Convenient Synthesis of meso-Cyclohexa-1,3-dienes by One-Pot Two-Step Deoxygenation of 7-Oxabicyclo[2.2.1]hept-2-enes

Abstract

Iron(III) hydroxide oxide was found to be an efficient catalyst for the ring-opening reaction of 5,6-cis-disubstituted 7-oxa­bicyclo[2.2.1]hept-2-enes with acetyl bromide in dichloromethane at room temperature to give cyclohexene derivatives with leaving groups (acetoxy or bromo groups) disposed on each allylic position. A successive one-pot treatment of the reaction mixture with zinc powder and tetrahydrofuran successfully induced reductive 1,4-elimination to afford synthetically useful 5,6-disubstituted meso-cyclohexa-1,3-dienes in good-to-high yields.

Key words

catalysis - ring opening - furans - reductions - eliminations - cyclohexadienes

References

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11

The present ring-opening reaction is apparently nonstereospecific in contrast to those reported by Seçen, which are retentive and directed by a neighboring-group effect (see ref. 7).

12

Upon addition of AcBr to a yellow suspension of FeO(OH) in CH₂Cl₂, a dark-red homogeneous solution was obtained.

14

Water was not intentionally added, but the reductive elimination was carried out in open air so that the AcBr was probably hydrolyzed to AcOH.

15

In large-scale reactions, the second step of the present one-pot protocol should be performed at 0 ˚C because it is significantly exothermic.