Synthesis of Optically Active 5-Alkoxy-6-methylcyclohex-2-en-1-ones and 4-Alkoxy-5-methylcyclopent-1-enyl Benzoate

The reaction of (-)-(1E,3Z)-2-methyl-1-((1S)-1-phenylethoxy)penta-1,3-dien-3-ol benzoate with allyltrimethylsilane in SO,- and in the presence of a catalytic amount of Tf2NTMS gives a silyl sulfinate intermediate that furnishes (-)-(6Z,1'S,4S,5S)-5-methyl-4-(1'-phenylethoxy)octa-1,6-dien-6-yl benzoate after acidic workup. The latter undergoes ring-closing, metathesis producing (-)-(2S,3S)-2-methyl-3-((1S)-1-phenylethoxy)cyclopent-5-en-1-yl benzoate. It has been converted also into the corresponding trimethylsilyl enol ether. After oxidation, an enone is obtained that undergoes ring-closing metathesis giving (-)-(5S,6S)-6-methyl-5-((1S)-1-phenylethoxy)cyclohex-2-en-1-one.