Takai olefination

Within the context of total synthesis, the application of CM to a one-pot sequential protocol has the potential to dramatically simplify the preparation of complex natural products. Trost and co-workers recently demonstrated an elegant example of this, wherein a one-pot CM-Takai olefination reaction was used for the preparation of the antitumor agent callipeltoside A and various analogs (Scheme 21). By using a three-step, two-pot sequence employing this protocol, the synthetic route toward these compounds was shortened by five steps and olefin stereoselectivity was increased (4 1 to >8 1 E/Z) relative to previous syntheses employing a classical Emmons-Wadsworth-Horner approach. 

This aldehyde intermediate was then olefinated using the Takai olefination.29 This step was also attempted using the Wittig olefination, but the basic conditions lead to retro-Michael side reactions, hence resulting in low yields. The Takai olefination avoids the use of basic conditions and produced 29 and 30 in good yields. 

The Takai olefination [15] of 29 belongs to the lower-yielding steps in the synthesis by Nicolaou et al. (57%). Coupling with the Boc-protected piperazic acid derivative 30 gives the bis-iodovinyl compound 31, which is further elongated to 33 at the less hindered /i-NH... 

The reagents of the third step are also known as the Takai olefination conditions. Which functionality of the modified molecule reacts ... 

DDQ is a standard reagent for /7 /ra-methoxybenzyl (PMB) deprotection. The resulting free hydroxyl group is then oxidized to the corresponding aldehyde, which undergoes a subsequent Takai olefination. 

The diastereoselective MesAI-mediated intramolecular Diels-Alder reaction, a highly ( )-selective Takai olefination and a Suzuki coupling were the key steps in the enantioselective total synthesis of (-)-equisetin by K. Shishido et al. It should be noted that the type of T-U olefination utilized allowed the preparation of functionalized heterosubstituted ( )-alkenes. 

This reaction is related to the Takai Olefination and Tebbe Olefination. 

The educts 72/77 are synthesized (a) from aUyl alcohols 71 by addition to methoxyallene and (b) from ethyl vinyl ether by metalation, addition of an aldehyde, acylation, and Takai olefination ( 75 —> 76). 

Vinylcarbonyl compounds are common precursors for the generation of conjugated dienes. Recently, transformations including Wittig or related reactions, Julia or Takai olefination reactions, have been used to access heterosubstituted 1,3-dienes. 

The Takai olefination process has been described to allow the efficient generation of hetero-bis-metallobuta-l,3-diene 249 (Scheme 97) [191]. This type of diene can then be involved in sequential StiUe/Suzuki-Miyaura coupling reactions. 

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