Chiral synthons from α-pinene: enantioselective syntheses of bicyclo[3.3.0] and [3.2.1]octanones

Enantioselective syntheses of bicyclo[3.3.0]octan-3-one, bicyclo[3.2.1]octan-3-one and bicyclo[3.2.1]octan-2-one derivatives were accomplished by employing a chiron based approach, using intramolecular rhodium carbenoid C–H insertion, acid catalysed cyclisation of α-diazo ketone and intramolecular type II carbonyl ene reactions as key steps.

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(1R,5R)-7,8,8-Trimethylbicyclo[3.3.0]oct-6-en-3-oneC11H16O[α]D25=-42.5 (c 2.0, CHCl3)Source of chirality: α-pineneAbsolute configuration: (1R,5R)

(1S,5R)-7,7-Dimethyl-6-methylenebicyclo[3.2.1]octan-3-oneC11H16O[α]D26=-30.0 (c 3.6, CHCl3)Source of chirality: α-pineneAbsolute configuration: (1S,5R)

Ethyl 4-[(1S)-2,2,3-trimethylcyclopent-3-enyl]-3-oxobutanoateC14H22O3[α]D25=-1.7 (c 14, CHCl3)Source of chirality: α-pineneAbsolute configuration: (1′S)

Ethyl (1S,2R,5R)-2,6,6,7-tetramethyl-3-oxobicyclo[3.3.0]cyclopent-7-ene-2-carboxylateC15H22O3[α]D26=-31.7 (c 0.6, CHCl3)Source of chirality: α-pineneAbsolute configuration: (1S,2R,5R)

(1S,5R)-6,6-Dimethyl-7-methylenebicyclo[3.2.1]octan-2-oneC11H16O[α]D26=-34.0 (c 4.0, CHCl3)Source of chirality: α-pineneAbsolute configuration: (1S,5R)