Stereoselective Conversion of Campholene‐ to Necrodane‐Type Monoterpenes. Novel Access to (−)‐(R,R)‐ and (R,S)‐α‐Necrodol and the Enantiomeric γ‐Necrodols

Abstract

Naturally occurring (-)-(R,R)-a -necrodol ((-)

Chemistry of the pheromones of mealybug and scale insects

“…8 The core monoterpene alcohol structure trans-a-necrodol 342 had been previously identied from a carrion beetle, and synthesized several times. Scheme 52 summarizes the synthesis reported by the Millar group, 120 which combined and optimized elements from previous syntheses of necrodol isomers, including a diastereoselective synthesis of b-necrodol 341, 121 and an efficient isomerization of b-necrodol to a-necrodol 342, 122 the core structure of the pheromone 301. Thus, alkylation of ethyl acetoacetate 336 with bromide 335 followed by intramolecular Knoevenagel condensation gave 332, followed by regioselective decarboxylation to ketoester 338.…”

Absolute Configuration of the Spherical Mealybug Nipaecoccus viridis Sex Pheromone, γ-Necrodyl Isobutyrate: Chemoenzymatic Synthesis and Bioassays

“…Our synthesis is based on a procedure described by Pamingle et al . and optimized by results of other syntheses in the literature (Figure ).…”

“…and optimized by results of other syntheses in the literature (Figure ). The principal change that we made was that the previous procedure used pure enantiomers of (+)-α-pinene and (−)-α-pinene as reagents to obtain (−)-( R )-γ-necrodol and (+)-( S )-γ-necrodol, respectively, while we used a commercially available α-pinene oxide that contained ∼80% (−)-enantiomer (the rest was (+)-α-pinene oxide). Based on our experience with enzymatic separation of terpenic alcohols − and a lipase reaction of ethyl-4-hydroxy-2,2,3-trimethyl cyclopentanecarboxylate, we hypothesized that racemic γ-necrodol could be separated to its two enantiomers by a lipase.…”

“…The decarbonylation of the aldehyde was done with a catalytic amount of Pd/C, as described . The terpene product was reacted with paraformaldehyde followed by treatment with BF 3 ·Et 2 O to give γ-necrodyl acetate . The reaction with Pd/C as a catalyst was expected to cause a significant racemization and resulted in γ-necrodyl acetate consisting of 65% (+) and 35% (−) enantiomer (Figure S2).…”

Bioactive Constituents from the Whole Plants of Gentianella acuta (Michx.) Hulten

“…To determine the sterostructure of it, 4 was treated with β-glucosidase, to give the aglycon, (1 R )-2,2,3-trimethyl-4-hydroxymethylcyclopent-3-ene-1-methanol ( 4 a), which was obtained with negative optical rotation ([α] D −6.5°, CHCl 3 ) and had only one chiral carbon. Using the the same method reported in literatures [ 25 , 26 ], compared optical rotation of 4a with that of its simialr compound, (–)-( R )- γ -necrodol ([α] D −21.2°, CHCl 3 ) [ 27 ], the absolute configuration of 4 was elucidated to be 1 R . Finally, the chemical shift of two methyl at the 2-position was determined by NOE correlations displayed in NOESY experiment.…”