Selenium transfer reagent: one-step alkoxyselenation of cyclohexene with bis(2-bromoethyl)selenium dibromide

Abstract

The reaction of bis(2-bromoethyl) selenium dibromide 1 with cyclohexene 2 in alcohol under reduced pressure proceeds smoothly to give bis(2-alkoxycyclohexyl) selenium dibromide (R = Me 4, R = Et 5, R = Prⁱ6)via 2-bromocyclohexyl-2′-bromoethylselenium dibromide 3 as an intermediate together with ethene. The diastereoisomers 4a and 5a (1R,2R,1′S,2′S) and 4b and 5b(1R,2R,1′R,2′R or 1S,2S,1′S,2′S) were separated from 4 and/or 5. These isomers 4a/5a and 4b/5b were isolated as a meso and a racemic mixture, respectively. Although the addition product 6a(1R,2R,1′S,2′S) was only isolated from 6 in the meso form, the corresponding diastereoisomer 6b(1R,2R,1′R,2′R or 1S,2S,1′S,2′S) was not detected. These results indicated that the Se and Br atoms in the cyclohexane ring of 3, and the Se and alkoxy groups in the cyclohexane rings of 4–6 were in the diequatorial position.