the benzyl group of the phosphorus atom

The Wittig reaction of benzyltriphenylphosphonium salt with benzaldehyde in organic solvent/water (NaOH) biphasic medium was studied, focusing on the effects of substituents and organic solvents. Substituents selected for study included CH3, F, Cl, Br, CH3O, NO2, and CF3. Organic solvents

The Wittig reaction of benzyltriphenylphosphonium salt with benzaldehyde in organic solvent/water (NaOH) biphasic medium was studied, focusing on the effects of substituents and organic solvents. Substituents selected for study included CH3, F, Cl, Br, CH3O, NO2, and CF3. Organic solvents include polar solvents (CHCl3 and CH2Cl2) and nonpolar solvents (n-C6H14, C6H6 and CCl4). It was found that the stirring rate was not critical and the reaction of benzylidenetriphenylphosphorane and benzaldehyde in the organic phase was the decisive step in determining the Z/E ratio of the product stilbene. In general, polar solvents exhibit more favorable Z-selectivities. By exchanging the substituents on the benzyl group of the phosphorus atom and the benzyltriphenylphosphonium chloride  group of the aromatic aldehyde, the Z/E ratio of the product stilbene can be significantly changed. Ortho-substituted benzaldehydes with heteroatom substituents show a significant enhancement in Z-selectivity compared to meta- and para-substituted benzaldehydes and ortho-substituted benzaldehydes, the effectiveness of the substituents The order is CF3(Cl, Br )CH3OFNO2. A cooperative asynchronous cycloaddition mechanism involving a four-center transition state is proposed to operate in these systems.
The Wittig reaction is one of the most important and versatile reactions in organic chemistry for the synthesis of alkenes with well-defined double bond positions. Since its discovery in the early 1950s1,2, the Wittig reaction has been extensively studied both theoretically and synthetically3,4,5,6,7,8,9,10,11,12 and because of its simplicity And is highly recognized, efficient and versatile. The prototypical Wittig reaction involves the reaction of a phosphonium ylide with an aldehyde or a ketone, as shown in reaction (R1).



Stereoselectivity is highly dependent on the substituents bonded to the ylate carbon and phosphorus atoms, as well as the precise reaction conditions. According to their general reactivity, phosphorus ylides are classified into three classes, namely, non-stabilized ylides, semi-stabilized ylides, and stable ylides. The Wittig reaction has been shown to preferentially produce E alkenes for stable ylides with strongly conjugated substituents (e.g. COOMe or CN); a mixture of semi-stabilized yliden Z and E olefins; non-stabilized ylides, mainly antithermodynamic Z olefins, lack such conjugated functional groups (e.g., alkyl groups). Most studies of the Wittig reaction are performed homogeneously in organic solvents such as THF, C6H6, CCl4, CHCl3, DMF, and MeOH.


iudjakd da

82 Blog posts

Comments