Karoline A. Ostrowski

Towards resource efficient chemistry: tandem reactions with renewables

In an economically expanding world new sustainable concepts have to be developed in order to overcome growing problems of resource availability. Merging different “Green principles” is a promising concept in this respect, e.g. the combination of tandem reactions and renewables. This review summarizes the trends in this field and demonstrates advantages and future demands. Four reactions, namely metathesis, hydroformylation, defunctionalisation and isomerisation, have been identified for transforming renewables in tandem reactions. Every reaction yields a reactive intermediate or secures a tailored selectivity in order to use the natural molecular structure of renewables.

Enantioselective tandem reactions at elevated temperatures: one-pot hydroformylation/SN1 alkylation.

As model substrates for the desired tandemreaction, 1-hexene (1a) as active terminal olefin and alcohol2 as carbocation precursor were chosen. For the hydrofor-mylation, a rhodium precatalyst was selected and synthesisgas (1:1) with pressure of 30 bars was applied.Proline was selected as initial catalyst for the a-alkylationwith additional acid for carbocation generation. In a preced-ing solvent screening, DMF, THF, acetonitrile, and toluenedid not lead to significant conversion (see the Supporting In-formation), whereas the combination of chloroform with tri-fluoroacetic acid gave more encouraging results. Previousexperiments in the a-alkylation had shown Bronsted acidsto be beneficial in the organocatalytic reaction step(Table 1, entry 1).To accelerate the hydroformylation of 1-hexene (1a), sev-eral rhodium precursors were tested in this reaction. Al-though all rhodium precursors were active in this reaction,surprisingly, the frequently used [Rh(CO)

Direct Synthesis of an α,ω-Diester from 2,7-Octadienol as Bulk Feedstock in Three Tandem Catalytic Steps

A new tandem catalytic process was designed and developed as a tool for the direct conversion of the widely available feedstock 2,7-octadienol into an α,ω-diester. This innovative auto-tandem catalysis is atom efficient and consists of three consecutive palladium-catalysed reactions: ether formation, ether carbonylation and alkoxycarbonylation. By using the design of experiments (DoE) approach, significant parameters were determined and the yield of the desired α,ω-diester was optimised. Model substrates allowed deeper insight into the progress of the reaction to be gained and, as a result, the reaction sequence was uncovered. Furthermore, by simply applying other ligands, a different reaction path was followed, allowing other, new tandem catalytic sequences to be explored and enabling new compounds to be obtained.

Decreasing Side Products and Increasing Selectivity in the Tandem Hydroformylation/Acyloin Reaction

A highly selective catalyst system was developed for the recently discovered tandem hydroformylation/acyloin reaction by systematic investigations and changes of reaction conditions. This new catalyst system is characterized by an excellent selectivity of the desired reaction pathway with negligible amounts of side products. A successful application of the tandem hydroformylation/acyloin reaction to a variety of olefins is enabled with comparable excellent selectivities up to >99 % for the first and second reaction step, therefore a general synthesis for the conversion of olefins into acyloins is found. Furthermore, very good to excellent yields for the intermediates and final acyloin products were observed within two catalysed reactions in one preparative step. The acyloin product was applied as a nonpolar precursor for surfactants. After attaching a polar head group to the acyloin and determination of tensiometric data, the molecule showed industrial relevant surface‐active properties.

A general and efficient method for the palladium-catalysed conversion of allylic alcohols into their corresponding dienes

A general method was established, converting a broad range of allylic alcohols directly and quantitatively into their corresponding dienes. The developed protocol allows the direct use of allylic alcohols, circumventing the need for their derivatisation into more reactive precursors, thereby minimising waste production with water as the sole co-product.

Tandem Reactions with Renewables

Tandem catalytic reactions and related processes offer major benefits in comparison with the stepwise synthesis of intermediates and valuable chemicals. Hence, various investigations have been conducted during the last years aiming for the development of selective tandem catalytic systems in numerous chemical disciplines [1, 2, 3, 4, 5, 6, 7, 8]. Generally, in tandem systems, two or more individual chemical transformations are merged together, which minimises on the one hand time and effort.