A practical preparation of versatile cyclohexenoid chiral building blocks

A practical route to two tricyclic chiral building blocks, the acetate 1 and the siloxy ketone 2, serving as powerful chiral cyclohexenoid synthons 3, has been established by employing lipase-mediated kinetic resolution. Thus, the meso-tricyclic ene-1,4-diol 5 furnished the enantiopure monoacetate (+)-1 on reaction with vinyl acetate in THF containing triethylamine in the presence of immobilized lipase (lipase LIP), while the meso-diacetate 6 afforded the enantiomeric monoacetate (-)-1 in enantiopure form on hydrolysis in a phosphate buffer solution in the presence of the same lipase. Under the same enzyme-mediated conditions, the meso-1,4-diol 8 gave the enantiopure monoacetate (+)-10, while the meso-diacetate 9 furnished the enantiomeric monoacetate (-)-10 in enantiopure form. Starting from the former enantiomer (+)-10, both enantiomers of the siloxy-ketone, (+)- and (-)-2, have been prepared enantiodivergently.