Enantiospecific first total synthesis and confirmation of the relative and absolute stereostructure of isocalamusenone

The enantiospecific total synthesis of two epimers of the sesquiterpene isocalamusenone has been accomplished starting from the readily available monoterpene (R)-limonene, which of the natural product established the stereostructure and the absolute configuration.

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(3R,4S,6R,7S)-6,10-Dimethyl-3-(2-hydroxyprop-2-yl)bicyclo[5.3.0]dec-1(10)-en-4-olC15H26O2[α]D27=+62.8 (c 1.0, CHCl3)Source of chirality: (R)-limoneneAbsolute configuration: (3R,4S,6R,7S)

(3S,6R,7S)-6,10-Dimethyl-3-(2-hydroxyprop-2-yl)bicyclo[5.3.0]dec-1(10)-en-4-oneC15H24O2[α]D26=-81.1 (c 1.6, CHCl3)Source of chirality: (R)-limoneneAbsolute configuration: (3S,6R,7S)

(6R,7S)-3-Isopropylidine-6,10-dimethylbicyclo[5.3.0]dec-1(10)-en-4-oneC15H24O2[α]D28=-6.7 (c 0.7, CHCl3)Source of chirality: (R)-limoneneAbsolute configuration: (6R,7S)

(6S,7S)-3-Isopropylidine-6,10-dimethylbicyclo[5.3.0]dec-1(10)-en-4-oneC15H22O[α]D24=+176.2 (c 0.5, CHCl3)Source of chirality: (R)-limoneneAbsolute configuration: (6S,7S)