Takai reaction

Stereoselective conversion of an aldehyde to the corresponding is-vinyl iodide using CHI3 and CrCl2. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 252, Springer-Verlag Berlin Heidelberg 2009 

Legrand, F. Archambaud, S. CoUet, S. Aphecetche-Julienne, K. Guingant, A. Evain, M. Synlett 2008, 389-393. 

The Tebbe s reagent, i-chlorobis(cyclopentadienyl)(dimethylaluminium)-g-methylenetitanium, transforms a carbonyl compound to the corresponding exoolefin. 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 271, Springer International Publishing Switzerland 2014 

Utimoto, K. J. Am. Chem. Soc. 1986, 108, 7408-7410. Kazuhiko Takai was a professor at Kyoto University. 

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The Takai Reaction provides the same transformation, but arrives at the E- configuration rather than... 

The first step is a Takai reaction.4 Geminal dihalide 12 is presumably converted in the presence of ehromium(H) chloride into the di-chromium complex 13, which reacts with aldehyde 5 to give product 14. 

This method is well-suited to preparing tram double bonds from aldehydes and geminal dihalides. The Takai reaction leads to FJ7 se-lcctivities >90 10. often even 99 1 (for further details see Chapter 13). 

A trimethylsilyl group in compound 6 serves as a dummy substituent in order to control the regiochemistry of the allylic alkylation reaction. Oppolzer added the necessary vinylsilane structural element with a Takai reaction. 

The stability of the u,p-iinsaturated lactone here is noteworthy, because the compound proves unreactive not only under the conditions of the Takai reaction but also during hydrogenation. Furthermore, Hoye does not mention any translactonization to the alcohol at C-4... 

We later published an improved synthesis of tonkinecin because of the low yield of the coupling reaction between 11 and 12 (only 30% previously) in a previous study. One major reason is that the vinyl iodide 12 was not stable enough to survive the basic reaction conditions. An alternative for the synthesis of right-side segment was then designed, in which the vinyl iodide functionality was introduced in the last step to avoid those basic conditions (Scheme 10-7). The Wittig reaction of aldehyde 15 with 16 and subsequent hydrogenation afforded ester 17, which was converted to lactone 18 by aldol reaction with lactal followed by acid treatment and [(-elimination. Selective deprotection, Dess-Martin oxidation, and Takai reaction (to introduce the vinyl iodide) afforded the precursor 19. Similar treatments of 19 with 14, as well as subsequent intermediates as described previously, finally provided tonkinecin. 

Auge, J., Boucard, V., Gil, R., Lubin-Germain, N., Picard, J., Uziel, J. An alternative procedure in the Takai reaction using chromium(lll) chloride hexahydrate as a convenient source of chromium(ll). Synth. Commun. 2003, 33, 3733-3739. 

Takai reaction, 205 Target-Oriented Synthesis (TOS), 355 TBAF (tetra-n-butylammonium fluoride), 57 TBAF, 31, 125, 198, 219,229,254,259,372 TBSOTf, 123, 198 TCFl, 358... 

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