422. Experiments towards the synthesis of corrins. Part I. The preparation and reactions of some Δ<sup>1</sup>-pyrrolines. A novel proline synthesis

Bonnett, Raymond; Clark, V. M.; Giddey, André; Todd, A. R.

doi:10.1039/jr9590002087

Cited by 69 publications

(30 citation statements)

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“…Spectroscopic data for these adducts compared directly with those for 4a and 5a and X-ray crystallographic analyses were obtained for 5b, 4c-e. 10 Monoactivated alkene dipolarophiles also reacted and, although the yields were low to moderate, ylid 3 nonetheless exhibits a greater reactivity compared to the corresponding aldehyde-derived ylids which react very poorly, if at all, with monoactivated dipolarophiles. 5a-i Methyl acrylate and acrylonitrile afforded the corresponding endo-adducts 4e and 4f in 14% and 40% yields respectively as the sole cycloadducts and 1-chloroacrylonitrile afforded a roughly equal ratio of inseparable diastereomeric addition products 4g and 5g in 39% combined yield (Table in Scheme 2). Spectroscopic data were consistent with the regiochemistry and endo-stereochemistry for 4e-g and an X-ray crystallographic analysis confirmed the structure of 4e.…”

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confidence: 70%

An Acetone-derived Chiral Stabilised Azomethine Ylid: Synthesis of Enantiomerically Pure 5,5,-Dimethylproline Derivatives

Aldous¹,

Drew²,

Hamelin³

et al. 2001

Synlett

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The chiral stabilised azomethine ylid 3 generated in situ via Lewis acid catalysed condensation of (5S)-5-phenylmorpholin-2-one with 2,2-dimethoxypropane can be trapped diastereoselectively with singly and doubly activated dipolarophiles. The cycloadducts may be dismantled in one pot to furnish enantiomerically pure 5,5-dimethylproline derivatives.Key words: ketone-derived chiral stabilised azomethine ylid, 5,5-dimethylprolines, Lewis acid 5,5-Dimethylproline (dmP) 2 has been shown to induce a restrained cis-amide bond conformation when included in peptidic systems. The racemic material has been incorporated into the dipeptide Boc-L-Phe-DL-dmP-OMe which was shown to exist as 90% the cis-conformer. 3 More recently, enantiomerically pure L-dmP, obtained from the racemate by resolution, has been incorporated into Nacetylated tripeptides designed to mimic regions of RNase A which possess cis-proline peptide linkages. 4 In the case of the tripeptide Ac-Tyr-L-dmP-Asn, 100% cis-conformation could be achieved; whereas Ac-Asn-L-dmP-Tyr gave an equilibrium mixture in which the cis-conformer predominated. However, the lack of generality of the reported synthetic approaches to the parent 2,3 severely restricts scope for investigation in this area using functionalised analogues.With this in mind, we considered that our chiral azomethine ylid cycloaddition strategy for accessing enantiomerically pure prolines 5a-i could provide a convenient and general approach to enantiomerically pure 5,5-disubstituted prolines if it were possible to generate an ylid by condensation of a ketone with (5S)-5-phenylmorpholinone 1 (Scheme 1). However, to the best of our knowledge, the generation of ylids by condensing ketones with secondary amines has not been reported, indicating potential pitfalls to such a route.These fears were borne out by experience when attempts at condensing acetone with 1 under conditions which had previously been successful with aldehydes resulted in no reaction. Surveying a range of Brønsted and Lewis acid catalysts and a variety of increasingly forcing reaction conditions proved equally fruitless. Presumably the combination of reduced electrophilicity of the ketone and the increased steric hindrance associated with formation of the ketone-derived azomethine ylid is responsible for this lack of reactivity. We experienced no better fortune when replacing acetone with 2-methoxypropene under a wide variety of conditions, but when 1 was treated with 2,2-dimethoxypropane in refluxing THF in the presence of MgBr 2 ×Et 2 O we observed disappearance of starting material and the formation of a new product. This material was very labile but could be sufficiently purified to identify it as the adduct 2 (Scheme 2). 6Although isolation of 2 in satisfactory yields proved impossible, methoxymethylene analogues of 2 have been used by Williams 7 and ourselves 8 as a means of generating formaldehyde-derived azomethine ylids in situ. To our satisfaction, repeating this reaction in the presence of Nphenylmaleimide led to formation of two ...

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supporting

confidence: 70%

An Acetone-derived Chiral Stabilised Azomethine Ylid: Synthesis of Enantiomerically Pure 5,5,-Dimethylproline Derivatives

Aldous¹,

Drew²,

Hamelin³

et al. 2001

Synlett

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“…Conversely, the electron-withdrawing effect of the pyrroline unit (in the neutral form or even more so in the protonated form) increases the electrophilicity of the adjacent formyl group whereas the formyl group in the dipyrromethane is attached to an electron-rich pyrrole. The pyrroline unit is undoubtedly protonated under the reaction conditions; indeed, protonated 2-methylpyrrole 250 has p K a = −0.21 whereas protonated 2,4,4-trimethyl-Δ 1 -pyrroline 180 has p K a = 7.6.…”

Section: Development Of De Novo Syntheses Of Gem-dialkylchlorinsmentioning

confidence: 99%

De NovoSynthesis of Gem-Dialkyl Chlorophyll Analogues for Probing and Emulating Our Green World

