An enantiospecific synthesis of a komarovispirane

The enantiospecific total synthesis of a komarovispirane, containing the complete carbon framework, trans-bicyclo[4.3.0]nonanespiro[8.1′]cyclohexane, of the spiroditerpene komarovispirone, starting from the readily available campholenaldehyde is described.

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(1R,3S,6R)-2,2-Dimethyl-3-methoxybicyclo[4.3.0]nonan-8-oneC12H20O3[α]D25=-35.0 (c 3.0, CHCl3)Source of chirality: campholenaldehydeAbsolute configuration: (1R,3S,6R)

Ethyl 2-[(1R,3S,6R,8S)-3-methoxy-2,2-dimethyl-8-(1-methylethenyl)bicyclo[4.3.0]non-8-yl]-acetateC19H32O3[α]D25=+4.4 (c 1.8, CHCl3)Source of chirality: campholenaldehydeAbsolute configuration: (1R,3S,6R,8R)

Ethyl 2-[(1R,3S,6R,8R)-3-methoxy-2,2-dimethyl-8-(1-methylethenyl)bicyclo[4.3.0]non-8-yl]-acetateC19H32O3[α]D25=-4.4 (c 1.8, CHCl3)Source of chirality: campholenaldehydeAbsolute configuration: (1R,3S,6R,8S)

(1R,3S,6R,8R)-3-Methoxy-2,2,2′-trimethyl-bicyclo[4.3.0]nonanespiro[8.1′]cyclohex-2′-en-4′-oneC18H28O2[α]D25=-38.3 (c 0.6, CHCl3)Source of chirality: campholenaldehydeAbsolute configuration: (1R,3S,6R,8R)

(1R,3S,6R,8S)-4′-Isopropylidine-3-methoxy-2,2,2′-trimethylbicyclo[4.3.0]nonanespiro-[8.1′]cyclohex-2′-eneC21H34O[α]D23=+15.0 (c 1.4, CHCl3)Source of chirality: campholenaldehydeAbsolute configuration: (1R,3S,6R,8S)