The regiospecific lithiation of aromatic acetals

Plaumann, Heinz; Keay, Brian A.; Rodrigo, R.

doi:10.1016/s0040-4039(01)86750-2

Cited by 39 publications

(11 citation statements)

References 4 publications

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“…However, direct application of any of these strategies toward the appropriately substituted 4‐oxidoisoquinolinium 89 was not obvious, and so an alternative strategy was pursued based on a late‐stage cycloaromatization–condensation event, similar to that in the second phase of the classic aza‐Achmatowicz reaction. Preparation of the 4‐oxidoisoquinolinium betaine commenced with commercially available 4‐methoxybenzaldehyde dimethyl acetal ( 91 , Scheme ) in which directed ortho ‐lithiation101 and acylation with α‐chloro‐ N ‐methoxy‐ N ‐methylacetamide provided the chloroacetophenone 92 (52 %). Nucleophilic substitution of the chloride in 92 with NaN 3 proceeded smoothly (95 %), allowing for subsequent acid‐catalyzed acetal isomerization in MeOH to produce the bicyclic diacetal 93 (99 %) as a 3:…”

Section: Resultsmentioning

confidence: 99%

Asymmetric Synthetic Access to the Hetisine Alkaloids: Total Synthesis of (+)‐Nominine

Peese

Gin

2008

Chemistry A European J

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A dual cycloaddition strategy for the synthesis of the hetisine alkaloids has been developed, illustrated by a concise asymmetric total synthesis of (+)-nominine (7). The approach relies on an early-stage intramolecular 1,3-dipolar cycloaddition of a 4-oxido-isoquinolinium betaine dipole with an enenitrile dipolarophile. Subsequent late-stage pyrrolidine-induced dienamine isomerization/DielsAlder cascade allows for rapid construction of the carbon-nitrogen polycyclic skeleton within this class of C 20 -diterpenoid alkaloids.

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Section: Resultsmentioning

confidence: 99%

Asymmetric Synthetic Access to the Hetisine Alkaloids: Total Synthesis of (+)‐Nominine

Peese

Gin

2008

Chemistry A European J

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“…Alternatively, direct ortho-deprotonation (8) of aromatic acetals, followed by treatment of the ensuing ord~o-lithio species with nonenolizable aldehydes, provides a series of contiguously substituted hydroxyacetals { A~-A S ) . A major shortcoming of these preparations is that the aryl lithium species is readily protonated by enolizable aldehydes or ketones, thus precluding the use of most aliphatic aldehydes and limiting the R' substituent to H or aryl.…”

Section: Preparatiorl Of Hydrosyacetals (A)mentioning

confidence: 99%

Hydroxyacetals, phthalans, and isobenzofurans therefrom

Keay¹,

Plaumann²,

Rajapaksa³

et al. 1983

Can. J. Chem.

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A general method for the generation of isobenzofuran intermediates is described. Lithiated aromatic acetals are converted to hydroxyacetals (A) which may be cyclized to isobenzofurans by mild acid treatment through the 1-hydroxyphthalans (B). The isobenzofurans generated insitu are trapped by a variety of dienophiles to provide the expected oxo-bicyclo adducts (C). The mass and 1Hmr spectra of B and C are discussed.

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“…Steric constraints would lead to the suggestion of 1,1Ј and 3,3Ј substitution but there is evidence for regioselective lithiation of substituted ferrocenes and simple π arene systems with N-, Por O-containing substituents. [6][7][8] This has been attributed to an intramolecular co-ordination between the lithium atom and the lone pair of electrons on the substituent. These points indicate the possibility of substituting all the cyclopentadienyl protons to form deca-substituted (methylthio)ferrocene and thus the analogous 'superferrocenophanes'.…”

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confidence: 99%