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Polyurethane (PU) is a highly engineered and cross-linked polymer found in a plethora of materials such as mattresses, shoes, windmills, and insulation of refrigerating appliances and buildings. Because of PU's inherent stability, chemical recycling is difficult and often affords a secondary feed with different characteristics and properties compared to the original input. In this work, a simple chemical recycling of PU via a solvolysis process using tert-amyl alcohol both as the solvent and reagent is demonstrated. The devised methodology is showcased for the deconstruction of 20 different PU materials with examples of all four cornerstones of PU (rigid solid, rigid foamed, flexible foamed, and flexible solid). The solvolysis affords both polyol and dianiline fractions, constituting monomeric precursors of PU. The methodology is used for the depolymerization of 50 g flexible PU foam affording a polyol within specification of the original virgin polyol (OH value) and an aniline fraction isolated as the precipitated di-HCl salt with a combined mass recovery of 89 wt%. As the solvolysis process provides access to both the polyol and the aniline precursors of the original isocyanate of PU, the procedure presented in this study could pave the way toward a viable circular economy for PU. A further potential utilization of the method is showcased by valorization of a waste stream from split-phase glycolysis, which is another promising method for recovering polyol from flexible PU foam. Finally, preliminary mechanistic investigations are undertaken to probe the intriguing utility of a hindered tertiary alcohol in a solvolysis procedure.

Industrially, aldehydes are produced annually on a multimillion-tonne scale via the hydroformylation of olefins with syngas (CO/H2 mixture). Nonetheless, this transformation has not found frequent use in the laboratory. Here we report on a simple strategy for the concerted generation of syngas from two accessible and crystalline main element compounds with just water as the primary activator for syngas release. By decoupling the syngas formation and consumption via a two-chamber reactor we demonstrate this low-pressure, low-temperature and near-stoichiometric hydroformylation operates efficiently on a diverse array of terminal olefins without the need for expensive equipment. Our approach provides unique opportunities to access aldehydes in a safe and reliable manner with further adaptation to the synthesis of a range of pharmaceuticals and relevant molecules thereof. This strategy is adaptable to carbon isotope labelling as demonstrated by the use of a 13CO releasing molecule. We anticipate this hydroformylation approach will provide a complementary toolbox for drug discovery and development. Hydroformylation of alkenes is widely used in industry to synthesize aldehydes, but is less prominent in small laboratories due to safety and equipment issues associated with the CO/H2 mixture. This is now addressed by generating stoichiometric syngas from two main element compounds, with water as the activator.

Polyurethane (PU) is a thermoset plastic that is found in everyday objects, such as mattresses and shoes, but also in more sophisticated materials, including windmills and airplanes, and as insulation materials in refrigerators and buildings. Because of extensive inter-cross linkages in PU, current recycling methods are somewhat lacking. In this work, the effective catalytic hydrogenation of PU materials is carried out by applying a catalyst based on the earth-abundant metal manganese, to give amine and polyol fractions, which represent the original monomeric composition. In particular, Mn-PhMACHO is found to catalytically deconstruct flexible foam, molded foams, insulation, and end-of-life materials at 1 wt.% catalyst loading by applying a reaction temperature of 180 °C, 50 bar of H2, and 0.9 wt.% of KOH in isopropyl alcohol. The protocol is showcased in the catalytic deconstruction of 2 g of mattress foam using only 0.13 wt.% catalyst, resulting in 90 % weight recovery and a turnover number of 905.

The [8+2] cycloaddition of indene-2-carbaldehydes and nitro olefins is described to provide benzonorbornene scaffolds in a highly peri-, diastereo-, and enantioselective fashion in the presence of a C2-symmetric aminocatalyst. This reaction, which proceeds through a transient semi-aromatic amino isobenzofulvene, represents the first example of catalytic formation and transformation of these species. Quantum chemical calculations suggest a kinetically controlled stepwise mechanism where the stereochemistry is determined in the first bond-forming event. Beyond the useful [8+2] cycloadducts, [10+4] cycloadducts have been identified in silico as potential off-pathway intermediates.

