Enantiospecific synthesis of the tricyclic core structure of lippifolianes

An enantiospecific synthesis of the [6.6.3]-tricyclic carbon framework, 2,6,6,9-tetra-methyltricyclo[5.4.0.02,4]undecane, present in the sesquiterpenes lippifolianes and the diterpenes cyclosclareol, metasequoic acids and parguerols, starting from the readily available monoterpene (R)-carvone, is described.

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Methyl 2-[(1S,2R,6R)-2-(2-methoxymethoxy)-3-methyl-6-(1-methylethenyl)cyclohex-3-enyl]acetateC15H24O4[α]D23=+84.4 (c 7.4, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1S,2R,6R)

Methyl (1R,2S,4R,7S,8R)-(8-methoxymethoxy-2,9-dimethyl-5-oxotricyclo[5.4.0.02,4]undec-9-ene-4-carboxylateC17H24O5[α]D27=-27.6 (c 3.1, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,2S,4R,7S,8R)

Methyl (1R,2S,4R,7R,8R)-8-methoxymethoxy-2,6,6,9-tetramethyl-5-oxotricyclo[5.4.0.02,4]undec-9-ene-4-carboxylateC19H28O5[α]D27=+103 (c 1.4, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,2S,4R,7R,8R)

Methyl (1R,2S,4R,5R,7S,8R)-8-methoxymethoxy-2,9-dimethyl-5-(4-nitrobenzoyloxy)tricyclo[5.4.0.02,4]undec-9-ene-4-carboxylateC24H28N2O4[α]D24=-50.0 (c 1.3, CHCl3)Source of chirality: (R)-carvoneAbsolute configuration: (1R,2S,4R,7S,8R)