On the Constitutional Stability ofη1-Allylmetal Compounds

Hoffmann, Reinhard W.; Polachowski, André

doi:10.1002/(sici)1521-3765(19980904)4:9<1724::aid-chem1724>3.0.co;2-e

Cited by 20 publications

(24 citation statements)

References 22 publications

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“…We were unaware of any prior example of exploiting similar strategy with 2-lithio-1,3-dienes. While a related vinyl iodide have been employed in cross coupling strategy to form the diene motif present in amphidinolide B, 40 the organolithium strategy brought with its potential for metallotropic rearrangement 41 of 49 . We initially explored accessing this lithio species via a Shapiro process from the corresponding hydrazone 52 ; however, this approach led to rapid decomposition.…”

Section: Resultsmentioning

confidence: 99%

Exploiting Hidden Symmetry in Natural Products: Total Syntheses of Amphidinolides C and F

Mahapatra

Carter

2013

J. Am. Chem. Soc.

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The total synthesis of amphidinolide C and a second-generation synthesis of amphidinolide F have been accomplished through the use of a common intermediate to access both the C1-C8 and the C18-C25 sections. The development of a Ag-catalyzed cyclization of a propargyl benzoate diol is described to access both trans-tetrahydrofuran rings. The evolution of a Felkin-controlled 2-lithio-1,3-dienyl addition strategy to incorporate C9-C11 diene as well as C8 stereocenter is detailed. Key controlling aspects in the sulfone alkylation / oxidative desulfurization to join the major subunits, including the exploration of the optimum masking group for the C18 carbonyl motif, are discussed. A Trost asymmetric alkynylation and a stereoselective cuprate addition to an alkynoate have been developed for the rapid construction of the C26-C34 subunit. A Tamura/Vedejs olefination to introduce the C26 sidearm of amphidnolides C and F is employed. The late-stage incorporation of the C15, C18 diketone motif proved critical to the successful competition of the total syntheses.

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Section: Resultsmentioning

confidence: 99%

Exploiting Hidden Symmetry in Natural Products: Total Syntheses of Amphidinolides C and F

Mahapatra

Carter

2013

J. Am. Chem. Soc.

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“…It is known that the energy barrier for the 1,3-boratropic shift is rather higher in allylic boronates than in allylic boranes, and that most crotyl boronates are configurationally stable at 0Ϫ20°C. [4,16] We therefore carried out a series of experiments in which phenylmagnesium chloride was added to 10, and the reaction mixture was then equilibrated for different times at various temperature (equilibration conditions) in order to allow migration and possible boratropic rearrangement to take place. Lastly, cyclohexanecarboxaldehyde was added, and the reaction mixture was stirred for 24 h at 20°C and finally quenched (H 2 O 2 /NaOH), to give homoallylic alcohols 8a and/or 9a.…”

Section: Synthesis Of Homoallylic Alcoholsmentioning

confidence: 99%

Regio- and Stereoselective Synthesis of Homoallylic Alcohols Based on the Use of (3-Chloroprop-1-en-1-yl)boronates

Lombardo¹,

Morganti²,

Tozzi³

et al. 2002

Eur. J. Org. Chem.

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“…However, as the zinc homologation proceeds in the presence of the aldehyde and the highest diastereoselectivity is observed at low temperature (−40 °C, dr 90:10 whereas at −20 °C the ratio decreases to 66:33), the outcome of the reaction must be kinetically controlled and, therefore, the allylation reaction is faster than any haptotropic equilibrium. 16 …”

Section: Introductionmentioning

confidence: 99%

Axial Preferences in Allylation Reactions via the Zimmerman–Traxler Transition State

et al. 2013

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CONSPECTUS The reaction of substituted allylmetal on prostereogenic carbonyl compound can give rise to up to two racemic diastereomers (syn and anti). Classically, when anti selectivity was observed from pure E-isomers while the Z-isomers exhibit syn-selectivity, the empirical Zimmerman – Traxler model is used. In this model, chair-like transition states are predicted to dominate over boat-like arrangements and the incoming aldehyde alkyl (aryl) residue occupies a pseudo-equatorial rather than a pseudo-axial position to avoid potential 1,3-diaxial steric interactions. However, the stereochemical outcome of the reaction of γ,γ-disubstituted allylzinc species with carbonyl compounds reaction may be completely different as two gauche interactions are generated. Would the two gauche interactions present in the transition state where the aldehyde substituent occupies a pseudo-equatorial position be preferred to a transition state in which the same substituent of the aldehyde occupies a pseudoaxial position? In this study, we could show that reaction of γ,γ-disubstituted allylzinc species with carbonyl compounds proceeds through a chair-like transition state and the substituent of the incoming aldehyde residue prefers to occupy a pseudo-axial rather than into a pseudo-equatorial position to avoid these two gauche interactions. Our experimental results were supported by theoretical calculations on model systems. This new stereochemical outcome has been extended to the formation of α-alkoxyallylation of aldehydes through the formation of the rather uncommon (E)-γ,γ-disubstituted alkoxyallylzinc species. This method could also be used to transform aromatic ketones as well as α-alkoxyaldehydes and ketone into functionalized adducts in which three new carbon-carbon bonds and two to three stereogenic centers, including an all-carbon quaternary stereocenter, were created in an acyclic systems in a single-pot operation from simple alkynes. Increasing the size of substituents on the zinc atom decreases the diastereoselectivity since 1,3-diaxial interactions are now produced with the axial substituent.

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On the Constitutional Stability ofη1-Allylmetal Compounds

Cited by 20 publications

References 22 publications

Exploiting Hidden Symmetry in Natural Products: Total Syntheses of Amphidinolides C and F

Exploiting Hidden Symmetry in Natural Products: Total Syntheses of Amphidinolides C and F

Regio- and Stereoselective Synthesis of Homoallylic Alcohols Based on the Use of (3-Chloroprop-1-en-1-yl)boronates

Axial Preferences in Allylation Reactions via the Zimmerman–Traxler Transition State

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