The first peri- and stereoselective [10+4] cycloaddition between catalytically generated amino isobenzofulvenes and electron-deficient dienes is described. The highly stereoselective catalytic [10+4] cycloaddition exhibits a broad scope with high yields, reflecting a robust higher-order cycloaddition. Experimental and computational investigations support a kinetic distribution of intermediate rotamers dictating the enantioselectivity, which relies heavily on additive effects.

Asymmetric organocatalysis has experienced an incredible development since the beginning of this century. The expansion of the field has led to a large number of efficient types of catalysts. One group, the diarylprolinol silyl ethers, was introduced in 2005 and has been established as one of the most frequently used in aminocatalysis. In this Minireview, we will take a look in the rear-view mirror, ten years after the introduction of the diarylprolinol silyl ethers. We will focus on the perspectives of the different activation modes made available by this catalytic system. Starting with a short introduction to aminocatalysis, we will outline the properties that have made the diarylprolinol silyl ethers a common choice of catalyst. Furthermore, we will describe the major tendencies in the activation and reaction concepts developed with regard to reactivity patterns and combinations with other activation concepts.

A novel organocatalytic activation mode of cyclopropanes is presented. The reaction concept is based on a design in which a reactive donor-acceptor cyclopropane intermediate is generated by in situ condensation of cyclopropylacetaldehydes with an aminocatalyst. The mechanism of this enamine-based activation of cyclopropylacetaldehydes is investigated by the application of a combined computational and experimental approach. The activation can be traced to a favorable orbital interaction between the π-orbital of the enamine and the σ*C-C orbital of the cyclopropyl ring. Furthermore, the synthetic potential of the developed system has been evaluated. By the application of a chiral secondary amine catalyst, the organocatalytically activated cyclopropanes show an unexpected and highly stereoselective formation of cyclobutanes, functionalizing at the usually inert sites of the donor-acceptor cyclopropane. By the application of 3-olefinic oxindoles and benzofuranone, biologically relevant spirocyclobutaneoxindoles and spirocyclobutanebenzofuranone can be obtained in good yields, high diastereomeric ratios, and excellent enantiomeric excesses. The mechanism of the reaction is discussed and two mechanistic proposals are presented.

The highly enantioselective dienamine-mediated formation of 5-bromo-6-(trifluoromethyl)-3,4-dihydro-2H-pyrans from α,β-unsaturated aldehydes and α-bromo-(trifluoromethyl)-enones employing a C2-symmetric aminocatalyst is described. The products are demonstrated to be applicable in coupling reactions directly onto the ring, thereby granting access to a broad scope of highly substituted 6-(trifluoromethyl)-dihydropyran compounds.

The asymmetric formation of spiroindenes containing up to four contiguous stereocenters from the reaction of benzofulvenes with 2,4-dienals through trienamine catalysis is described. The benzofulvene core was found to be an excellent starting point for the synthesis of interesting spiroindenes through a formal cycloaddition pathway. The reaction was mediated by a diphenylprolinol silyl ether catalyst, and a diverse array of spiroindenes were obtained in high yields with excellent stereoselectivity. An attractive feature of the developed system is the possibility to diversify the product scaffold significantly by further manipulation of the chiral spiroindenes. Thus, three intramolecular ring-closing reactions following the organocatalytic step resulted in highly complex polycyclic systems.

An enantioselective synthesis of γ-nitroesters by a one-pot asymmetric Michael addition/oxidative esterification of α,β-unsaturated aldehydes is presented. The procedure is based on merging the enantioselective organocatalytic nitroalkane addition with an N-bromosuccinimide-based oxidation. The γ-nitroesters are obtained in good yields and enantioselectivities, and the method provides an attractive entry to optically active γ-aminoesters, 2-piperidones, and 2-pyrrolidones.

