LAUSR

Hydroformylation is an atom-economic and highly efficient transformation from readily available olefins to various synthetically important carbonyl compounds [1]. By using this transformation, the largest amount of fine chemicals have been produced in the global chemical industry every year. However, the toxicity and flammability of the syngas (CO/H2) have hampered application of the conventional hydroformylation into organic synthesis in laboratories and pharmaceutical industry. Therefore, development of new processes using CO/H2 surrogates may further release the synthetic potentiality of hydroformylation. Much effort has been contributed to the research topic, such as hydroformylation of olefins with formaldehyde and alcohols as the syngas surrogates. Besides the hazard and inconvenience of syngas, regioselectivity is also a widely concerned issue for olefin hydroformylation. High regioselctivity for linear aldehyde or for branched aldehyde is highly desirable from the synthetic point of view. Recently, Professor Shi and coworkers [2] reported an interesting Pd-catalyzed hydroformylation of olefins with formic acid as the syngas surrogate based on their previous research on Pd-catalyzed hydrocarboxylation (Figure 1). The studies indicate that ligand is crucial for regioselectivity control. When dppp was employed as the ligand, the reaction displayed excellent regioselectivity toward linear aldehyde. Even for challenging substrates such as styrenes, the corresponding 3-arylpropanals were also obtained in good yields with greater than 20:1 l:b ratios. Complicated substrate (for 2k) and cyclic olefins (for 2l–2m) were also reactive for the hydroformylation. The mechanism for the reaction is very interesting and impressive (Figure 1). Oxidative addition of the palladium catalyst to HCOOAc (3) in situ generated from HCOOH and Ac2O gives palladium hydride species 4, which rearranges to intermediate 5. Complex 5 undergoes hydropalladation toward olefin 1 and migratory insertion to form complex 7. The OAc group of compound 7 is exchanged with the iodide and further replaced by formic acid anion to give intermediate 9. Decarboxylation of 9 and subsequent reductive elimination generate the aldehyde 2 and the Pd(0) catalyst, completing a catalytic cycle. Overall, Professor Shi and coworks have developed an efficient and highly regioselective Pd-catalyzed hydroformylation of olefins by using formic acid as the syngas surrogate. The reaction proceeds under very mild conditions and can be easily handled in the lab without special caution about toxicity and reaction pressure (Figure 1). Owing to the easy operation and high regioselectivity, this transformation has provided a practical method for the preparation of linear aldehydes, and also would stimulate broader application of olefin