New Method for Generation of Alkenylidenecarbenes from Propargylic Methanesulfonates and Its Use in Regioselective C-H Insertion Reactions

Katsuhira, Takeshi; Harada, Toshiro; Oku, Akira

doi:10.1021/jo00093a039

Cited by 14 publications

(38 citation statements)

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“…19 Several methods exist to prepare α-hydroxyallenes: addition of lithiated allenes to aldehydes or ketones; 20,21 hydride reduction or Grignard addition onto propargylic oxiranes; 16,22 [2,3]-Wittig rearrangement of propargyl ethers; 23 insertion of alkenylidene carbenes into the α C-H bond of alkoxides. 24 We present a new and mild method that is compatible with various chemical functionalities to prepare α-hydroxy-allenes from selenylated 1,3-dienes after oxidation with hydrogen peroxide. First experiments were performed with stabilized 1,3-dienes 3c-8c derived from cinnamaldehyde.…”

Section: Allenes Formationmentioning

confidence: 99%

Selenylated dienes: synthesis, stereochemical studies by 77Se NMR, and transformation into functionalized allenes

et al. 2007

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2-Phenylselanyl-1,3-dienes 3-8 were prepared by a Wittig or Wittig-Horner-Emmons procedure starting from α-phenylselanylα,βunsaturated aldehydes. Ratio and configuration of each diene isomers were determined by 77 Se and 1 H NMR. These dienes were then oxidized into selenoxides, which could be isolated in some cases. In THF, [2,3]-sigmatropic rearrangement of allylic selenoxides, selenimides, and dihaloselenuranes occurred, yielding allenyl alcohols 12-15, allenyl carbamates 16c-19c, and 1-haloalkyl allenes 20c-22c, respectively.In particular, selenoxides play a pivotal role since the facile oxidation of alkyl phenylselenides allows the preparation of olefinic compounds and allylic alcohols under very mild conditions. 1,2 Our group was mainly involved in the studies of the reactivity of selenylated carbonyl derivatives allowing access to unsaturated, functionalized useful building-blocks 7 and their transformation into allenic alcohols via oxidation of 2-phenylselanyl-1,3-dienes. 8 These interesting selenylated dienes could also act as useful intermediates in organic synthesis, for example, as starting materials in Diels-Alder cycloaddition. 9,10 In the literature, very few preparations of 1-arylselanyl-1,3-butadienes are described: phenylselanyl alkylidene phosphoranes, phenylselanylalk-enals 11a or palladium-catalyzed cross coupling reactions. 11b A stereoselective synthesis of 1,3-dienyl selenides was re-ported by reaction of α-arylselanylvinylstannanes with vinyl halides 11c or by means of α-alkenylzirconium complexes with α-phenylselanylvinyl bromides. 11dHerein, we present a general access to 2-phenylselanyl-1,3-dienes along with an unambiguous determination of the stereochemistry by 77 Se NMR. Due to both vinylic and allylic position of the selanyl group in 2-phenylselanyl-1,3-dienes, sigmatropic rearrangements of selenoxides, selenimides, and dihalo-selenuranes were also studied, yielding, respectively, allenic alcohols, carbamates, and 1-haloalkyl allenes.

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Section: Allenes Formationmentioning

confidence: 99%

Selenylated dienes: synthesis, stereochemical studies by 77Se NMR, and transformation into functionalized allenes

et al. 2007

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“…Generation of vinylidenes from propargyl mesylates and their reaction with alcoholates [443]. Generation of vinylidenes from propargyl mesylates and their reaction with alcoholates [443].…”

