Molecular rearrangement of epoxide derived from sesquiterpenes by Lewis acid catalysis

The molecular rearrangement under mild conditions of two epoxides derived from the sesquiterpenic himachalenes has been studied using BF3·Et2O as the Lewis acid catalyst. Both reactions are efficient and selective affording in each case one new enantiomerically pure ketone isolated in good yield. Their structures have been fully characterized by spectroscopic methods. Mechanisms for the BF3-catalyzed reactions are proposed.

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(1S,3R,7S)-3,11,11-Trimethyltricyclo[5.4.1(3,7).0]dodecan-2-oneC15H24O[α]D25=+6.2 (c 0.5, hexane)Source of chirality: himachaleneAbsolute configuration: (1S,3R,7S)

(1S,2S,3R,6R)-(3,10,10)-Trimethyltricyclo[5.4.4]dodec-4-ene-2-olC15H24O[α]D25=-105 (c 0.5, hexane)Source of chirality: himachaleneAbsolute configuration: (1S,2S,3R,6R)

(1R,7R)-1,5,8,8-Tetramethylbicyclo[5.4.0]undecan-2-oneC15H24O[α]D25=+40.6 (c 0.5, hexane)Source of chirality: himachaleneAbsolute configuration: (1R,7R)