Asymmetric organocatalysis has witnessed a remarkable development since its "re-birth" in the beginning of the millenium. In this rapidly growing field, computational investigations have proven to be an important contribution for the elucidation of mechanisms and rationalizations of the stereochemical outcomes of many of the reaction concepts developed. The improved understanding of mechanistic details has facilitated the further advancement of the field. The diarylprolinol-silyl ethers have since their introduction been one of the most applied catalysts in asymmetric aminocatalysis due to their robustness and generality. Although aminocatalytic methods at first glance appear to follow relatively simple mechanistic principles, more comprehensive computational studies have shown that this notion in some cases is deceiving and that more complex pathways might be operating. In this Account, the application of density functional theory (DFT) and other computational methods on systems catalyzed by the diarylprolinol-silyl ethers is described. It will be illustrated how computational investigations have shed light on the structure and reactivity of important intermediates in aminocatalysis, such as enamines and iminium ions formed from aldehydes and α,β-unsaturated aldehydes, respectively. Enamine and iminium ion catalysis can be classified as HOMO-raising and LUMO-lowering activation modes. In these systems, the exclusive reactivity through one of the possible intermediates is often a requisite for achieving high stereoselectivity; therefore, the appreciation of subtle energy differences has been vital for the efficient development of new stereoselective reactions. The diarylprolinol-silyl ethers have also allowed for novel activation modes for unsaturated aldehydes, which have opened up avenues for the development of new remote functionalization reactions of poly-unsaturated carbonyl compounds via di-, tri-, and tetraenamine intermediates and vinylogous iminium ions. Computational studies have played a pivotal role in the elucidation of the regioselectivities observed for such systems because these pose a challenge due to the presence of multiple reactive sites in these intermediates. Charge distribution and π-orbital coefficient calculations have been applied to explain the observed regioselectivity of the given reactions. The calculation of more elaborate energetic pathways has allowed for in silico identification of high-energy intermediates, such as zwitterions, and transition-state structures, which have also provided information on the driving force controlling the reaction course and outcome.

The enantio- and diastereoselective formation of indenes spirofused to highly substituted cyclopropanes is described. The application of a new cinchona alkaloid derived ammonium salt in a phase transfer catalysis setup facilitates high selectivity and excellent yields at low catalyst loadings (0.1-1.0 mol%).

The enantioselective reaction of bromides (I) and (VI) with unsaturated aldehydes (II) followed by reduction or acetalization of intermediate aldehydes gives rise to alcohols (III) or acetals (VIII), which are readily converted into dihydropyran derivatives (V) and (X).

Vinyl phosphonates (II) and (VIII) as well as nitro olefins (XI) and (XIII) react with annulated cyclic enals (I), (IV), (VI) and (X) to carbocyclic derivatives (III), (V), (VII), (IX), (XII), and (XIV) in a highly regio- and enantioselective manner using proline-based derivatives as chiral catalysts.

A facile one-pot protocol for the synthesis of steroids via Diels—Alder reaction of enals with cyclic dienophiles in the presence of catalytic amounts of Tms-diphenylprolinol (PRS) is developed.

Attractive carbocyclic structures are accessed via a highly regio- and enantioselective aminocatalytic gamma-addition of cyclic enals to vinyl phosphonates followed by a one-pot intramolecular Horner-Wadsworth-Emmons reaction. It is also demonstrated that nitro olefins can act as electrophiles in a similar reaction concept, providing carbocycles in equally high stereoselectivity.

In the reaction of some aldehydes (V), formation of acetal by-products is inhibited by increasing the amount of NBS.

Various title systems bearing 5 stereogenic centers are prepared with excellent enantioselectivities in a one-pot manner.

An efficient one-pot procedure that provides a direct access to polycyclic hexahydrocyclopenta[b]quinoline derivatives having five stereogenic centers has been developed. The system displays great tolerance toward different aldehydes, anilines, and nitroalkenes. The products are obtained in high yields and excellent enantio- and diastereoselectivities.