We report the first homogeneous palladium-based transfer hydrogenolysis of benzylic alcohols using an in situ formed palladium-phosphine complex and formic acid as reducing agent. The reaction requires a catalyst loading as low as only 1 mol % of palladium and just a slight excess of reductant to obtain the deoxygenated alkylarenes in good to excellent yields. Besides demonstrating the broad applicability for primary, secondary and tertiary benzylic alcohols, a reaction intermediate could be identified. Additionally, it could be shown that partial oxidation of the applied phosphine ligand was beneficial for the course of the reaction, presumably by stabilizing the active catalyst. Reaction profiles and catalyst poisoning experiments were used to characterize the catalyst, the results of which indicate a homogeneous metal complex as the active species.
Herein, we describe the acid/Pd‐tandem‐catalyzed transformation of glycol derivatives into terminal formic esters. Mechanistic investigations show that the substrate undergoes rearrangement to an aldehyde under [1,2] hydrogen migration and cleavage of an oxygen‐based leaving group. The leaving group is trapped as its formic ester, and the aldehyde is reduced and subsequently esterified to a formate. Whereas the rearrangement to the aldehyde is catalyzed by sulfonic acids, the reduction step requires a unique catalyst system comprising a PdII or Pd0 precursor in loadings as low as 0.75 mol % and α,α′‐bis(di‐tert‐butylphosphino)‐o‐xylene as ligand. The reduction step makes use of formic acid as an easy‐to‐handle transfer reductant. The substrate scope of the transformation encompasses both aromatic and aliphatic substrates and a variety of leaving groups.
The goal of this review is to highlight the applications of carbonylation reactions of alkenes in the total synthesis of natural compounds. These highly atom-economic reactions, which are known for their industrial applications, constitute attractive synthetic methodologies for the selective construction of carbonyl compounds. We aimed at the selection of recent methodologically attractive syntheses where carbonylations were applied as key steps. In addition, a few examples of the related carbonylation of allenes are shown.
We regret that we unintentionally omitted to refer to the important pioneering work of James Leighton and his co-workers in our review. This group has substantially contributed both to the development of synthetic methodologies based on hydroformylation and to their application in the total synthesis of natural compounds. Therefore, we would like to add following sentences and references to the original manuscript: Page 1576, left column, second paragraph: the first sentences should be changed to: 'An elegant approach to the synthesis of naturally occurring polyketides using catalytic CC bond-forming reactions, including hydroformylation, was originally described by Leighton in 2011 and later by Krische and co-workers in the synthesis of (+)-zincophorin methyl ester (23). 20 The free acid of this compound is a highly potent antibiotic that was isolated from soil bacteria. 21 Krische's retrosynthesis is based on the construction of fragments A (18) and B (22) and their highly diastereoselective connection at the late stage of the synthesis (Scheme 5).' Accordingly, the reference 20 should be changed to:
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