Cascade Resulting in the Reductive Ethynylation of Aldehydes: Dissection of Its Components

Lee, Dong-Joo

doi:10.1021/ja910825g

Cited by 13 publications

(3 citation statements)

References 32 publications

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“…Allene-alkyne isomerization ordinarily requires the use of very strong bases . In contrast to the usual processes, the isomerization of the allene of 6 into the corresponding alkyne is promoted by a weak base as acetonitrile.…”

Section: Resultsmentioning

confidence: 99%

Osmium-Acyl Decarbonylation Promoted by Tp-Mediated Allenylidene Abstraction: A New Role of the Tp Ligand

et al. 2014

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Phenylacetylene and 1,1-diphenyl-2-propyn-1-ol displace the pyridyl and ethylene ligands of OsTp{κ 1 -C[NC 5 H 3 Me]}(η 2 -CH 2 CH 2 )(P i Pr 3 ) (1) to afford the alkynyl-vinylidene derivatives OsTp(CCR)(CCHR)(P i Pr 3 ) (Tp = hydridotris(pyrazolyl)borate; R = Ph, (2), C(OH)Ph 2 (3)). Stirring of toluene solutions of 3 in the presence of neutral aluminum oxide initially produces the dehydration of the vinylidene ligand to give the alkynyl-allenylidene OsTp{CCC(OH)Ph 2 }(CCCPh 2 )(P i Pr 3 ) (4), which subsequently undergoes a Meyer-Schuster rearrangement to yield the acyl-allenylidene OsTp{C(O)CHCPh 2 }(CCCPh 2 )(P i Pr 3 ) (5). In toluene, at 60 °C, the B−H bond of the Tp ligand of 5 abstracts the allene from the osmium coordination sphere by means of a 1,1-hydroboration of the Os−C α double bond. As a result, the acyl decarbonylation takes place to form Os( Ph2CCCH Tp)(CHCPh 2 )(CO)(P i Pr 3 ) (6). In acetonitrile at 60 °C, the allene tautomerizes into the alkyne to afford Os( Ph2HCCC Tp)(CHCPh 2 )(CO)(P i Pr 3 ) ( 7). The abstraction modifies the reactivity of the system toward HBF 4 . Thus, while the protonation of 5 leads to the alkylidyne [OsTp{C(O)CHCPh 2 }( CCHCPh 2 )(P i Pr 3 )]BF 4 (8), the protonation of 6 and 7 gives the alkylidenes [Os( Ph2CCCH Tp)(CHCHPh 2 )(CO)-(P i Pr 3 )]BF 4 ( 9) and [Os( Ph2HCCC Tp)(CHCHPh 2 )(CO)(P i Pr 3 )]BF 4 (10). Both 9 and 10 are unstable in solution. In dichloromethane, at room temperature, they evolve into the corresponding olefin derivatives [Os( Ph2CCCH Tp)(η 2 -CH 2  CPh 2 )(CO)(P i Pr 3 )]BF 4 (11) and [Os( Ph2HCCC Tp)(η 2 -CH 2 CPh 2 )(CO)(P i Pr 3 )]BF 4 (12) by means of a C β ,C α -hydrogen shift on the alkylidene ligand.

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Section: Resultsmentioning

confidence: 99%

Osmium-Acyl Decarbonylation Promoted by Tp-Mediated Allenylidene Abstraction: A New Role of the Tp Ligand

et al. 2014

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“…Danishefsky et al found that bis-trimethylsilylvinyl alcohol 74 could be deprotonated with n-BuLi and then treated with KO t Bu to effect transformation to the corresponding allene 76 (Scheme 19b). [40] Mechanistically, a sequence involving transmetalation, Brook rearrangement and elimination was proposed to account for this result. The majority of silyl allenes in this study were not isolated, but were isomerized directly to the corresponding alkynes.…”

Section: Scheme 18 Challenging Elimination In Peterson Allenylationmentioning

confidence: 99%

Synthesis of Allenes by 1,2-Elimination

Armstrong

2020

COC

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Allenes represent an extremely important class of organic molecules, which, as a result of their twisted orthogonal π-systems can possess axial chirality. A wide array of methods for allene synthesis have been reported, such as the substitution of propargylic electrophiles, isomerization of alkynes and sigmatropic rearrangement. An alternative approach for the synthesis of allenes is 1,2-elimination of an appropriately substituted precursor. This mini-review highlights recent examples of 1,2-elimination processes, which target allenes including both polar and radical processes. The main focus is upon how control over the stereospecificity (e.g. syn- or anti-) of the 1,2-elimination process can enable the synthesis of enantioenriched axially chiral allenes. Recent developments in this field are presented including both enantiospecific and catalytic asymmetric methods.

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“…Afterward, D undergoes migratory insertion to form E , which can be converted into allenyne 6′ via protonation or [5]cumulene 4 through 1,3-elimination. Finally, 6′ undergoes a base-assisted proton transfer (BAPT) 5 c ,14 to give the 1,3-diyne product 6 (see ESI† for details), while 4 undergoes the 1,3-H shift twice to form more stable 1-en-3,5-diyne 2 . As shown in deuterium-labelling experiments, the intramolecular 1,3-H shift is also accompanied by intermolecular BAPT.…”

mentioning

confidence: 99%