Asymmetric total syntheses of (+)-cheimonophyllon E and (+)-cheimonophyllal

Ken ichi Takao, Tomohiro Tsujita, Manabu Hara, Kin ichi Tadano

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14 Citations (Scopus)

Abstract

The highly enantiocontrolled total syntheses of natural (+)-cheimonophyllon E (5) and (+)-cheimonophyllal (6), biologically intriguing oxygenated bisabolane-type sesquiterpenoids, have been completed. The present synthetic strategy featured the use of an asymmetric aldol-type reaction for preparing in the first synthetic step an optically active 6-C-substituted 3-methyl-2-cyclohexenone derivative. Thus, a Mukaiyama aldol reaction of 1-methyl-3-silyloxy-1,3-cyclohexadiene 31 with α,β-unsaturated aldehyde 11 in the presence of a chiral (acyloxy)borane (CAB)-type Yamamoto catalyst 33 proceeded with high levels of both diastereo- and enantioselectivities. The predominant aldol adduct, syn-9, was transformed into γ,δ-epoxy allylic alcohol 8 by a nine-step sequence, including the substrate-controlled 1,2-reduction of enone, syn-12, also the epoxidation of allylic alcohol 15. Epoxy-alcohol 8 underwent 5-exo-cyclization in a high regioselective manner under acidic conditions to produce a bicyclic key intermediate (+)-7, which was eventually efficiently converted to (+)-cheimonophyllon E (5) or (+)-cheimonophyllal (6).

Original languageEnglish
Pages (from-to)6690-6698
Number of pages9
JournalJournal of Organic Chemistry
Volume67
Issue number19
DOIs
Publication statusPublished - 2002 Sep 20

ASJC Scopus subject areas

  • Organic Chemistry

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