Titration of alkyllithiums with a simple reagent to a blue endpoint

Burchat, Andrew; Chong, J. Michael; Nielsen, N.

doi:10.1016/s0022-328x(97)00143-5

Cited by 166 publications

(151 citation statements)

References 11 publications

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“…sBuLi was titrated from N-benzylbenzamide. [50] Reagents were obtained from Sigma Aldrich, TCI Europe and Johnson Matthey Chemicals Limited. Celite used for filtration was Celite 535, acquired from Sigma-Aldrich.…”

Section: Methodsmentioning

confidence: 99%

Synthesis of Chiral (Indol‐2‐yl)methanamines and Insight into the Stereochemistry Protecting Effects of the 9‐Phenyl‐9‐fluorenyl Protecting Group

et al. 2015

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(2015). Synthesis of chiral 2-indolyl methanamines and insight into the stereochemistry protecting effects of the 9-phenyl-9-fluorenyl protecting group. EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2015(17) Keywords: Asymmetric synthesis / Amino acids / Chiral pool / Protecting groups Tetrahydro-β-carbolines, a privileged structural feature in natural products and pharmaceutically active compounds, has been the cause for considerable research interest, spanning many decades. Herein is reported the synthesis of the structurally closely related compounds denoted as (indol-2-yl)methanamines, in 99 % ee using amino acid starting materials, coupled with a 9-phenyl-9-fluorenyl (Pf) protect-

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Section: Methodsmentioning

confidence: 99%

Synthesis of Chiral (Indol‐2‐yl)methanamines and Insight into the Stereochemistry Protecting Effects of the 9‐Phenyl‐9‐fluorenyl Protecting Group

et al. 2015

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“…n-Butyllithium and s-butyllithium were titrated against Nbenzylbenzamide before use. 25 Flash column chromatography was carried out using Fluka Chemie GmbH silica (220-440 mesh). Thin layer chromatography was carried out using Merck F 254 aluminium-backed silica plates.…”

Section: Methodsmentioning

confidence: 99%

Investigation of bispidines as the stoichiometric ligand in the two-ligand catalytic asymmetric deprotonation of N-boc pyrrolidine

Barker¹,

O’Brien²,

Campos³

2011

Arkivoc

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“…THF was dried by distillation from sodium/Ph 2 CO. Titration of the n-BuLi solutions was carried out with N-benzylbenzamide to a blue endpoint. 20) The NMR spectra were recorded on a Brucker Avance 300 MHz and Brucker Avance 400 MHz spectrometers in CDCl 3 , unless otherwise noted. Chemical shifts are given in ppm with TMS as the internal standard.…”

Section: Methodsmentioning

confidence: 99%

First Total Synthesis of Justicidone, a p-Quinone-Lignan Derivative from Justicia hyssopifolia

Boluda

López

Pérez

et al. 2005

CHEMICAL & PHARMACEUTICAL BULLETIN

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Justicidone (1), is a C-5, C-8 dioxo-lignan derivative isolated from Justicia hyssopifolia 2) (Acanthaceae), whose structure may be considered as having either para-naphthoquinone or lignan-derivative features. The interesting biological activity of lignans, [3][4][5] and orto-and para-quinones [6][7][8] could be perhaps improved if both types of compounds were included in one common structure. Due to the potential biological activity of justicidone and, on the other hand, that Justicia hyssopifolia could only render this compound in a few milligrams, then we became interested in the synthesis of this compound, that we report herein. Results and DiscussionThe proposed synthetic strategy, shown in Chart 1, involves the compound 9, which by oxidation, may lead to the synthetic objective 1. There is a variety of methods to synthesize lignans of the 1-arylnaphthalene skeleton.9-16) Nevertheless, it has been described, up to now, no natural lignan derivative of the 1-arylnaphthalene type which presents the 2,4,5-substitution pattern in the A ring. In reality, this type of substitution is not common in lignans, being magnoshinin, a dihydro-1-arylnaphthalene lignan derivative, the only compound of this type with such a substitution pattern described in the literature as a natural compound isolated from Magnolia salicifolia.17) This compound was efficiently synthesized by Yoshida et al. 18) and by Yvon et al. 19)We initiated the synthesis of justicidone (1) by preparing 2 from Piperonal (Chart 2). Treatment of 2 with n-butyllithium (n-BuLi) in tetrahydrofuran (THF) for an hour, followed by the addition of 2(5H)-furanone, gave rise to 3. The enolate derived from 3 by the reaction of this compound with lithium diisopropylamide (LDA) in THF was captured by 2,4,5-trimethoxybenzaldehyde which led to a diastereomeric mixture of compounds 4, which was separated, as it is described in the experimental part, into the diastereomers 4a and 4b. The protection of the mixture of 4 was removed by the reaction with HgO in Et 2 O-BF 3 , to give, as it was expected, a diastereomeric mixture of 5, which was also separated into 5a and 5b. Both compounds 5 and 6 in Chart 2 could lead directly to 9 by acidic treatment after protonation of the carbonyl oxygen and electrophilic substitution on the carbocation. Nevertheless, all attempts for the diastereomeric mixture 5 to be transformed into 9, failed and instead of 9 gave 6, which unexpectedly also resisted to give 9 in a more intense acidic treatment. It would be expected that a more reactive (less stable) carbocation could give the aromatic electrophilic substitution and cause closure of the ring, but not its aromatization, in an easier way. So, reduction of 6 with NaBH 4 gave 7, which by treatment with trifluoroacetic acid (TFA) in benzene gave 8. This last compound was aromatized by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to give 9. Oxidation of 9 with ceric ammonium nitrate (CAN) gave justicidone (1). On the other hand, oxidation of 8 with CAN gave also compound ...

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Titration of alkyllithiums with a simple reagent to a blue endpoint

Cited by 166 publications

References 11 publications

Synthesis of Chiral (Indol‐2‐yl)methanamines and Insight into the Stereochemistry Protecting Effects of the 9‐Phenyl‐9‐fluorenyl Protecting Group

Synthesis of Chiral (Indol‐2‐yl)methanamines and Insight into the Stereochemistry Protecting Effects of the 9‐Phenyl‐9‐fluorenyl Protecting Group

Investigation of bispidines as the stoichiometric ligand in the two-ligand catalytic asymmetric deprotonation of N-boc pyrrolidine

First Total Synthesis of Justicidone, a p-Quinone-Lignan Derivative from Justicia hyssopifolia

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