ChemInform Abstract: Asymmetric Hydroformylation of Z‐Enamides and Enol Esters with Rhodium‐Bisdiazaphos Catalysts.

Abrams, M. Leigh; Foarta, Floriana; Landis, Clark R.

doi:10.1002/chin.201515061

Cited by 1 publication

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“…Previous studies of AHF from the Landis group showed that 1,2-disubstituted alkenes bearing groups that withdraw electron density through the σ framework, including enol esters, enamides, vinyl arenes, vinyl fluorides, or acrylates, did not follow the general steric preference for the linear aldehyde products and instead favored the branched regioisomer. 2b, 5 We hypothesized that strong electron-withdrawing groups might also promote the branched-selective AHF of a range of 1,1′disubstituted alkenes to give tetrasubstituted aldehydes, a proposal that is supported by the results in Scheme 1. As a complement to electronic control, we were also curious to explore the potential of ring strain to improve the reactivity and branch-selectivity of Rh-catalyzed hydroformylations.…”

Section: ■ Introductionmentioning

confidence: 93%

“…Interestingly, rates obtained with 1,1′-alkenes (up to 50 turnovers/h, Table 3, entries 1 and 3) can surpass those previously observed for 1,2-disubstituted enol esters and enamides (up to 17 turnovers/h) under the same conditions. 5 In general, ligand L1 yields faster and more selective AHF than L2, although L2 shows better selectivity for alkylsubstituted acrylates, such as 8 and 9 (Table 3, entries 8 and 9) and α-methylene-γ-butyrolactone (entry 10). Thus, when screening new substrates, it is advisible to try both L1 and L2.…”

Section: ■ Introductionmentioning

confidence: 96%

“…4 In comparison to AHF reactions of monosubstituted alkenes, the analogous transformations of 1,1′-and 1,2disubstituted alkenes have been significantly more challenging and display limited scope. 5 In particular, 1,1′-alkene AHF reactions are scarcely reported, proceed more slowly than those of mono-or 1,2-disubstituted alkenes, and tend to favor linear selectivity (according to Keuleman's rule). 6 Despite the volume of literature describing enantioselective hydroformylation, only four examples of distinct 1,1′-disubstituted alkenes undergoing branch-selective AHF have been reported (Scheme 1).…”

Section: ■ Introductionmentioning

confidence: 99%

“…This substrate class was chosen due to previous results showing that ester groups in 1,2-disubstituted alkenes could direct the regioselectivity in hydroformylation. 5 Acrylates 1−10 were tested in the presence of both (S,S,S)-BisDiazaphos (L1) and (S,S)-Ph-BPE (L2). As previously mentioned, the methyl ester of 2fluoropropenoic acid 1 (entry 1) gave excellent selectivity for the branched aldehyde 1b and a good ee of 85% using L1.…”

Section: ■ Introductionmentioning

confidence: 99%

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α-Tetrasubstituted Aldehydes through Electronic and Strain-Controlled Branch-Selective Stereoselective Hydroformylation

et al. 2018

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Hydroformylation utilizes dihydrogen, carbon monoxide, and a catalyst to transform alkenes into aldehydes. This work applies chiral bisdiazaphospholane (BDP)- and bisphospholanoethane-ligated rhodium complexes to the hydroformylation of a variety of alkenes to produce chiral tetrasubstituted aldehydes. 1,1'-Disubstituted acrylates bearing electron-withdrawing substituents undergo hydroformylation under mild conditions (1 mol % of catalyst/BDP ligand, 150 psig gas, 60 °C) with high conversions and yields of tetrasubstituted aldehydes (e.g., 13:1 regioselectivity, 85% ee, and <1% hydrogenation for 1-fluoromethyl acrylate). The scope also encompasses both acyclic 1,1'-disubstituted and trisubstituted, electron-poor alkenes as well as di- and trisubstituted alkenes composed of small rings with exocyclic and endocyclic unsaturation. For example, 1-methylene-β-lactam furnished the tetrasubstituted aldehyde with 98% selectivity and up to 83% ee. Notably, chiral trisubstituted bicyclic methyleneaziridines are transformed with >99% regioselectivity and >19:1 diastereoselectivity to tetrasubstituted aldehydes at rates >50 catalyst turnovers/hour. NMR studies of the noncatalytic reaction of HRh(BDP)(CO) with methyl 1-fluoroacrylate enable interception of tertiary alkylrhodium intermediates, demonstrating migratory insertion to acyl species is slower than formation of secondary and primary alkylrhodium intermediates. Overall, these investigations reveal how the interplay of sterics, electronics, and ring strain are harnessed to provide access to valuable α-tetrasubstituted aldehyde synthetic building blocks by promoting branched-selective hydroformylation.

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Section: ■ Introductionmentioning

confidence: 93%

Section: ■ Introductionmentioning

confidence: 96%