reduced pressure and the residual material was purified by column chromatography (hexane-EtOAc, 4:1).