Chiral Triarylcarbenium Ions in Asymmetric Mukaiyama Aldol Additions

Chen, Chien‐Tien; Chao, Shi‐Deh; Yen, Kuao-Chung; Chen, Chung-Horng; Chou, and Iy-Chen; Hon, Sang-Weng

doi:10.1021/ja970900o

Cited by 81 publications

(38 citation statements)

References 19 publications

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“…In contrast to the planar fluorenyl [52] and reasonably planar and conformationally more mobile 9H-xanthenyl, 9H-thioxanthenyl, 9H-thioxanthenyl-10,10-dioxide, N-benzyl-9,10-dihydroacridinyl, and 9,10-dihydroanthracenyl tricyclic moieties, where the formed cyclohexa-2,5-dienone ring is expected to be subjected to more severe steric interactions as a result of peri-1,8-hydrogen interactions of the annulated A and B benzene rings, the seven-membered ring systems may assume conformations in which the dienone ring may readily be accommodated. [53][54][55] In contrast, in the open ring system of diphenyl(p-methoxyphenyl)methanols (tritanols), the aryl rings are twisted out of plane and the assumed conformations of the formed p-QM may also readily accommodate the formed cyclohexa-2,5-dienone moiety, but may also relatively easily revert back to the phenolic structure, whereas in the seven-membered B-ring systems, the conformational barriers are suggested to be much higher and hence would account for the higher stability and reluctance of these systems to revert to the phenolic forms in basic medium. The alcohol 7a dealkylated smoothly to give the p-QM, 8a in excellent yield.…”

Section: Resultsmentioning

confidence: 99%

The Synthesis of Novel p‐Quinone Methides: O‐Dealkylation of5‐(p‐Alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ols and Related Compounds

Taljaard¹,

Taljaard²,

Imrie³

et al. 2005

Eur J Org Chem

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The synthesis of a series of novel tricyclic p‐quinone methides (p‐QMs) from 5‐(p‐alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ol and related substrates in moderate‐to‐good yields is reported. The reaction is proposed to proceed under mild acidic conditions by O‐dealkylation of the p‐alkoxy group on the p‐position of the pendant 5‐aryl ring on the B‐ring of the tricyclic system.The effect of different alkyl groups on the oxygen atom, as well as substituent groups on the phenyl ring flanking the O‐alkyl group has also been investigated The mechanism of the reaction is discussed in terms of the relatively high intermediate cation stabilities, the possible intermediacy of a hemiketal, as well as conformational effects. Various modifications to the central seven‐membered B‐ring to introduce more rigidity to the tricyclic system have been made and the scope of the reaction further elaborated. Furthermore, the single crystal structure of dienone 14 has been determined and the p‐quinone methide shown to be non‐planar, which would account for the relative conformational rigidity of these systems and their ability to accommodate the planar cyclohexa‐2,5‐dienone moiety and thus explain the stability of these systems relative to their 5‐ and six‐membered B‐ring counterparts. These compounds may be useful for the synthesis of novel dyes or compounds which may exhibit photochromic and thermochromic properties. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Section: Resultsmentioning

confidence: 99%

The Synthesis of Novel p‐Quinone Methides: O‐Dealkylation of5‐(p‐Alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ols and Related Compounds

Taljaard¹,

Taljaard²,

Imrie³

et al. 2005

Eur J Org Chem

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“…[14] When spiro-fluorene is incorporated at the C5-position of the dibenzosuberene template, the new molecular connects the individual o-position of two phenyl rings in an HT-type 9,9-diphenylfluorene framework to the C2-C3 edge of a functionalized ET-type quinoxaline (6)(7)(8)(9). [15,16] Therefore, the resultant 1:1 hybrid is potentially ambipolar and can act as a central fluorescent unit with tunable emission colors by judicious choices of the C5-and C8-appendages ( Figure 3). The optoelectronic performance is two times better when 7 is utilized as an ET and emitting layer.…”

Section: Organic Ambipolar Conjugated Molecules For Fluorescent Emittersmentioning

confidence: 99%

Organic Ambipolar Conjugated Molecules for Electronics: Synthesis and Structure–Property Relationships

Jiang

2010

Macromol. Rapid Commun.

