Takai olefination

Takai olefination in organic chemistry describes the organic reaction of an aldehyde with a diorganochromium compound to form an alkene. In the original 1986 publication[1] the aldehyde is benzaldehyde and the organochromium species is generated from iodoform or bromoform and an excess of chromium(II) chloride. The reaction product is a vinyl halide. The main selling point is the E-configuration of the double bond. According to the principal investigator Kazuhiko Takai, existing alternatives such as the Wittig reaction only yield mixtures.

Takai olefination
Named after Kazuhiko Takai
Reaction type Carbon-carbon bond forming reaction

In the reaction mechanism proposed by Takai, chromium(II) is oxidized to chromium(III) eliminating two equivalents of a halide. The geminal carbodianion complex thus formed (determined as [Cr2Cl4(CHI)(THF)4])[2][3] reacts with the aldehyde in a 1,2-addition along one of the carbon to chromium bonds and in the next step both chromium bearing groups engage in an elimination reaction. In newman projection it can be seen how the steric bulks of chromium groups and the steric bulks of the alkyl and halogen groups drive this reaction towards anti elimination.[4]

History of the reaction

Kazuhiko Takai is a professor of applied chemistry at Okayama University and is the recipient of the 2013 Chemical Society of Japan Award.[1][5] He primarily studies the use catalytic metals in synthesis reactions. He studied at Kyoto University and the University of California, Berkeley. The Takai olefination reaction was first described in a 1986 paper in the Journal of the American Chemical Society. Written by Kazuhiko Takai, Kenji Nitta, and Kiitiro Utimoto, the paper discusses the limitations of existing reagents, such as the Wittig reagent, in creating solely E isomers.[6][1]   Nitta, a graduate student working in the Utimoto group, carried out the reaction.

Similar olefination reactions have been performed, using a variety of reagents such as zinc and lead chloride;[7] however, these olefination reactions often lead to the formation of McMurry diols, not the methylenation or alkylidenation of aldehydes.[8] To circumvent this issue, Takai researched the potential of chromium (II) salts.

The reaction primarily employs the use of aldehydes, but ketones may be used.  However, ketones do not react as well as aldehydes; thus, for a compound with both aldehyde and ketone groups, the reaction can target just the aldehyde group and leave the ketone group intact.[1]

aldehyde specificity

The drawbacks to the reaction include the fact that stoichiometrically, 4 equivalents of chromium chloride must be used, since there is a reduction of two halogen atoms.[3] Ways to limit the amount of chromium chloride exist, namely by utilization of zinc equivalent,[9] but this method remains unpopular.

Takai–Utimoto olefination

In a second publication the scope of the reaction was extended to diorganochromium intermediates bearing alkyl groups instead of halogens:[10]

gollark: (note: I like Linux and this is a joke, do not potato me)
gollark: What do Linux users do to change a lightbulb?First, a user creates a bug report, only for it to be closed with "could not reproduce" as the developers got to it in the day. Eventually, some nights later, someone realizes that it is actually a problem, and decides to start work on a fix, soliciting the help of other people.Debates soon break out on the architecture of the new lightbulb - should they replace it with an incandescent bulb (since the bulb which broke was one of those), try and upgrade it to a halogen or LED bulb, which are technically superior if more complex. or go to a simpler and perhaps more reliable solution such as a fire?While an LED bulb is decided on, they eventually, after yet more debate, deem off-the-shelf bulbs unsuitable, and decide to make their own using commercially available LED modules. However, some of the group working on this are unhappy with this, and splinter off, trying to set up their own open semiconductor production operation to produce the LEDs.Despite delays introduced by feature creep, as it was decided halfway through to also add RGB capability and wireless control, the main group still manages to produce an early alpha, and tests it as a replacement for the original bulb. Unfortunately it stops working after a few days of use, and debugging of the system suggests that the problem is because of their power supply - the bulb needs complex, expensive, and somewhat easily damaged circuitry to convert the mains AC power into DC suitable for the LEDs, and they got that bit a bit wrong.So they decide to launch their own power grid and lighting fixture standard, which is, although incompatible with every other device, technically superior, and integrates high-speed networking so they can improve the control hardware. Having completely retrofitted the house the original lightbulb failed in and put all their designs and code up on GitHub, they deem the project a success, and after only a year!
gollark: Minetest is already a thing.
gollark: It really isn't.
gollark: Most people of my generation just use popular social media apps on a locked down phone of some sort and may not know what a "file" or "terminal" or "potatOS" is.

References
  1. Takai, K.; Nitta, K.; Utimoto, K. (1986). "Simple and selective method for RCHO → (E)-RCH==CHX conversion by means of a CHX3–CrCL2 system". Journal of the American Chemical Society. 108 (23): 7408–7410. doi:10.1021/ja00283a046.
  2. Werner, Daniel; Anwander, Reiner (28 September 2018). "Unveiling the Takai Olefination Reagent via Tris(tert-butoxy)siloxy Variants". Journal of the American Chemical Society. 140 (43): 14334–14341. doi:10.1021/jacs.8b08739. ISSN 0002-7863. PMID 30213182.
  3. Murai, Masahito; Taniguchi, Ryuji; Hosokawa, Naoki; Nishida, Yusuke; Mimachi, Hiroko; Oshiki, Toshiyuki; Takai, Kazuhiko (2017). "Structural Characterization and Unique Catalytic Performance of Silyl-Group-Substituted Geminal Dichromiomethane Complexes Stabilized with a Diamine Ligand". Journal of the American Chemical Society. 139 (37): 13184–13192. doi:10.1021/jacs.7b07487. PMID 28814078.
  4. Kürti, László; Czakó, Barbara (2005). Strategic Applications of Named Reactions in Organic Synthesis. Burlington; San Diego; London: Elsevier Academic Press. ISBN 978-0-12-369483-6.
  5. "Development of Novel Synthetic Organic Reactions by the Use of Group 4-7 Metals". The Chemical Society of Japan. Retrieved 2020-04-30.
  6. achem.okayama-u.ac.jp http://achem.okayama-u.ac.jp/omc/cv-takai-e.html. Retrieved 2020-04-13.
  7. Okazoe, Takashi; Takai, Kazuhiko; Oshima, Koichiro; Utimoto, Kiitiro (1987). "Alkylidenation of ester carbonyl groups by means of a reagent derived from RCHBr2, Zn, TiCl4, and TMEDA. Stereoselective preparation of (Z)-alkenyl ethers". The Journal of Organic Chemistry. 52 (19): 4410–4412. doi:10.1021/jo00228a055.
  8. Mukaiyama, Teruaki; Sato, Toshio; Hanna, Junichi (1973). "Reductive coupling of carbonyl compounds to pinacols and olefins by using TiCl4 and Zn". Chemistry Letters. 2 (10): 1041–1044. doi:10.1246/cl.1973.1041.
  9. Takai, Kazuhiko; Ichiguchi, Tetsuya; Hikasa, Shintaro (1999). "A Practical Transformation of Aldehydes into (E)-Iodoalkenes with Geminal Dichromium Reagents". Synlett. 1999 (8): 1268–1270. doi:10.1055/s-1999-2829.
  10. Okazoe, T.; Takai, Kazuhiko; Utimoto, K. (1987). "(E)-Selective olefination of aldehydes by means of gem-dichromium reagents derived by reduction of gem-diiodoalkanes with chromium(II) chloride". Journal of the American Chemical Society. 109 (3): 951–953. doi:10.1021/ja00237a081.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.