Takai olefination

What is Takai olefination?

The Takai olefination, also known as the Takai reaction, was first reported by Takai et al. in 1986 (Okayama University). It involves coupling aldehydes with geminal dihaloalkanes in the presence of chromous chloride to form olefins. Takai olefination is sometimes referred to as the Takai-Utimoto olefination, and the chromous chloride CrCl2 is called the Takai-Utimoto reagent.

Takai olefination - general reaction scheme - Takai reaction
Takai olefination

Takai olefination is performed under neutral conditions in THF, and is especially effective for producing olefins with base-labile functional groups. The resulting iodo-olefins can also be used for other couplings, such as the Stille cross coupling.

Takai olefination primarily produces terminal iodo-olefins in the trans-configuration, with a reported E/Z ratio varying from 4.3:1 to 20:1. The use of dioxane as a co-solvent can further enhance the stereoselectivity in favor of the trans-configuration, but it may also cause a sluggish reaction and decrease the yield.

The reaction rate and yield can be increased by mechanical agitation and the application of instantly prepared dry chromous chloride CrCl2. However, the Takai olefination may yield a lower amount of olefin when performed on a large scale.

References

Simple and selective method for aldehydes (RCHO) → (E)-haloalkenes (RCH:CHX) conversion by means of a haloform-chromous chloride system
K. Takai, K. Nitta, and K. Utimoto
Journal of the American Chemical Society 1986 108 (23), 7408-7410
DOI: 10.1021/ja00283a046

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