A novel boron trifluoride etherate mediated deep-seated rearrangement of an α,β-epoxyketone

Acid catalysed reaction of carvone epoxide 2 resulted in dimeric products 3 and 4, in contrast to the expected ring contraction product. Reaction of β-methylcarvone epoxides 8 and 11 with acids furnished 2-acetyl-4-isopropenylcyclopentanones 9 and 14 containing a stereodefined quaternary carbon atom. On the other hand, the reaction of epoxides 8 and 11 with boron trifluoride etherate lacks the stereoselectivity and in addition, anti-epoxide 8 furnished lactone 18 via an unusual deep seated rearrangement.

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(2S,4S)-2-Acetyl-4-isopropenyl-2-methylcyclopentan-1-oneC11H16O2[α]D23=-193 (c 1.82, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (2S,4S)

(2R,4S)-2-Acetyl-4-isopropenyl-2-methylcyclopentan-1-oneC11H16O2[α]D23=-107.9 (c 1.14, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (2R,4S)

(1R,6S)-3,4,6-Trimethyl-7-oxabicyclo[3.3.0.]non-3-en-8-oneC11H16O2[α]D26=+58.8 (c 0.97, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,6S)

(1R,5S,7S)-7-Isopropenyl-4,5-dimethyl-2-[(4-methylphenyl)sulfonyl]-2,3-diazabicyclo[3.3.0]oct-3-en-1-olC18H24N2O3S[α]D24=+21.9 (c 1.51, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,5S,7S)