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烯化反应 [C-C成键反应]

 Carbonyl olefination is one of the most fundamental conversions in organic synthesis and a variety of synthetic methods have been developed. Particularly, synthetic methods focused on the chemical properties of heavy-atoms such as phosphorus, silicon and sulfur atoms had long been studied. One of them, the Wittig reaction is the representative carbonyl olefination reaction. Other similar reactions, the silicon-mediated Peterson olefination and two sulfur-based “Julia” carbonyl olefinations named the Julia-Lythgoe olefination and the Julia‐Kocienski olefination are also useful olefinating methods. Among them, as the Wittig and Horner-Emmons reactions are the most general carbonyl olefinations, a number of improved synthetic applications have also been investigated. Some of them allow providing easer work-up procedures and increasing the stereoselectivity of the double bond of olefins. They are even now widely used for this transformation.
 In the 1990s, organotitanium species-promoted carbonyl olefinations had been studied and various successful methods were reported. The biggest advantage of the use of organotitanium species in carbonyl olefination is that not only aldehydes and ketones, but also esters and lactones can be transformed to the corresponding olefins. Furthermore, the basicities of the organotitanium species are weaker compared to that of Wittig type bases and these chemical properties enable easily enolizable substrates to be used in carbonyl olefinations and to produce the desired olefins with high yields.