Solvent induced isomerization of 2-cyclohexen-1-ol to 3-cyclohexen-1-ol by a chiral lithium amide

Abstract

Enantioselective deprotonation by lithium (S)-1-(2-pyrrolidinylmethyl)pyrrolidine 1 of cyclohexene oxide 2 on changing the solvent from tetrahydrofuran (THF) to cis-2,5-dimethyl-THF (cis-DMTHF) gives the homoallylic alcohol 3-cyclohexen-1-ol 4 up to 74% yield as isomerized product besides the 2-cyclohexen-1-ol 3. In the mixed solvent (THF/cis-DMTHF) 4 was isolated up to 51% yield (25% ee for (S)-4) and 3 in 42% yield (66% ee for (S)-3). In a separate experiment racemic 3 isomerized to racemic 4 in 74% yield when excess of 1 in DMTHF was used.