A novel self-promoted Morita-Baylis-Hillman-like dimerization

Abstract

While stable in CH 2 Cl 2 , hexane or THF, in the presence of MeOH, self-promoted dimerization of the triarylphosphine-alkene 1, a ligand for Pd-catalyzed reactions, produced an unusual racemic bis(phosphine) 2 in high yield. The reaction of 2 with Pd(dba) 2 , followed by oxidative addition of p-IC 6 H 4 NO 2 , yielded a trans-chelated Pd(II) aryl iodide complex. phosphine, ligand, palladium, DFT calculations, reaction mechanism Citation:Li Q, Wongkhan K, Luo X C, et al. A novel self-promoted Morita-Baylis-Hillman-like dimerization.The Morita-Baylis-Hillman (MBH) reaction [1,2] is a useful and atom-economical carbon-carbon bond forming reaction (Scheme 1), involving nucleophile catalyzed addition of an alkene, which is activated by an electron-withdrawing group, to an electrophile, typically an aldehyde or imine [3]. As it has been used for the synthesis of a variety of natural and unnatural products [4-6], the MBH reaction has become increasingly significant [3,[7][8][9][10][11][12][13][14][15][16][17][18][19]. However, the application of the MBH reaction had been limited in complex syntheses by slow reaction rates and low conversions [3,20] as well as problems in controlling absolute stereochemistry [8]. Theoretical and experimental studies have provided insight into how to increase the rate of this reaction [21][22][23][24][25]. Nucleophilic catalysts such as DABCO, DBU, and n-Bu 3 P are frequently employed [20]. Slow reaction rates [20], autocatalysis in the absence of proton donors [22], formation of dioxanones [26,27], and the rate acceleration observed in protic solvents [28][29][30][31][32] are intriguing aspects of the MBH reaction, and recent DFT studies have begun to provide useful mechanistic insights [33][34][35].Scheme 1 Morita-Baylis-Hillman (MBH) reaction. EWG: electronwithdrawing group.A few examples of dimerization reactions have been reported, but they require a catalyst [36][37][38][39], or high temperature [39], or high pressure [40]. We report the unusual case of a self-promoted dimerization of a triarylphosphine-substituted vinylphenyl-ketone 1, which we have been exploring as a ligand in Pd-catalyzed reactions [41][42][43].The dimerization of 1 (Scheme 2) occurs under ambient conditions in CH 2 Cl 2 /MeOH mixtures, requiring no additives, yielding dimer 2 in ca. 80% isolated yield. In situ NMR experiments and DFT calculations provide preliminary insight into the mechanism, including reaction order and solvent effects.Initially, we used different solvent combinations (CH 2 Cl 2 /hexane, THF/hexane, and CH 2 Cl 2 /MeOH) to grow crystals of 1. We obtained crystals of 1 (Figure 1 (a)) from CH 2 Cl 2 /hexane and THF/hexane, but were surprised to ob-

A Remarkable cis‐ and trans‐Spanning Dibenzylidene Acetone Diphosphine Chelating Ligand (dbaphos)

“…The other ligand bond lengths (CO, CC and CP) are within error of those in cis ‐[PtCl 2 ( 1 )]. It is of particularly note that the Morita–Bayliss–Hillman dimer diphosphine derived from the Lei ligand forms a similar trans‐ Pd II complex 34…”

“…It is of particularly note that the Morita-Bayliss-Hillman dimer diphosphine derived from the Lei ligand forms a similar trans-Pd II complex. [34] Two products were formed in an approximate 95:5 ratio (in quantitative conversion). A similar outcome was noted in [D 6 ]benzene (ca.…”