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The field of organic electronics has been developed vastly in the past two decades, and the performance and lifetime of these devices are critically dependent on the materials development, device design, deposition processes, and modeling, among which the active materials of organic semiconductor play a crucial role. The unique properties of organic semiconductor are largely based on the versatility to synthesize multifunctional organic conjugated materials by judicious molecular design. To effectively adjust the optoelectronic properties, especially energy levels, of organic semiconductor, the scientists have presented a synthesis methodology of organic ambipolar conjugated molecules, in which typical p-dope type and n-dope type segments are incorporated into one molecule. The present review summarizes the progress on organic ambipolar conjugated molecules for electronics in the past few years. Some issues to be addressed are also highlighted and discussed.

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“…[10][11][12] Our interest in this particular transformation was further stimulated by speculating that the lack of established catalytic asymmetric HDA reactions might stem from a competing silylium-catalyzed background reaction. [13] We had previously shown that disulfonimide-based catalysis offers an efficient solution to this problem in Mukaiyama aldolizations.…”

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confidence: 99%

Highly Enantioselective Hetero‐Diels–Alder Reaction of 1,3‐Bis(silyloxy)‐1,3‐dienes with Aldehydes Catalyzed by Chiral Disulfonimide

2012

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Originating from observation by Danishefsky et al. that hetero-Diels-Alder (HDA) reactions of 1-methoxy-3-(trimethylsilyloxy)butadiene (Danishefskys diene) with aldehydes are accelerated by Lewis acids [Eq. (1); TMS = trimethylsilyl], [1] asymmetric variants became extensively studied and utilized in the synthesis of enantioenriched six-membered oxygen-containing heterocycles.[2] Indeed, several efficient metal-based chiral Lewis acids have been developed for this reaction.[3] Recently, Rawal and co-workers introduced a metal-free, hydrogen-bonding catalyst for asymmetric HDA reactions of 1-dimethylamino-3-tert-butyldimethylsilyloxy-1,3-butadiene (Rawals diene) with aldehydes [Eq. (1), TBS = tert-butyldimethylsilyl].[4] Despite all this progress however, the present catalytic systems for asymmetric HDA reactions are largely limited to the originally introduced dienes, and substituted and functionalized dienes have proven to be highly challenging substrates.[3c,e,g, 5] As a consequence, only few catalytic asymmetric syntheses of 2,6-disubstituted dihydropyrones have been reported and the catalytic enantioselective synthesis of 2,5,6-trisubstituted dihydropyrones is entirely unknown. [6,7] Herein, we report a highly enantioselective HDA reaction of aldehydes with substituted 1,3-bis(silyloxy)-1,3-dienes catalyzed by a novel, highly fluorinated, chiral disulfonimide [Eq. (2)].Recently our group has introduced chiral disulfonimides (DSI) as effective catalysts of asymmetric Mukaiyama and vinylogous Mukaiyama aldol reactions with aldehydes. [8,9] We hypothesized that such a catalyst could also promote the mechanistically related HDA reactions of 1,3-bis(silyloxy)-1,3-dienes, which surprisingly have previously been utilized only in non-asymmetric catalysis. [10][11][12] Our interest in this particular transformation was further stimulated by speculating that the lack of established catalytic asymmetric HDA reactions might stem from a competing silylium-catalyzed background reaction.[13] We had previously shown that disulfonimide-based catalysis offers an efficient solution to this problem in Mukaiyama aldolizations.To explore the principal utility of our DSI catalysts in HDA reactions, we initially studied our previously used chiral disulfonimide catalyst 1 in the reaction of 2-naphthaldehyde with the commercially available diene 3. These experiments showed that the product 4 could indeed be obtained in the presence of 5 mol % of catalyst 1 at À78 8C in Et 2 O in good yield and reasonable enantioselectivity (Table 1, entry 1). We reasoned that improving the steric and electronic properties of the catalyst by incorporating large perfluorinated substitu- e.r.

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Chiral Triarylcarbenium Ions in Asymmetric Mukaiyama Aldol Additions

Cited by 81 publications

References 19 publications

The Synthesis of Novel p‐Quinone Methides: O‐Dealkylation of5‐(p‐Alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ols and Related Compounds

The Synthesis of Novel p‐Quinone Methides: O‐Dealkylation of5‐(p‐Alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ols and Related Compounds

Organic Ambipolar Conjugated Molecules for Electronics: Synthesis and Structure–Property Relationships

Highly Enantioselective Hetero‐Diels–Alder Reaction of 1,3‐Bis(silyloxy)‐1,3‐dienes with Aldehydes Catalyzed by Chiral Disulfonimide

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