Catalytic aldehyde and ketone alkenation

Although the Wittig reaction (section 4.3.1) and its modified versions provide highly effective and general methods for the aldehydes and ketones alkenation, there are several drawbacks in their use. To overcome these drawbacks, new methods which employ the transition metal complex reagents as catalysts have been developed. A variety of catalytic aldehyde alkenation reactions have been reported with Mo catalyst other metals such as Re, Ru, Rh and Fe are also established as useful catalysts. Very mild conditions are required for catalytic alkenation short reaction times and high selectivities are generally observed. 

Several aldehydes were converted to alkenes by the use of 10% of the catalyst Mo02(S2CNEt2) in the presence of triphenylphosphine and diazoacetate. Alkenes yields of up to 83% were reached at 80°C and the -isomers were the main products. In contrast to the reactivity pattern of the Wittig reaction, the aliphatic aldehydes are more reactive than the aromatic aldehydes and the presence of electron-donating group enhances the yields. 

The reaction of p-chlorobenzaldehyde with phenyldiazomethane in the presence of (MeOlsP and catalytic amounts of meso-tetraphenylporphyrin iron chloride (ClFeTPP) resulted in the formation of the corresponding alkenes with an /Z-selectivity of 86 14, but the yield was low (30%). When phenyldiazomethane is generated in situ from the corresponding potassium tosylhydrazone salt, the olefin yield increases to 92% with E/Z-selectivity of 97 3. Thus, high levels of -selectivity are obtained with semistabilized ylides by this method . This process is applied to a wide range of aldehydes and is practical as compared to standard Wittig reaction, and therefore finds applications in industry, o 

PTC (10 mol%), P(OMe)3 (1.2 equiv.) Alkene with high E-selectivity toluene, 40°C 

The efficiency of this new method has been demonstrated in the synthesis of the anticancer compound 4.110. The standard Wittig reaction gives low selectivity however, this method gave the desired compound with 97 3 /Z-selectivity. 

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