A NEW ROUTE FOR THE CONVERSION OF CARVONE INTO EUDESMANE SESQUITERPENES

Article abstract of DOI:10.1016/S0040-4020(01)87736-X

The β-hydroxy-α-phenylsulfenyl ketone 2, derived from S-(+)-carvone, was treated with 2 equivalents of the Wittig-Horner phosphine oxide derivative 6 followed by excess methyl iodide to give a ca. 2:3 mixture of the E and Z α-phenylsulfenyl ketones 3a and 3b.The mixture of sulfides was oxidized to the corresponding sulfoxides 3c,d with m-chloroperbenzoic acid.When this mixture refluxed in benzene, elimination of phenylsulfinic acid occured and the intermediate E diene derivative 4a underwent an intramolecular Diels-Alder reaction to give the trans-octalone 5a, the cis-octalone 5c, and another product believed to be the trans-octalone 5b in a 60:28:12 ratio.The Z diene derivative 4b was recovered under these reaction conditions.Wolff-Kishner reduction of the octalone mixture gave (-)-α-selinene (10) as the major product along with the cis-octalin 11 and other unidentified minor products.When the Z diene derivative 4b was heated in toluene at 150 deg C for 48 h, a mixture of octalones having the same composition as that produced above was obtained.Likewise, when the 2:3 mixture of sulfoxides 3c and 3d was heated in toluene at 150 deg C, the same mixture of octalones was produced.Apparently, at the higher temperature, the Z diene derivative 4b isomerized to the E isomer 4a which ultimately underwent the intramolecular Diels-Alder reaction.