Chirality Transfer during the [2,3]-sila-Wittig Rearrangement and Cyclopropanation Reaction of Optically Active [(<i>s</i><i>ec</i>-Allyloxy)silyl]lithiums

Kawachi, Atsushi; Maeda, Hirofumi; Nakamura, Hiroshi; Doi, and Noriyuki; Tamao, Kohei

doi:10.1021/ja003749i

Cited by 23 publications

(28 citation statements)

References 12 publications

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“…When the hydroxy groups were protected as silyl ethers (TBDPS or TBDMS) (Table 1, entries 2, 3, and 6) or as an ester (Table 1, entry 5), satisfactory yields were obtained regardless of the position of the protected hydroxy group relative to the triple bond. In all cases, the Co 2 (CO) 6 bis-homopropargylic alcohols were satisfactorily decomplexed from the metal in the standard manner.…”

Section: Resultsmentioning

confidence: 94%

“…Antecedents: We have previously reported on novel stereoselective procedures for obtaining enantiomerically enriched products based on the Nicholas reaction that involve trapping of the carbocation generated by acid treatment of a chiral Co 2 (CO) 6 -complexed secondary propargylic alcohol with nucleophiles (Scheme 1). In both the intra-and intermolecular methodologies, the stereochemistry at the newly created stereocenter can be controlled by the existing substituents on the linear precursors.…”

Section: Resultsmentioning

confidence: 99%

“…[10] In addition, intramolecular hydrogen transfer is the key step in stereoselective processes such as the reduction of b-hydroxy ketones, [11] the aldol-Tishchenko reaction, [12] and some intramolecular ionic hydrogenations. [13] In the present work, we disclose full details of our results concerning complete chirality transfer in stereoselective intramolecular propargylic reduction in g-benzyl-protected Co 2 (CO) 6 -a,g-acetylenic diols, in which the chirality was introduced by way of an enantioselective Katsuki-Sharpless epoxidation. [14] The present study also demonstrates that the chiral integrity of the starting asymmetric center is preserved during the hydrogen transfer from the benzylic position.…”

Section: Introductionmentioning

confidence: 99%

“…[5] Chirality transfer during [2,3]-sila-Wittig rearrangements allows the stereoselective formation of SiÀC bonds. [6] In the literature, very efficient chirality transfers in acyclic systems have also been achieved from chiral heteroatoms to carbon derivatives, [7] and in chiral metal complexes, [8] palladium(0)-promoted intra-and intermolecular allylation reactions, [9] and [3,3]-sigmatropic rearrangements of allylic acetates catalyzed by palladium(ii). [10] In addition, intramolecular hydrogen transfer is the key step in stereoselective processes such as the reduction of b-hydroxy ketones, [11] the aldol-Tishchenko reaction, [12] and some intramolecular ionic hydrogenations.…”

Section: Introductionmentioning

confidence: 99%

“…Treatment of g-benzyl-protected Co 2 (CO) 6 -a,gacetylenic diols with BF 3 ·OEt 2 provides bis-homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range of functionalities, and provides good yields.…”

Section: Introductionmentioning

confidence: 99%

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[1,3]‐Transfer of Chirality during the Nicholas Reaction in γ‐Benzyloxy Propargylic Alcohols

Díaz

Ramírez

Martı́n

2006

Chemistry A European J

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A highly regio- and stereoselective intramolecular [1,5]-hydrogen-transfer process is described. Treatment of gamma-benzyl-protected Co2(CO)6-alpha,gamma-acetylenic diols with BF3 x OEt2 provides bis-homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range of functionalities, and provides good yields. When the ether group is located at a stereochemically defined carbon atom, the rearrangement occurs with high stereoselectivity, transferring the chirality of the carbinol center to the newly created stereocenter. The cleavage of the benzyloxy group is totally regioselective when additional benzyl ethers are present. The scope and limitations of this novel process in densely substituted substrates are evaluated, and possible competitive reactions and/or stereochemical influences are also described. A mechanism based on a highly ordered chair-like transition state substantiated by a theoretical study is also included.

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Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

[1,3]‐Transfer of Chirality during the Nicholas Reaction in γ‐Benzyloxy Propargylic Alcohols

Díaz

Ramírez

Martı́n

2006

Chemistry A European J

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[2,3]‐Wittig Rearrangement

2010

Comprehensive Organic Name Reactions and Reagents

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This reaction is a highly regioselective [2,3]‐sigmatropic rearrangement of the conjugate bases of allylic ethers (or benzylic ethers) to alcohols with concomitant C‐C bond formation. Therefore, this type of anionic [2,3]‐sigmatropic rearrangement is generally known as the [2,3]‐Wittig rearrangement. This rearrangement has been extended to α‐alkoxystannes and is referred to as the Still–Wittig [2,3]‐sigmatropic rearrangement. Analogously, the rearrangement of silyl anion from a silyl allylic ether is termed as the siloxy ‐[2,3] Wittig rearrangement and the rearrangement of an allylic amine in the presence of a strong base is called the aza ‐2,3‐Wittig rearrangement. The driving force for this rearrangement is probably the conversion of a moderately stabilized carbanion to a more stable alkoxide. It has been proposed that the breaking C‐O bond and the forming C‐C bond in the transition state are almost eclipsed, and the steric effect and electronic interaction at this point result in a high stereoselectivity. All the mechanistic features of the reaction have been discussed and it has been found that the tertiary bis ‐allyl ethers do not undergo the [2,3]‐Wittig rearrangement when treated with butyl lithium, but proceeds readily when treated with the combination of t ‐BuOK and t ‐BuLi. For the tertiary bis ‐allyl ether derived from (+)‐camphor, the rearrangement occurs via an endo ‐transition state to afford products of R ‐configuration. On the other hand, the substituent at either α‐ or γ‐position of the allylic moiety will depress the lithiation. In the case of 3‐furylmethyl ethers, the [2,3]‐Wittig rearrangement is indeed competed with [1,2]‐Wittig rearrangement, and the actual outcome depends on the bases applied. Overall, the [2,3]‐Wittig rearrangement is very common and widely used in organic synthesis.

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