Section: B-eliminationmentioning

confidence: 99%

The Alkylation of Carbanions

Dörwald

2004

Side Reactions in Organic Synthesis

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The deprotonation of organic compounds by strong, non-nucleophilic bases followed by C-alkylation with a suitable electrophile has become one of the most predictable and straightforward methods for formation of C-C bonds. The popularity of this chemistry is also a consequence of the often-seen close resemblance of feasible structural modifications by a deprotonation/alkylation strategy to an unsophisticated retrosynthetic analysis of a given target compound. Other reactions, which involve, for instance, substantial rearrangement of the carbon framework (e.g. Cope rearrangement, fragmentations, ring contractions or enlargements) are usually more difficult to take into account during retrosynthetic analysis.LDA and related, sterically hindered, lithium dialkylamides, first investigated by Levine [1], have completely replaced the more nucleophilic sodium amide, which had been the base of choice for many years [2]. Because the reactivity of an organometallic compound depends to a large extent on its state of aggregation (i.e. on the solvent and on additives) and on the metal, transmetalation of the lithiated intermediates and the choice of different solvents and additives emerged as powerful strategies for fine-tuning the reactivity of these valuable nucleophiles.In this chapter the alkylation of carbanions with simple carbon electrophiles will be discussed, with special emphasis on the structure-reactivity relationship of the carbanion and on side reactions. In this context the term "carbanion" refers to an intermediate prepared by in-situ deprotonation of an organic compound, followed by optional cation exchange (transmetalation), which tends to be alkylated at carbon by soft electrophiles such as MeI or PhCHO. This type of reactivity is characteristic of enolates with an ionic M-O bond or for organometallic compounds with a strongly polarized or ionic M-C bond, M typically being an alkali metal, Mg, Cu, or Zn. Carbanions can, alternatively, also be prepared by halogen-metal exchange [3-8], sulfoxide-or sulfone-metal exchange [9-13], or by transmetalation of stannanes. The most suitable reagents for performing such metalating exchange reactions are organometallic compounds with a metal-bound secondary or tertiary alkyl group, such as tBuLi, sBuLi, iPr 2 Zn [14, 15], or iPrMgHal [6]. These reagents are thermodynamically less stable than organometallic compounds with primary alkyl 5 146 Scheme 5.1. Approximate relative rates of proton transfer in water at thermoneutrality (DpK a = 0) [35, 39, 51]. 147 Scheme 5.2. The effect of fluorine on the acidity of organic compounds [24, 62-65]. 148 Scheme 5.3. Dependence of the reactivity of carbanions on their basicity [68, 72-74]. Regioselectivity of Deprotonations and AlkylationsThe organic chemist is occasionally confronted with the problem that a compound has several differrent X-H groups of similar pK a . If only one of these is to be alkylated, one option would be to perform a regioselective deprotonation. This can sometimes be achieved by exploiting small differences be...

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“…Propargyl alcohols 1a-b and propargyl silyl ether 8d were prepared by the reported procedure. [1][2][3] Alkynyl alcohols 1c-g and 15a-b are commercially available. The syntheses of propargyl ether 8a-c were shown below.…”

Section: Substrates and Reagentsmentioning

confidence: 99%

“…The integral values of the sp 2 -protons were used for the determination of the isomeric ratio. For a 93:7 mixture of (Z)-2a and 3a, 1 H NMR (CDCl 3 ) δ 0.86-0.98 (m, 9H), 1.12-1.83 (m, 26H), 2.18 (d, J = 3.1 Hz, 0.07H), 2.48 (br s, 0.93H), 4.42-4.49 (m, 1H), 5.69 (dd, J = 2.1, 0.8 Hz, 0.07H), 5.84 (dd, J = 1.8, 0.8 Hz, 0.07H), 6.27 (dd, J = 12.0, 2.3 Hz, 2 J SnH = 93.4 Hz, 0.93H), 6.59 (ddd, J = 12.0, 2.3, 1.0 Hz, 3 J SnH = 207.7 Hz, 0.93H).…”

Section: S5 / S17mentioning

confidence: 99%

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Regio‐ and Stereoselective Homolytic Hydrostannylation of Propargyl Alcohols and Ethers with Dibutylchlorostannane.

et al. 2004

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Organo-tin compoundsOrgano-tin compounds S 4800 Regio-and Stereoselective Homolytic Hydrostannylation of Propargyl Alcohols and Ethers withDibutylchlorostannane. -The Et 3 B-mediated reaction of γ-unsubstituted propargyl alcohols with Bu2SnClH results in formation of (Z)-vinylstannanes with high regio-and stereoselectivity. Regioselectivities concerning the reactions of corresponding alkyl propargyl ethers are lower than those of propargyl alcohols. -(MIURA*, K.; WANG, D.; MATSUMOTO, Y.; FUJISAWA, N.; HOSOMI*, A.; J. Org. Chem. 68 (2003) 22, 8730-8732; Dep. Chem., Univ. Tsukuba, Tsukuba, Ibaraki 305, Japan; Eng.) -S. Adam 12-174 2003 Organo-tin compounds

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New Method for Generation of Alkenylidenecarbenes from Propargylic Methanesulfonates and Its Use in Regioselective C-H Insertion Reactions

Cited by 14 publications

References 0 publications

Selenylated dienes: synthesis, stereochemical studies by 77Se NMR, and transformation into functionalized allenes

Selenylated dienes: synthesis, stereochemical studies by 77Se NMR, and transformation into functionalized allenes

The Alkylation of Carbanions

Regio‐ and Stereoselective Homolytic Hydrostannylation of Propargyl Alcohols and Ethers with Dibutylchlorostannane.

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