Common Strategy for the Synthesis of Some Strychnos Indole Alkaloids.

Indole alkaloids are important natural compounds with interesting bio-activities that can be found in various species belonging to the Amaryllidaceae, Apocynaceae, or Strychnaceae families. Although these compounds have different connections, substituents, and functionalities, their main core can be produced via the formation of a common functionalized tetracyclic subunit, which is rapidly obtained by an oxidative de-aromatization process mediated by a hypervalent iodine reagent from an inexpensive phenol containing a lactate moiety as the chiral auxiliary. A subsequent stereoselective aza-Michael addition and an intramolecular Heck-type reaction lead to the formation of a common key intermediate. This approach provides a solid foundation for the further elaborations of several natural products. The asymmetric syntheses of (-)-strychnopivotine and the polycyclic main cores of (-)-strychnosplendine, (+)-isosplendine, and (+)-malagashanol, three other indole alkaloids, are reported.

Rapid transformation of sulfinate salts into sulfonates promoted by a hypervalent iodine(III) reagent.

An alternative method for forming sulfonates through hypervalent iodine(III) reagent-mediated oxidation of sodium sulfinates has been developed. This transformation involves trapping reactive sulfonium species using alcohols. With additional optimization of the reaction conditions, the method appears extendable to other nucleophiles such as electron-rich aromatic systems or cyclic ethers through a ring opening pathway.

Robust Organocatalysts for the Cleavage of Vegetable Oil Derivatives to Aldehydes through Retrobenzoin Condensation.

A series of thiazolium salts was prepared and tested for the cleavage of the α-hydroxyketone derived from methyl oleate. The robustness of these precatalysts was determined by dynamic thermogravimetric analyses (TGA). It has been shown that the stability of these species is mainly governed by the nature of the counter-anion and some of them were found to be stable until 350-400 °C. The α-hydroxyketone derived from methyl oleate was cleaved under reactive distillation conditions using optimized, thermally robust N-butylthiazolium triflate to give the cleavage product, namely, nonanal and methyl azelaaldehydate, with 85 and 70 % yields. A range of α-hydroxyketones derived from several fatty acids was cleaved to give the corresponding bio-based aldehydes with up to 98 % isolated yields. Finally, this protocol was successfully applied to a high-oleic sunflower oil derivative.

Carbon-Phosphorus Bond Formation on Anilines Mediated by a Hypervalent Iodine Reagent.

Substituted anilines containing a sulfonyl group may be oxidized in situ in the presence of methanol and a hypervalent iodine reagent to form an active iminium species. Subsequent addition of phosphines or phosphites in the same pot produces meta-substituted anilines in good yields. This formal C-H bond functionalization is a direct and efficient means of selectively substituting the meta-position of anilines to produce aromatic phosphonium ions or phosphonates.

One-step formation of dihydrofuranoindoline cores promoted by a hypervalent iodine reagent.

Treatment of various substituted anilines containing a sulfonyl group in the presence of a hypervalent iodine reagent, a perfluorinated alcohol and furan promotes a formal dearomatizing [2 + 3] cycloaddition process, leading to a dihydrofuranoindoline core in useful yields. Thereafter, these functionalized systems can be used for further transformations, yielding potential key intermediates for the total synthesis of complex natural products.

A Stereoselective Arylative-Cyclopropanation Process.

A new stereoselective arylative cyclopropanation process involving treatment of halogenated dienone systems in the presence of a Michael donor containing a nitro-aryl-sulfone has been developed. This transformation enables production of an arylated cyclopropane under mild conditions and occurs via a Michael-Smiles ring closure cascade process, reflecting the concepts of green chemistry and atom economy.

Thiazolylidene-catalyzed cleavage of methyl oleate-derived α-hydroxy ketone to the corresponding free aldehydes.

The thiazolylidene-catalyzed cleavage of the α-hydroxy ketone derived from methyl oleate gave the corresponding aldehydes under nonoxidative conditions through a retro-benzoin process. The aldehydes produced are in equilibrium with their corresponding acyloins. To illustrate the synthetic utility of this protocol, the aldehydes were recovered by distillation.