Indium(I)-Mediated, Tandem Carbonyl Addition-Oxy-Cope Rearrangement of γ-Pentadienyl Anions to Cyclohexenones and Conjugated Aromatic Ketones

Abstract

Treatment of 5-bromopenta-1,3-diene with indium metal in the presence of α,β-unsaturated ketones results in initial γ-pentadienylation to generate the hydroxy-1,4-diene. In the case of aromatic conjugated ketones or cyclohexenones the indium alkoxide undergoes spontaneous oxy-Cope rearrangement to afford the 1,4-addition product. The second double bond is required for this [3,3] sigmatropic rearrangement as allyl groups fail to under go this in situ rearrangement. This behavior is consistent with an indium(I) pentadiene species and appears to be the first example of an indium-mediated oxy-Cope rearrangement.

Key words

indium - oxy-Cope - [3,3] sigmatropic rearrangement - γ-pentadienyl - conjugate addition

Reference

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General Procedure: 5-Bromopenta-1,3-diene (7.21 mmol) and the ketone (1.81 mmol) were dissolved in DMF (1.3 mL) at 0 °C. Indium(powder) was added and the reaction was stirred at 21 °C for 4 h. The reaction was diluted with CH₂Cl₂ (5 mL) and Et₂O (15 mL) and filtered through a silica pad and purified by flash chromatography.