2015

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Woodward reported his infamous synthesis of chlorin e 6 trimethyl ester, a known synthetic precursor to chlorophyll a. [59][60][61][62][63][64]124 The work was posited on a half-century of intensive studies by many investigators in tetrapyrrole chemistry and began a decade after the close of Fischer's lifetime of research 125−128 (which included an uncompleted synthetic program directed toward chlorophylls 15 ). Indeed, "he read all the umpteen papers on the chlorophylls written by Willstaẗter and Fischer, including the experimental parts." 129 The Woodward synthesis of chlorin e 6 trimethyl ester required 46 steps, of which 24 were spent on converting the sole precursor, Knorr's pyrrole, to the four pyrroles destined to form rings A−D; 7 additional steps accrued to obtain the dipyrromethanes that constitute the Eastern and Western halves (Scheme 13, the step numbers are identical to those shown in ref 64.). The first step formed the Knorr pyrrole (in several kg quantities), the next 24 steps were divided into four parallel paths, whereas the remaining 21 steps proceeded in linear fashion. Remarkable features of the synthesis include the directed intramolecular joining (via an imine) of the Eastern and Western halves (step 33), construction of the acrylate Scheme 10. Hydrogenation of a Porphyrin to Form a Chlorin Scheme 11. Representative meso-Tetraarylchlorins Scheme 12. Methyl Pyropheophorbide a

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“…Les differents pieges a radicaux sont prtparis suivant les mCthodes indiquCes dans la littkrature: DMPO (37)(38)(39) \CD, \CD, 420nm) dans les solvants utilis~s, ne donnent pas de signaux.…”

Section: Priparation R/es Pikges B Radicauxunclassified

Utilisation des pièges à radicaux en vue de mettre en évidence des intermédiaires dans la photolyse de complexes contenant une liaison Co^III—C

Maillard¹,

Giannotti²

1982

Can. J. Chem.

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Using the spin trapping technique with 5,5′-dimethyl 1-pyrroline N-oxide (DMPO), phenyl-N-tert-butyl nitrone (PBN), nitrosodurene (ND), and α-4-pyridyl 1-oxide N-tert-butl nitrone (4-POBN), or their mixtures, we have been able to detect two types of radicals, one is a hydrogen atom spin adduct and the other is the corresponding alkyl of the alkylcobaloximes, salens or cobalamines.By the use of selective deuteration and the preparation of the benzyl bis(diphenylglyoximato)-pyridinato cobaloxime, we have shown that the spin trapped hydrogen atom comes from the chelated hydrogen of the dimethylglyoximato anion of the equatorial ligand of CoIII complexes. Using a mixture of two spin traps gives rise to an esr spectrum containing, at the same time, the hydrogen atom and alkyl spin adducts.To explain such an efficient spin trapping reaction while the homolysis is in competition with a β-elimination process, it should be postulated that the photolysis of such compounds proceeds through a solvent cage environment. This hypothesis explains the strong influence of solvents on the nature of the free radicals trapped. Also the spin trap diffuses in the solvent cage, and is able to trap in a very efficient manner any free radicals occurring in the solvent cage. The excited CoIII complexes and the spin trap in the solvent cage behave like an exciplex, which could explain the spin trapping of the hydrogen atom.

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422. Experiments towards the synthesis of corrins. Part I. The preparation and reactions of some Δ¹-pyrrolines. A novel proline synthesis

Abstract: 2087 422. Experiments towards the Synthesis of Corrins. Part I. The A Novel Proline Preparation and Reactions of Some A1-Pyrrolines. Synthesis.

Cited by 69 publications

References 0 publications

An Acetone-derived Chiral Stabilised Azomethine Ylid: Synthesis of Enantiomerically Pure 5,5,-Dimethylproline Derivatives

An Acetone-derived Chiral Stabilised Azomethine Ylid: Synthesis of Enantiomerically Pure 5,5,-Dimethylproline Derivatives

De NovoSynthesis of Gem-Dialkyl Chlorophyll Analogues for Probing and Emulating Our Green World

Utilisation des pièges à radicaux en vue de mettre en évidence des intermédiaires dans la photolyse de complexes contenant une liaison Co^III—C

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422. Experiments towards the synthesis of corrins. Part I. The preparation and reactions of some Δ1-pyrrolines. A novel proline synthesis

Abstract: 2087 422. Experiments towards the Synthesis of Corrins. Part I. The A Novel Proline Preparation and Reactions of Some A1-Pyrrolines. Synthesis.

Cited by 69 publications

References 0 publications

An Acetone-derived Chiral Stabilised Azomethine Ylid: Synthesis of Enantiomerically Pure 5,5,-Dimethylproline Derivatives

An Acetone-derived Chiral Stabilised Azomethine Ylid: Synthesis of Enantiomerically Pure 5,5,-Dimethylproline Derivatives

De NovoSynthesis of Gem-Dialkyl Chlorophyll Analogues for Probing and Emulating Our Green World

Utilisation des pièges à radicaux en vue de mettre en évidence des intermédiaires dans la photolyse de complexes contenant une liaison CoIII—C

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422. Experiments towards the synthesis of corrins. Part I. The preparation and reactions of some Δ¹-pyrrolines. A novel proline synthesis

Utilisation des pièges à radicaux en vue de mettre en évidence des intermédiaires dans la photolyse de complexes contenant une liaison Co^III—C