Wittig- and Horner–Wadsworth–Emmons-Olefination Reactions with Stabilised and Semi-Stabilised Phosphoranes and Phosphonates under Non-Classical Conditions

A Triphenylphosphine-Based Microporous Polymer for a Wittig Reaction Cycle in the Solid State

The Wittig reaction is a key step in industrial processes to synthesise large quantities of vitamin A and various other important chemicals that are used in daily life. This article presents a pathway to achieve the Wittig reaction in a solid network. A highly porous triphenylphosphine-based polymer was applied as a solid Wittig reagent that undergoes, in a multi-step cycle, in total six post-synthetic modifications. This allowed for regeneration of the solid Wittig reagent and reuse for the same reaction cycle. Of particular industrial relevance is that the newly developed material also enables a simple way of separating the product by filtration. Therefore, additional costly and difficult separation and purification steps are no longer needed.

Wittig/B─H insertion reaction: A unique access to trisubstituted Z-alkenes

The Wittig reaction, which is one of the most effective methods for synthesizing alkenes from carbonyl compounds, generally gives thermodynamically stable E-alkenes, and synthesis of trisubstituted Z-alkenes from ketones presents notable challenges. Here, we report what we refer to as Wittig/B─H insertion reactions, which innovatively combine a Wittig reaction with carbene insertion into a B─H bond and constitute a promising method for the synthesis of thermodynamically unstable trisubstituted Z-boryl alkenes. Combined with the easy transformations of boryl group, this methodology provides efficient access to a variety of previously unavailable trisubstituted Z-alkenes and thus provides a platform for discovery of pharmaceuticals. The unique Z-selectivity of the reaction is determined by the maximum overlap of the orbitals between the B─H bond of the borane adduct and the alkylidene carbene intermediate in the transition state.

Unusual Application for Phosphonium Salts and Phosphoranes: Synthesis of Chalcogenides

A novel strategy for the synthesis of sulfides and selenides from phosphonium salts and thio- or selenesulfonates, commercially available compounds, is described. When phosphoranes were used in the reaction, different products were obtained. The methodology does not require the use of metals, reactive species, or anhydrous conditions to be performed.

Transformation of Corn Lignin into Sun Cream Ingredients

Production of value-added chemicals from lignocellulose is one of the key strands of the emerging bio-economy. A synthetic approach has been developed to produce p-methoxy coumarate esters from waste corn stover and corn bran, and further transform these compounds into consumer products. In the first step, p-coumaric acid (pCA) and ferulic acid (FA) are released through mild alkaline hydrolysis of corn waste, in more than 20 mg g^-1 yield (10 wt % based on lignin content). Subsequently, heterogeneous solid acids catalyze the esterification of pCA with various alcohols. Amberlite IR-15 shows the best catalytic performance, owing to its optimal acid density, large surface area, and suitable pore diameter. The solid acid catalyst can be recycled with slight activity loss and regenerated by acid washing and vacuum drying. Finally, methylation of p-coumarate ester to give target product p-methoxy coumarate esters is carried out by using commercially available and low-cost inorganic bases (e. g., K₂ CO₃ ). Base-catalyzed transesterification of methyl p-methoxy coumarate to p-methoxy coumarate esters is also investigated.

Synthesis of Butenolides via a Horner-Wadsworth-Emmons Cascading Dimerization Reaction

The efficient synthesis of a range of structurally related butenolides has been observed while we were exploring the substrate-scope of a Horner-Wadsworth-Emmons (HWE) reaction. While aliphatic aldehydes gave the expected HWE product, aromatic aldehydes furnished butenolides, resulting from the dimerization of the HWE product during desilylation of the initially formed HWE adduct. In addition to isolating butenolides in a high yield, we have also determined precisely when dimerization occurs.

Silica Gel as a Promoter of Sequential Aza-Michael/Michael Reactions of Amines and Propiolic Esters: Solvent- and Metal-Free Synthesis of Polyfunctionalized Conjugated Dienes

We present an efficient, simple, metal- and solvent-free silica-gel-promoted synthesis of functionalized conjugated dienes by sequential aza-Michael/Michael reactions by starting from commercially available primary amines and propiolic esters. The scope and usefulness of the method is demonstrated for 31 examples, including a range of propiolic esters, aliphatic amines, and differently substituted aromatic amines. For aliphatic amines, the products were obtained within 0.5 to 4 h in 52 to 85 % yield, compared with 3.5 to 22 h under classical solution-phase synthesis, which proceeds with similar or lower yields. The method was found to be particularly useful for weakly nucleophilic aromatic amines, which provided products in 21 to 73 % yield over 2.5 to 9.5 h compared with yields of 0 to 49 % over 1 to 6 d under standard solution-phase conditions, and for more hydrophobic esters that gave products in yields of 47 to 79 % over 1 to 3 h compared with 0 to 45 % over 4 to 114 h in solvent.

Oxidative Dephosphorylation of Benzylic Phosphonates with Dioxygen Generating Symmetrical trans-Stilbenes

Under a dioxygen atmosphere, benzylphosphonates and related phosphoryl compounds can readily produce the corresponding trans-stilbenes in high yields with high selectivity upon treatment with bases. Various functional groups were tolerable under the reaction conditions.

Unsymmetrical E-Alkenes from the Stereoselective Reductive Coupling of Two Aldehydes

The unprecedented formation of unsymmetrical alkenes from the intermolecular reductive coupling of two different aldehydes is described. In contrast to the McMurry reaction which affords statistical product mixtures, selectivity in the reported procedure is achieved by a sequential ionic mechanism in which a first aldehyde is reacted with a phosphanylphosphonate to afford a phosphaalkene intermediate which, upon activation by hydroxide, reacts with a second aldehyde to the unsymmetrical E-alkenes. The described reaction is free of transition metals and proceeds under ambient temperature within minutes in good to excellent overall yields. It is a new methodology to use feedstock aldehydes for the direct production of C═C double bond-containing products and may impact how chemists think of multistep synthetic sequences in the future.