- The enantioselective syntheses of bisabolane sesquiterpenes Lepistirone and Cheimonophyllon E
-
The synthetic approach to the bisabolane sesquiterpenes Lepistirone 1 and Cheimonophyllon E 2 involves the transformation of (+)-2-carene (5) into the p-menthane furans 8 and 11. Regio- and stereoselective alkylation, and standard reactions complete the e
- Brocksom, Timothy John,Zanotto, Paulo R.,Brocksom, Ursula
-
p. 2397 - 2398
(2007/10/03)
-
- Asymmetric total syntheses of (+)-cheimonophyllon E and (+)-cheimonophyllal
-
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).
- Takao, Ken-ichi,Tsujita, Tomohiro,Hara, Manabu,Tadano, Kin-ichi
-
p. 6690 - 6698
(2007/10/03)
-
- Total synthesis of (+)-cheimonophyllon E, a bisabolane sesquiterpenoid
-
Total synthesis of (±)-cheimonophyllon E was accomplished starting from 3-methyl-2-cyclohexen-1-one. Also, synthesis of (+)-cheimonophyllon E, the natural enantiomer, was achieved through optical resolution of a key intermediate in the racemic synthesis.
- Takao, Ken-Ichi,Hara, Manabu,Tsujita, Tomohiro,Yoshida, Ken-Ichi,Tadano, Kin-Ichi
-
p. 4665 - 4668
(2007/10/03)
-