Reductive coupling of two aldehydes to unsymmetrical E-alkenes via phosphaalkene and phosphinate intermediates

Abstract

Stilbenes with push-pull electronics are directly accessible from an electron-rich and an electron-deficient benzaldehyde in a novel reductive aldehyde cross-coupling reaction. The one-pot procedure is enabled by the oxidation of a transient phosphinite to the corresponding phosphinate which exhibits sufficient reactivity towards deactivated aldehydes.

Triphenylphosphaalkenes in Chemical Equilibria

“…In order to get quantitative information from the 31 P NMR spectroscopic monitoring of the reactions, an internal standard was used. We decided to use a Mes*‐phosphaalkene, more specifically [( E )‐(4‐methoxybenzylidene) (2,4,6‐tri‐ tert ‐butylphenyl)phosphane] as internal standard since it has been shown to have a high chemical stability and a similar relaxation time as phosphaalkenes 1a – c . A typical example of such a 31 P NMR reaction monitoring starting from ketone a is shown in Figure .…”

“…We have recently reported such a process in which phosphaalkenes are key intermediates for the reductive cross‐coupling of aldehydes to alkenes . By using Mes* and Mes to stabilize the P=C double bonds, 1,2‐disubstituted olefins can be synthesized in a one‐pot reaction. P ‐phenyl substituted phosphaalkenes are most likely even more reactive and may allow an even broader substrate scope in terms of carbonyl compounds that could be used for the reductive carbonyl‐to‐alkene cross‐coupling chemistry.…”

Reactivity patterns of benzhydryl(mesityl)phosphane oxide – a potential intermediate in carbonyl-carbonyl coupling reactions?

“…These may include future work to decrease the steric demand of the P-substituent further, possibly together with an increase of oxygenation level of the P-center. [12,13] Experimental General experimental procedures. 1 H, 13 atmosphere.…”

“…Recently our group published a procedure which allows the formation of C ¼ C doubles bond by the direct coupling of two aldehydes (Figure 1a, b). [11][12][13] In contrast to the McMurry protocol [14] which uses low-valent transitional metals, requires harsh reaction conditions, and does not allow the selective preparation of unsymmetric alkenes from the coupling of two non-identical carbonyl compounds, our approach proceeds by a stepwise anionic mechanism which resolves the drawbacks mentioned above. In our synthetic methodology, [11] a first aldehyde reacts with a lithiated phosphanylphosphonate to obtain phosphaalkenes in which the C-center of the P ¼ C double bond exhibits an opposite polarization compared to that in the starting carbonyl compound (Figure 1b).…”

E,Z-Selectivity in the reductive cross-coupling of two benzaldehydes to stilbenes under substrate control

“…29,31 In recent years, we have been interested in developing new phosphorus mediated cross-coupling reactions of carbonyl compounds to olefins. [32][33][34][35] In one of our latest work, we have been able to couple two different benzaldehydes selectively to unsymmetrical 1,2-disubstituted stilbenes via phosphaalkene (2) and phosphinate (3) intermediates (Scheme 2). 34 In this one-pot reaction, a first benzaldehyde A is converted to a phosphaalkene 2 which proceeds under Umpolung of the carbonylcarbon.…”