New Methylene Homologation Method for Cyclic Ketones

Liu, Huaqing; Sun, Chunrui; Lee, Nam Kyu; Henry, Roger F.; Lee, Daesung

doi:10.1002/chem.201201346

Cited by 47 publications

(39 citation statements)

References 49 publications

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“…Nucleophilic addition of TMS diazomethane to the carbonyl in 60 , followed by protonation with methanol led to the ring enlargement. Notably, this transformation proceeded in very satisfying yield even without prior protection of the hydroxy group in 60 . Desired ketone 45 was finally obtained with excellent regioselectivity after hydrolysis of the intermediate silyl enol ether.…”

Section: Structure‐pattern‐based Synthesis Of Sarpagine and Stemona Amentioning

confidence: 96%

“…Due to our optimized reaction conditions, gram quantities of compound 45 were synthesized, which represents the immediate precursor to the Fischer indole synthesis. Starting from ketone 45 , six natural and ten non‐natural congeners of the Sarpagine alkaloid family were accessed in a single chemical operation (Scheme –Scheme ) …”

Section: Structure‐pattern‐based Synthesis Of Sarpagine and Stemona Amentioning

confidence: 99%

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Structure‐Pattern‐Based Total Synthesis

Gerlinger

Gaich

2019

Chemistry A European J

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In this article the concept of structure‐pattern‐recognition and its application to total synthesis is summarized. By applying this synthetic strategy to the two biogenetically unrelated natural product families Sarpagine and Stemona alkaloids, a drastic increase of synthetic efficiency could be achieved. To highlight its potential, this strategy is compared with some elegant target‐oriented syntheses. The importance of strategic planning and synthesis design is clearly demonstrated.

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Section: Structure‐pattern‐based Synthesis Of Sarpagine and Stemona Amentioning

confidence: 96%

Section: Structure‐pattern‐based Synthesis Of Sarpagine and Stemona Amentioning

confidence: 99%

Structure‐Pattern‐Based Total Synthesis

Gerlinger

Gaich

2019

Chemistry A European J

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“…A new simple methylene homologation for estrone was described by Liu et al, who used lithium trimethylsilyl diazomethane, followed by treatment with silica gel [7]. We recently developed an efficient route for the synthesis of D-homoestrone and its derivatives from a readily available δ-alkenyl-D-secoestrone-3-benzyl ether [1,8].…”

Section: Introductionmentioning

confidence: 99%

Synthesis of antiproliferative 13α-d-homoestrones via Lewis acid-promoted one-pot Prins–Ritter reactions of d-secosteroidal δ-alkenyl-aldehydes

et al. 2015

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“…[2,23] An improved procedure was reported via bullvalone tosylhydrazone,providing bullvalene (3a)i na pproximately 5% yield from 2a in four steps. [10,24] In our new approach, bullvalene (3a)a nd phenylbullvalene (3b)were prepared from barbaralones 1a-b by athreestep procedure.Ahomologation reaction of 1a and 1b with the lithium anion of (trimethylsilyl)diazomethane [25] gave bullvalones 2a and 2b in 37 and 22 %y ield, respectively (Scheme 4). Formation of the corresponding enol triflates using LDAa nd Comins reagent, or LiHMDS and PhNTf 2 followed by immediate reduction with nBu 3 SnH and Pd(PPh 3 ) 4 as catalyst, [26] afforded 3a and 3b [27] in 44 %a nd 60 %y ield, respectively,whose structures were confirmed by X-ray diffraction.…”

Section: Entry 16)mentioning

confidence: 99%

Synthesis of Barbaralones and Bullvalenes Made Easy by Gold Catalysis

Ferrer

Echavarren

2016

Angewandte Chemie

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The gold(I)-catalyzed oxidative cyclization of 7-ethynyl-1,3,5-cycloheptatrienes gives 1-substituted barbaralones in ageneral manner,which simplifies the access to other fluxional molecules.A sa ne xample,w er eport the shortest syntheses of bullvalene,p henylbullvalene,a nd disubstituted bullvalenes,a nd ar eadily accessible route to complex cagetype structures by further gold(I)-catalyzed reactions.Fluxional molecules,s uch as barbaralone (1a), bullvalone (2a), and bullvalene (3a)h ave been central to the understanding of the phenomena of valence tautomerism (see Figure 1). [1,2] These molecules undergo low energy [3.3]-sigmatropic rearrangements,w hich in the case of bullvalene lead to 1209 600 degenerate tautomers, [3][4][5] whereas al ower number of constitutional isomers are possible for substituted bullvalenes [6][7][8] and only two exist for barbaralone (1a).[9]Syntheses of these fluxional molecules requires multistep procedures that proceed with low overall yield, often using explosive and toxic diazomethane.T hus,t he optimized synthesis of barbaralone (1a), en route to bullvalene (3a), [10] starts with the Büchner reaction of ethyl diazoacetate with benzene to form 4, [11,12] which is converted into 1a in four steps via diazomethyl ketone 5 (Scheme 1).[10] Bullvalene (3a)can be prepared from 1a in four additional steps by two different procedures by homologation of 1a to bullvalone (2a)w ith diazomethane. [2,10] Barbaralone (1a)h as also been prepared from (cyclooctatetraene)tricarbonyliron in two steps in approximately 36 %yield. [13] 1-Methylbarbaralone (1w)w as prepared by ap rocedure similar to that shown in Scheme 1using ethyldiazomethane in the reaction with cycloheptatriene carbamoyl chloride to form the homologue of 5.[9b] Although some ingenious syntheses of highly substituted bullvalenes have been designed, [8] most bullvalenes have been prepared from parent 3a.T hus,f or example,p henylbullvalene (3b)w as obtained in three steps (26 %y ield) from 3a by dibromination, dehydrobromination with KOtBu, and reaction of the resulting bromobullvalene with Ph 2 CuLi.[7d]Current synthetic art does not allow preparation of substituted barbaralones in ag eneral way, [14] which limits the access to fluxional homologues and other theoretically interesting molecules. [12,15] We have recently found that 7-aryl-1,3,5-cycloheptatrienes undergo ag old(I)-catalyzed retro-Büchner reaction to form highly reactive aryl gold(I) carbenes (a decarbenation reaction).[16] However,7 -ethynyl-1,3,5-cycloheptatrienes (6)react differently to form fluxional barbaralyl gold(I) intermediates 7;a fter as eries of complex rearrangements 7 finally leads to indenes 8 and/or 9,depending on the gold catalyst (Scheme 2).[17] Since the goldcatalyzed oxidation of alkynes has been shown to take place readily with oxidants such as sulfoxides,oramine-N-oxides to form a-oxo gold(I) carbenes, [18,19] we envisioned that the oxidation of intermediates 7 could lead to 1-substituted barbaralones 1 (Scheme 2). However,i ft he oxidati...

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New Methylene Homologation Method for Cyclic Ketones

Cited by 47 publications

References 49 publications

Structure‐Pattern‐Based Total Synthesis

Structure‐Pattern‐Based Total Synthesis

Synthesis of antiproliferative 13α-d-homoestrones via Lewis acid-promoted one-pot Prins–Ritter reactions of d-secosteroidal δ-alkenyl-aldehydes

Synthesis of Barbaralones and Bullvalenes Made Easy by Gold Catalysis

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