Enantioselective Synthesis of the Hydroazulene Core of 3α‐Hydroxy‐15‐rippertene

Abstract

As part of a project directed toward the total synthesis of the tetracyclic diterpene 3α‐hydroxy‐15‐rippertene, a constituent of the defense secretion of higher termites, a fast access to two advanced hydroazulene key intermediates has been achieved by starting from (–)‐isopulegol. A regio‐ and diastereoselective formal hydromethallylation and a regioselective ring expansion served as the key steps in the formation of the seven‐membered ring. Completion of the bicyclic title compounds was then achieved by cyclopentene annulation through diastereoselective conjugate addition of organocuprates and subsequent intramolecular aldol condensations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Halogenated and Nonhalogenated Metabolites from the Marine-Alga-Endophytic Fungus Trichoderma asperellum cf44-2

“…In view of the large coupling constants, H-1 was proposed to be axial and opposite to H-6, whereas H-1 was syn to H-3 by their NOE correlation. The relative configurations around ring A was also supported by the identical NMR data with those of an analogue [10]. The relative configurations of exocyclic chiral centers were difficult to be determined.…”

Enantioselective Synthesis of 4‐Desmethyl‐3α‐hydroxy‐15‐rippertene

“…[6] Furthermore, we recently accomplished the enantioselective preparation of the hydroazulene moiety of 1, commencing with (À)-isopulegol. [7] Herein we report on the first enantioselective synthesis of 4-desmethyl-3a-hydroxy-15-rippertene (2), a close analog of 1, starting from the cyclohexanone 5, which is efficiently made in only four steps from (À)-isopulegol. [7] Our synthetic strategy is based on the sequential construction of the ring system in which an intramolecular Diels-Alder reaction [8] is the key transformation for the generation of enol ether 4, which features the tetracyclic skeleton as well as five and six correctly installed stereogenic centers of 1 and 2, respectively.…”

“…[9] Despite variation of the Lewis acid used, the two regioisomers 6 and 7 were always obtained as products. [7] Cycloheptanone 7 could be converted directly into diketone 8 in excellent yield by using potassium osmate catalyzed dihydroxylation [10] of the double bond and subsequent glycol cleavage using sodium periodate. [11] In contrast, transforming 6 into 8 required an additional 1,2-carbonyl shift, [12] which was achieved in six steps with a good overall yield of 57 %.…”

Total synthesis of racemic, natural (+) and unnatural (−) scorzocreticin

“…15 Hydroboration (BH 3 $DMS) followed by oxidation (NaOH and H 2 O 2 ) of the stilbene 8 delivered the primary alcohol 4 in 83% yield. The oxidation of alcohol 4 with the DesseMartin periodinane (DMP) 16 resulted in the corresponding aldehyde that is subsequently used in nucleophilic addition by (4-methoxyphenyl)magnesium bromide, and this in turn resulted in secondary alcohol (AE)-9 in 59% yield. Further, iodination of (AE)-9 with N-iodosuccinimide in chloroform provided the aryl iodide (AE)-2 in 91% yield.…”