Stereo- and regioselective construction of vicinal stereogenic quaternary carbon atoms: enantiospecific approach to cyperanes

An enantiospecific approach to a functionalised carbon framework of the sesquiterpenes, cyperanes, starting from the monoterpene (R)-carvone has been accomplished. A combination of a Claisen rearrangement, intramolecular diazo ketone cyclopropanation and regiospecific cyclopropane ring cleavage has been exploited for the stereo and regiospecific generation of the vicinal stereogenic quaternary carbon atoms.

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(5S)-3-Ethyl-5-isopropenyl-2-methylcyclohex-2-enoneC12H18O[α]D25=+5 (c 1, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (5S)

(1S,5S)-3-Ethyl-5-isopropenyl-2-methylcyclohex-2-enolC12H20O[α]D24=+31.5 (c 2, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,5S)

Ethyl-2-[(1S,5R)-1-ethyl-5-isopropenyl-2-methylcyclohex-2-enyl]acetateC16H26O2[α]D25=+10 (c 1, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,5R)

(1R,2R,4R,6S,9S)-6-Ethyl-4-isopropenyl-1-methyltricyclo[4.3.0.02,9]nonan-8-oneC15H20O[α]D23=+81.5 (c 2, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,2R,4R,6S,9S)

(1S,3R,6R)-1-Ethyl-3-isopropenyl-6-methylbicyclo[4.3.0]nonan-8-oneC15H24O[α]D28=-47.5 (c 1.2, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,3R,6R)

(5S)-3-Benzyl-5-isopropenyl-2-methylcyclohex-2-enoneC17H20O[α]D26=+37.1 (c 3.8, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (5S)

(1S,5S)-3-Benzyl-5-isopropenyl-2-methylcyclohex-2-enolC17H22O[α]D25=+20.9 (c 5.5, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,5S)

Ethyl (1R,5R)-1-benzyl-5-isopropenyl-2-methylcyclohex-2-enylacetateC21H28O2[α]D25=-10.0 (c 0.4, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,5R)

(1R,2R,4R,6R,9S)-6-Benzyl-4-isopropenyl-1-methyltricyclo[4.3.0.02,9]nonan-8-oneC20H24O[α]D22=+64.5 (c 1.8, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,2R,4R,6R,9S)

(1R,3R,6R)-1-Benzyl-3-isopropenyl-6-methylbicyclo[4.3.0]nonan-8-oneC20H26O[α]D22=-55 (c 1.8, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,3R,6R)

(1R,3R,6R)-1-Benzyl-3-isopropyl-6-methylbicyclo[4.3.0]nonan-8-oneC20H28O[α]D26=-42.5 (c 1.6, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,3R,6R)

Methyl [(1S,3R,6R)-3-isopropyl-6-methyl-8-oxobicyclo[4.3.0]non-1-yl]acetateC16H26O[α]D24=-40 (c 0.5, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,3R,6R)

(1R,5S)-3-Benzyl-5-isopropenyl-2-methylcyclohex-2-enyl benzoateC24H26O2[α]D23=+124 (c 1.4, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,5S)

(1R,5S)-3-Benzyl-5-isopropenyl-2-methylcyclohex-2-enolC27H22O[α]D23=+90.2 (c 0.8, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,5S)

Ethyl 2-[(1S,5R)-1-benzyl-5-isopropenyl-2-methylcyclohex-2-enyl]acetateC21H28O2[α]D27=+18 (c 0.5, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,5R)

(1S,2S,4R,6S,9R)-6-Benzyl-4-isopropenyl-1-methyltricyclo[4.3.0.02,9]nonan-8-oneC20H24O[α]D22=-54.5 (c 1.8, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,2S,4R,6S,9R)

(1S,3R,6S)-1-Benzyl-3-isopropenyl-6-methylbicyclo[4.3.0]nonan-8-oneC20H26O[α]D26=-62.5 (c 0.8, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,3R,6S)

(1S,3R,6S)-1-Benzyl-3-isopropyl-6-methylbicyclo[4.3.0]nonan-8-oneC20H28O[α]D25=-70 (c 0.5, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,3R,6S)

Methyl [(1R,3R,6S)-3-isopropenyl-6-methyl-8-oxobicyclo[4.3.0]non-1-yl]acetateC16H26O[α]D23=-57 (c 1, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,3R,6S)