Carbo-allylic opening of functionalized vinyloxiranes has been investigated with Grignard reagents and, both catalytic and stoichiometric amounts of copper (I) salts. Specifically, α, β-epoxy-γ, δ-unsaturated ketones were found to undergo allylic openings of the epoxy ring in the presence of either CuCN or CuBr.SMe2 in CH2Cl2/THF at -55oC to form δ-substituted-β,γ-unsaturated-α-hydroxyenone in 3 hours. Whiles reactions were conducted with only stoichiometric amounts of CuCN, both stoichiometric and catalytic amounts (5%, 10%, and 20%) of CuSMe2 transferred the alkyl (methyl-, ethyl-, ipropyl-, nbutyl-, and tbutyl-) Grignard reagents to the substrates. Interestingly, it required two equivalents of the allyl and aryl Grignard reagents with one equivalent of the CuSMe2 to achieve 100% conversion. The CuCN catalyzed reactions gave at best 70:30 mixture of the E:Z stereoisomers ( β,γ- double bond) of the products formed. However, all the Cu.SMe2 catalyzed reactions gave 100:0 E:Z selectivity. In the absence of any transition metal salts, a complex mixture of the 1,2-product was obtained with the Grignard reagents. Also, allowing the reaction to warm to and stir at room temperature resulted in the oxidation of the allylic alkoxide intermediate or α-hydroxyenone to δ-substituted-β,γ-unsaturated dione, but the α-hydroxyenone was found to be stable if it was purified by column chromatography immediately after work-up.

Regio- and stereoselective copper (I)-mediated allylic alkylations of α,β-epoxy-γ,δ-unsaturated ketones

251st National Meeting (2016)

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