Tandem Hydroformylation/Acyloin Reaction – The Synergy of Metal Catalysis and Organocatalysis Yielding Acyloins Directly from Olefins

Abstract

An ovel, atom efficient, orthogonal tandem catalysisw as developed yieldinga cyloin products( a -hydroxyk etones) directlyf rom olefins under hydroformylation conditions.T he combination of am etal-catalysed hydroformylation anda n organocatalysed acyloin reactionp rovides three atom efficient C À Cb ondf ormations to linear, multifunctional molecules via linkage of the intermediate n-aldehydes.A dditionally,t he rhodium catalyst system gives ah igh n/bra ratio with an exclusive conversion of the terminal doubleb ond in the hydroformylation and the n-aldehydes are converted selectively to theiracyloins.

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

“…This suggests a highly regioselective hydroformylation, by converting only terminal double bonds, if the [rhodium/phosphorous–ligand/carbene–ligand] catalyst complex was applied. This verified our preliminary results17 that no branched aldehydes were observed if 1‐octene was applied and internal double bonds were formed thereof.…”

“…The aforementioned low selectivity resulted from undesired side reactions, which were almost exclusively isomerisation reactions. These reactions were favoured, after applying the optimised conditions to long‐chain molecules 17. Herein, we applied the conditions to 1‐decene ( 1 , Scheme ).…”

“…We then explored the transferability of these optimised conditions (Table 3, no. 3.5) by using the same substrates as in our recent publication,17 because a more accurate comparison was given this way (Table 4). This should reveal whether a suppression of numerous side reactions can be realised by applying other substrates as well.…”

“… [a] Conditions: 6 mmol olefin, 0.03 mmol Rh(CO) 2 acac, 0.09 mmol Nixantphos, 0.6 mmol C2 , 1.2 mmol Et 3 N, 30 bar CO/H 2 (1:1), 5 mL NMP, 90 °C, 16 h. Results determined by GC. [b] 6 mmol olefin, 0.03 mmol Rh(CO) 2 acac, 0.09 mmol Biphephos, 0.6 mmol C1 , 2.4 mmol Et 3 N, 30 bar CO/H 2 (1:1), 5 mL DMF, 60 °C, 16 h 17…”

“…A successful tandem concept merging the hydroformylation with a carbene catalysis was unexplored till our recent publication (Scheme ) 17. Therein, we published the very first example of an orthogonal tandem hydroformylation/acyloin reaction, in which two different catalysts were applied for each transformation:18 A rhodium catalyst and a carbene catalyst.…”