Rasta Resin-PPh3-NBniPr2 and its Use in One-Pot Wittig Reaction Cascades

Mo-Catalyzed One-Pot Synthesis of N-Polyheterocycles from Nitroarenes and Glycols with Recycling of the Waste Reduction Byproduct. Substituent-Tuned Photophysical Properties

A catalytic domino reduction-imine formation-intramolecular cyclization-oxidation for the general synthesis of a wide variety of biologically relevant N-polyheterocycles, such as quinoxaline- and quinoline-fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step-economical as well as air- and moisture-tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives.

Reductive Halogenation Reactions: Selective Synthesis of Unsymmetrical α-Haloketones

A method for the selective synthesis of unsymmetrical α-haloketones has been developed. The key transformation is a triphenylphosphine oxide catalyzed reductive halogenation of an α,β-unsaturated ketone in which trichlorosilane is the reducing reagent and an N-halosuccinimide is the electrophilic halogen source. This method allows for a halogen atom to be installed selectively at either of two very similarly substituted sites adjacent to a ketone group.

Reengineering classic organic reactions using polymeric tools

Many of the most widely used reactions in organic synthesis suffer from drawbacks that can hamper their use. For example, the Mitsunobu, Wittig and Appel reactions all result in the formation of a full equivalent of triphenylphosphine oxide, which can be similar in polarity to the desired product, and thus be difficult to remove. Other reactions such as the Suzuki-Miyaura and Mizoroki-Heck reactions require the addition of numerous reagents, ligands and catalysts that can be laborious to separate from the targeted cross-coupled product. This review summarizes our recent work to address these issues by developing polymeric tools designed to simplify product isolation from these transformations.

Rasta resin-triphenylphosphine oxides and their use as recyclable heterogeneous reagent precursors in halogenation reactions

Heterogeneous polymer-supported triphenylphosphine oxides based on the rasta resin architecture have been synthesized, and applied as reagent precursors in a wide range of halogenation reactions. The rasta resin–triphenylphosphine oxides were reacted with either oxalyl chloride or oxalyl bromide to form the corresponding halophosphonium salts, and these in turn were reacted with alcohols, aldehydes, aziridines and epoxides to form halogenated products in high yields after simple purification. The polymer-supported triphenylphosphine oxides formed as a byproduct during these reactions could be recovered and reused numerous times with no appreciable decrease in reactivity.

Multifunctional organic polymeric catalysts and reagents

A series of polystyrenes bearing multiple different functional groups has been synthesized, and these materials have been used as catalysts and reagents in a variety of organic reactions. Polymers functionalized with various combinations of amine, phenol, phosphine, and thiourea groups have been prepared in both non-cross-linked (soluble) and cross-linked (insoluble) formats. Reactions catalyzed by these polymers include Morita–Baylis–Hillman (MBH), alkyne to 1,3-diene isomerization, and decarboxylative Doebner–Knoevenagel reactions. Furthermore, Wittig and tandem Wittig/reduction reactions have been performed using heterogeneous polymeric reagents possessing a combination of amine and phosphine groups.