[2786-43-8]  · C8H7NSSe  · 3-Methyl-2-selenoxobenzothiazole  · (MW 228.19)

(stereospecifically converts epoxides and episulfides into alkenes1)

Physical Data: mp 114-116 °C.

Solubility: sol acetone, CH2Cl2, THF; slightly sol ether, ethanol; insol H2O.

Form Supplied in: red solid; commercially available.

Handling, Storage, and Precautions: toxic; light sensitive; store in a dark glass bottle.

General Discussion.

The title reagent (1) reacts with epoxides in CH2Cl2 in the presence of stoichiometric quantities of Trifluoroacetic Acid at 0 °C to give the corresponding alkenes almost quantitatively. The method is rapid and stereospecific, proceeding in a fashion that preserves the stereochemistry of the starting epoxide (eq 1).1 Episulfides react under the same conditions, though slowly, to afford alkenes stereospecifically (eq 2).1 Another feature of these reactions is the quantitative recovery of selenium, which may be reused in the synthesis of the reagent.

The mildness of the reaction conditions allows the deoxygenation of epoxides bearing other functionalities, e.g. sugar epoxides (eq 3),2 for which other reagents such as diphenylsilyllithium3 or lithium diphenylphosphide4 cannot be used. In some cases, the deoxygenation occurs with rearrangement (eq 4).2

The synthesis of valienamicin, a branched-chain amino cyclitol, requires a mild deoxygenation of epoxy cyclitol intermediates; this can be accomplished using (1) (eq 5).5

The reagent has also been used for deoxygenation of sterically crowded epoxides to give bicyclic trienes (eq 6).6

The related compound 3-methylbenzothiazole-2-thione (2) [2254-94-6] (mp 91-92 °C, also commercially available) converts epoxides to episulfides stereospecifically under the reaction conditions used for reagent (1) (eq 7).7

1. Caló, V.; Lopez, L.; Mincuzzi, A.; Pesce, G. S 1976, 200.
2. Paulsen, H.; Heiker, F. R.; Feldmann, J.; Heyns, K. S 1980, 636.
3. Reetz, M. T.; Plachky, M. S 1976, 199.
4. Vedejs, E.; Fuchs, P. L. JACS 1973, 95, 822.
5. Paulsen, H.; Heiker, F. R. LA 1981, 2180.
6. Marterer, W.; Prinzbach, H.; Rihs, G.; Wirz, J.; Lecoultre, J.; Heilbronner, E. HCA 1988, 71, 1937.
7. Caló, V.; Lopez, L.; Marchese, L.; Pesce, G. CC 1975, 621.

Vincenzo Caló

University of Bari, Italy

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