Chiral azo compounds: enantioselective synthesis and transformations into β-amino alcohols and α-amino acids with a quaternary stereocenter

Dietz, Friedrich R.; Prechter, Agnes; Gröger, Harald; Heinrich, Markus R.

doi:10.1016/j.tetlet.2010.11.137

Cited by 15 publications

(8 citation statements)

References 16 publications

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“…In a preliminary screening of enzymes, the widely used Candida antarctica lipase B (CAL-B) turned out to be a suitable biocatalyst for our purpose. 45 As shown in Scheme 8, the azo compound 32 (see also Scheme 5) was converted into the corresponding alcohol (R)-19 in 42% yield and 86% enantiomeric excess, albeit after a reaction time of seven days.…”

Section: Account Syn Lettmentioning

confidence: 99%

“…For reasons of solubility, it was necessary to use dichloromethane as a solvent, so the reaction was limited to activated alkenes that undergo sufficiently rapid addition of aryl radicals. 38 After a detailed study of the products formed from bisdiazene 44, acrylonitrile (45), and TEMPO (46), it became obvious that, under the reaction conditions used, the aryl radicals can combine directly with TEMPO to give the phenyloxy derivative 47. However, the desired Meerwein arylation products, such as 48, were also obtained in moderate to good yields, along with the TEMPO adduct 49.…”

Section: Carbooxygenationmentioning

confidence: 99%

“…96 In all these reactions, the formation of an aryl radical from the diazonium compound 74 was followed by an intramolecular addition or by cyclization to give a primary alkyl radical attached to a dihydrobenzofuran core. This primary alkyl radical could then be added to acrylonitrile (45) in the presence of TEMPO (46) to give the adduct 75, or could participate in vinylation or allylation reactions with alkenes 78 or 79 to give the benzofurans 76 and 77, respectively.…”

Section: Cascade Reactionsmentioning

confidence: 99%

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How the Structural Elucidation of the Natural Product Stephanosporin Led to New Developments in Aryl Radical and Medicinal Chemistry

Fehler

Heinrich

2015

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The intent of this account is to provide a focused overview of recent developments in aryl radical chemistry, especially extensions and applications of the Meerwein arylation and the Gomberg-Bachmann reaction. Although most of the reactions and methods described were discovered on the basis of earlier findings made by our group or logically depend on newly discovered reactivities or mechanistic principles, the rapid evolution of radical chemistry can nevertheless be traced back to the behavior of the natural product stephanosporin, which is capable of liberating 2-chloro-4-nitrophenol via an aryl radical intermediate.

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Section: Account Syn Lettmentioning

confidence: 99%

Section: Carbooxygenationmentioning

confidence: 99%

Section: Cascade Reactionsmentioning

confidence: 99%

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How the Structural Elucidation of the Natural Product Stephanosporin Led to New Developments in Aryl Radical and Medicinal Chemistry

Fehler

Heinrich

2015

Synlett

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“…6 So far, unfavorably, the access to azo compounds 6 in enantiomerically enriched form has been extremely limited due to the narrow substrate scope, long reaction times and high enzyme loading required for lipase-catalyzed kinetic resolutions. 11 In this communication, we now report recent advances leading to an efficient access to enantiomerically enriched azo acetates through lipase-catalyzed kinetic resolution.…”

mentioning

confidence: 99%

“…Due to the low conversions observed for azo acetates in the previously employed aqueous biphasic mixtures of methyl tertbutyl ether (MTBE) and water, 11 we first examined the hydrolysis of acetate 7a in a variety of non-dried organic solvents including acetonitrile, MTBE, methanol, n-hexane, dimethylformamide (DMF), acetone and tetrahydrofuran (THF) (Table 1, entries 1-8).…”

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confidence: 99%

Synthesis of (S)-(+)-cericlamine through lipase-catalyzed aminolysis of azo acetates

2012

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Copper‐Catalyzed Trifluoromethylation of Hydrazones Leading to the Formation of Quaternary α‐Trifluoromethyl Diazenes

2016

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The copper-catalyzed azomethine trifluoromethylation of ketone-derived hydrazones with To gni'sh ypervalent iodine(III)-CF 3 reagent is described. The reaction gives rise to quaternary a-trifluoromethyl diazenes under mild conditions andi sp roposed to proceed via ar adical process.The trifluoromethyl (CF 3 )g roup has gained extreme importance in the pharmaceutical and agrochemical industries owing to its unique ability to modulate physicochemical and biological properties of lead compounds in drug discovery. [1] For these reasons, intensiveresearchefforts have been recently devotedt ot he development of practical methods for direct and selectivei ncorporation of aC F 3 moiety into organic molecules.[2] In this area, creationo fC F 3 -containing quaternary stereocenters remains ah ighly desirable yet challenging task due to the steric congestion encountered duringt he CÀCF 3 bond formation.[3] While nucleophilic 1,2-additions of aC F 3 group across unsaturated moieties, including C=Oa nd C=Nb onds, have been widely exploited toward this goal, [4] quaternary stereogenicity arising from electrophilic and radical processes remains relativelyu nexplored. To date, achievements in this area have essentially concerned the synthesis of all-carbon quaternary a-CF 3 ketones and carboxylic esters through metal-catalyzed a-trifluoromethylation of carbonyl compounds, [5] or via their enol ether surrogates. [6,7] Diazenesa re important organic reagents commonly involved in aw idev ariety of reactions including cycloadditions [8] and radicalp rocesses.[9] Mainly used as dyes andp igmentsi nm any industry sectors, [10] they have also found application as azo prodrugs for bioactive amine delivery.[11] However,w hile synthetic methods for preparing azobenzenes (Ar-N=N-Ar) are now well-established, [12] the development of efficient processes targetinga liphatic diazenes remains challenging, partly due to their inherentt hermal and photoinstability.A saconsequence, very limited synthetic methodsa re availablef or preparing diazenes with an adjacent quaternary carbon stereocenter. These essentially rely on the diazenylation of carbonyl compounds, [13] silyl enol ethers, [14] and non-activated olefins [15] with arene diazonium salts (or aromatic triazenes)t oa fford the corresponding aryl(alkyl)diazenes(Ar-N=N-Alkyl).Currently,t here is no convenient methoda vailable to access a-trifluoromethyl diazenes.T his situation promptedu st od evelop as ynthetic procedure to preparet hesep otentially useful compounds directly from readily available hydrazone derivatives [16] and an electrophilics ource of CF 3 .I ndeed, we recently developed av ery mild procedure for CÀHt rifluoromethylation of N,N-disubstituted aldehyde-derived hydrazones by using To gni reagent 1 under copper catalysis (Scheme 1a). The radical/single electron transfer (SET)-initiated reactionw as proposed to follow an addition-elimination pathway involving the intermediate cationic species I that restored the hydrazone moiety upon protona bstraction.[17] We there...

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Chiral azo compounds: enantioselective synthesis and transformations into β-amino alcohols and α-amino acids with a quaternary stereocenter

Cited by 15 publications

References 16 publications

How the Structural Elucidation of the Natural Product Stephanosporin Led to New Developments in Aryl Radical and Medicinal Chemistry

How the Structural Elucidation of the Natural Product Stephanosporin Led to New Developments in Aryl Radical and Medicinal Chemistry

Synthesis of (S)-(+)-cericlamine through lipase-catalyzed aminolysis of azo acetates

Copper‐Catalyzed Trifluoromethylation of Hydrazones Leading to the Formation of Quaternary α‐Trifluoromethyl Diazenes

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