Development of a Terpene Feedstock-Based Oxidative Synthetic Approach to the Illicium Sesquiterpenes

Synthesis, structures and reduction chemistry of monophthalocyanine scandium hydroxides

The preparation and structural characterization of a pair of scandium(III) phthalocyanine hydroxide complexes were achieved by reaction of PcScCl with alkali metal alkoxides, likely via hydrolysis of soluble PcSc-alkoxide intermediates. A Sc[Formula: see text]Li[Formula: see text]-OH)[Formula: see text] cubane supported by two distorted Pc rings of the form (PcSc)[Formula: see text]-OH)[Formula: see text]Li[Formula: see text](THF)(DME) was isolated from the reaction of PcScCl with LiO[Formula: see text]Pr, while a simpler alkali-metal-free [Pc[Formula: see text]Sc[Formula: see text]-OH)[Formula: see text](THF)] was obtained from addition of NaO[Formula: see text]Bu; both structures are reminiscent of bent metallocenes, with dihedral angles between the two Pc rings of 50.8 and 37.7[Formula: see text]respectively. A soluble PcScOH material can also be obtained directly via hydrolysis of insoluble PcScCl in approximately 95:5 THF:water. Reduction of the Pc ring of PcScCl using KC[Formula: see text] is reversible and generates Pc[Formula: see text] and Pc[Formula: see text]-containing materials that were characterized via UV-vis spectroscopy and, where appropriate EPR and [Formula: see text]H NMR spectroscopy; analogous reductions of the PcScOH-based species were irreversible. Exposure of the air-sensitive, reduced PcScCl-based species to ambient atmosphere generated PcScOH materials analogous to the direct hydrolysis route.

Iron- and cobalt-catalyzed C(sp3)–H bond functionalization reactions and their application in organic synthesis

This review highlights the developments in iron and cobalt catalyzed C(sp³)–H bond functionalization reactions with emphasis on their applications in organic synthesis, i.e. natural products and pharmaceuticals synthesis and/or modification.

A Gallium-based Chiral Solvating Agent Enables the Use of 1H NMR Spectroscopy to Differentiate Chiral Alcohols

In situ, direct 1H NMR chiral analysis by using chiral solvating agents is a convenient and efficient analytical technique. Here we developed a Ga-based chiral anionic metal complex for 1H NMR chiral analysis of alcohols. Utilizing the optimal pKa value, the Ga complex was able to differentiate 1H NMR signals of each (R)- and (S)-enantiomer of alcohols, measured at room temperature. This direct 1H NMR chiral analysis of alcohols was used to rapidly determine enantiomeric excess and conversion in a kinetic resolution and an asymmetric synthesis.

Allylative Approaches to the Synthesis of Complex Guaianolide Sesquiterpenes from Apiaceae and Asteraceae

With hundreds of unique members isolated to date, guaianolide lactones represent a particularly prolific class of terpene natural products. Given their extensive documented therapeutic properties and fascinating chemical structures, these metabolites have captivated the synthetic chemistry community for many decades. As a result of divergent biosynthetic pathways, which produce a wide array of stereochemical and oxidative permutations, a unifying synthetic pathway to this broad family of natural products is challenging. Herein we document the evolution of a chiral-pool-based synthetic program aimed at accessing an assortment of guaianolides, particularly those from the plant family Apiaceae as well as Asteraceae, members of which possess distinct chemical substructures and necessitate deviating synthetic platforms. An initial route employing the linear monoterpene linalool generated a lower oxidation state guaianolide but was not compatible with the majority of family members. A double-allylation disconnection using a carvone-derived fragment was then developed to access first an Asteraceae-type guaianolide and then various Apiaceae congeners. Finally, using these findings in conjunction with a tandem polyoxygenation cascade, we developed a pathway to highly oxygenated nortrilobolide. A variety of interesting observations in metal-mediated aldehyde allylation and alkene polyoxygenation are reported and discussed.

Juniperanol: First total synthesis and evaluation in Type 2 Diabetes disease

The first total synthesis of juniperanol, the tricyclic sesquiterpenoid enantiomer of α-cedrol is described. The synthesis relies on stereoselective gold-catalyzed Ohloff-type propargylic ester rearrangement performed on a 10 g scale, and a carbocationic cascade in the presence of acetyl methanesulfonate. The ability of juniperanol to interfere in glucose processes in different cell types is described.

Total Synthesis and Structure Revision of (-)-Illisimonin A, a Neuroprotective Sesquiterpenoid from the Fruits of Illicium simonsii

Illisimonin A was isolated from Illicium simonsii and has a previously unreported tricyclic carbon framework. It displayed neuroprotective effects against oxygen-glucose deprivation-induced cell injury in SH-SY5Y cells. It incorporates a highly strained trans-pentalene ring system. We report the first synthesis of (±)-illisimonin A. Notable steps in the route include a 1,3-dioxa-2-silacyclohexene templated Diels-Alder cycloaddition and type-3 semipinacol rearrangement to generate the trans-pentalene. The final step is an iron-catalyzed C-H oxidation. The synthetic route is robust, with 94 mg of racemic material prepared in a single pass. Resolving an intermediate enabled the synthesis of natural (-)-illisimonin A. The absolute configuration of (-)-illisimonin A was revised to 1S,4S,5S,6S,7R,9R,10R based on the X-ray structure of a heavy-atom analogue.

Asymmetric total synthesis of (+)-astellatol and (−)-astellatene

Here we describe the full account of the total synthesis of (+)-astellatol, as well as the first total synthesis of (−)-astellatene.