Chapter 16.4, Problem 8ATS

Q4 B-Damascenone belongs to a family of fragrant natural products called rose ketones that have been used in the perfume industry. In one synthesis of B-damascenone, the reaction of compound 1 with one equivalent of MCPBA afforded two constitutionally isomeric epoxides (compounds 2 and 3), which were then converted into diol 4 upon treatment with aqueous acid. Identify the structures of epoxides 2 and 3, and propose a mechanism that converts each of them into compound 4 in the presence of H,O*. (Note: It is reasonable to presume that a protonated epoxide can open by itself, without the involvement of a nucleophile, if doing so will give a resonance-stabilized allylic carbocation intermediate.)? OCH, OH OCH3 H,O 2+3 MCPBA (one equiv.) 4 OH B-Damascenone

B-Damascenone belongs to a family of fragrant natural products called rose ketones that have been used in the perfume industry. In one synthesis of B-damascenone, the reaction of compound 1 with one equivalent of MCPBA afforded two constitutionally isomeric epoxides (compounds 2 and 3), which were then converted into diol 4 upon subsequent treatment with aqueous acid. Identify the structures of epoxides 2 and 3, and propose a mechanism that converts each of them into compound 4 in the presence of H30+. OCH, OH OCH, МСВРА 2 +3 (one equiv.) OH B-Damascenone

Ibufenac, a para-disubstituted arene with the structureHO2CCH2C6H4CH2CH(CH3)2 , is a much more potent analgesic thanaspirin, but it was never sold commercially because it caused livertoxicity in some clinical trials. Devise a synthesis of ibufenac frombenzene and organic halides having fewer than five carbons.