Chiral synthesis of maconelliol: a novel cyclobutanoid terpene alcohol from pink hibiscus mealybug, Maconellicoccus hirsutus

A general catalytic synthetic strategy for highly strained methylenecyclobutanes and spiromethylenecyclobutanes

Highly strained methylenecyclobutanes (MCBs) are intriguing scaffolds in synthetic chemistry and drug discovery, but there is no such strategy that enables the synthesis of structurally diverse MCBs with defined stereochemistry. We report a general synthetic strategy for (boromethylene)cyclobutanes (BMCBs) and spiro-BMCBs by a challenging Cu-catalyzed highly chemo-, stereo-, and regioselective borylative cyclization of aliphatic alkynes. This strategy not only enables the installation of various functionalities at each site on the MCB skeleton with unambiguous stereochemistry but also introduces a versatile boromethylene unit that is readily transformable to a wide range of new functional groups; these features significantly expand the structural diversity of MCBs and are particularly valuable in drug discovery. The concise and divergent total syntheses of four cyclobutane-containing natural products were achieved from one common BMCB obtained by this strategy. The origin of the high regioselectivity in the borylcupration of alkynes and the high efficiency of the strained ring cyclization was also studied.

A concise access to bridged [2,2,1] bicyclic lactones with a quaternary stereocenter via stereospecific hydroformylation

Chiral bridged [2,2,1] bicyclic lactones are privileged structural units in pharmaceutics and bioactive nature products. However, the synthetic methods for these compounds are rare. Here we report an efficient method for enantioselective construction of bridged [2,2,1] bicyclic lactones bearing a quaternary stereocenter via Rh-catalyzed asymmetric hydroformylation/intramolecular cyclization/pyridium chlorochromate (PCC) oxidation. By employing a hybrid phosphine-phosphite chiral ligand, a series of cyclopent-3-en-1-ols are transformed into corresponding γ-hydroxyl aldehydes with specific syn-selectivity. Then, hemiacetals form in situ and oxidation with PCC in one-pot affords bridged [2,2,1] bicyclic lactones in high yields and excellent enantiomeric excess. Replacing the hydroxyl group by an ester group, cyclopentanecarbaldehydes with a chiral all-carbon quaternary stereocenter in the γ-position can be generated efficiently.

Sex Pheromone of the Cotton Mealybug, Phenacoccus solenopsis, with an Unusual Cyclobutane Structure

The cotton mealybug, Phenacoccus solenopsis, the distribution of which was formerly limited to Nearctic and Neotropical regions, recently invaded many countries in various regions including Asia, Africa, and the Pacific. More recently, P. solenopsis was newly recorded in Japan and is currently an emerging pest of agricultural crops. In this study, we determined the structure of a sex pheromone of P. solenopsis in order to develop an effective lure for monitoring this pest. From volatiles emitted by virgin adult females, we isolated a compound attractive to males. By means of coupled gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy, we identified this as (2,2-dimethyl-3-isopropylidenecyclobutyl)methyl 3-methylbut-2-enoate. This compound was synthesized and shown to be attractive to male P. solenopsis. Analysis by gas chromatography using an enantioselective stationary phase and polarimetry analyses of the natural pheromone and synthetic enantiomers showed the natural compound to be the (R)-(-)-enantiomer. This compound is an ester of maconelliol, which has an unusual cyclobutane structure found in sex pheromones of other mealybug species, and senecioic acid, also found in the pheromones of other mealybug species. However, this is the first example of the ester of maconelliol and senecioic acid as a natural product.

Chemistry of the pheromones of mealybug and scale insects

This article comprehensively reviews the syntheses of all known sex pheromones of scales and mealybugs, describes how they were identified, and how the synthetic pheromones are used in insect management.