Strained rings to assess the "endo preference" of 2-alkyl branched 2-alkenylpotassium species

Upon deprotonation using trimethylsilylmethylpotassium or butyllithium in the presence of potassium tert-butoxide, two allylic organopotassium species are generated from the (E)-isomeric caryophyllene and the (Z)-isomeric isocaryophyllene. Torsional equilibration occurs slowly at -50 DegC (in THF) and rapidly at 0 DegC (in hexane) to afford endo/exo-mixts. of about 95:5 (as evidenced by the isomeric compn. of the trapping products). The relative thermodn. stabilities of the two stereoisomeric organometallic intermediates can be derived by mere superposition of ring-strain differences and the "endo preference" of open-chain (alkylalkenyl)potassium compds. [on SciFinder (R)]