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Ketenes amino

Following the isolation of (—)-S-N-nor-methylskytanthine (32) (36), Pombo-Villar and co-workers described a synthesis of the alkaloid in chiral form (Scheme 11) (193). A ketene amino-Claisen rearrangement (194) was... [Pg.319]

Although the thio-Claisen transposition affords various possibilities of synthesis with stereocontrol, few examples of natural product synthesis have been described. Takano s group was a pioneer in this field with the synthesis of nine-membered indole alkaloids (Scheme9.32) related to deavamine [152] and velbana-mine [153]. The key step involved the transformation of a sulfonium salt into a corresponding ketene amino thioacetal, which underwent the thio-Claisen transposition. A similar strategy was used for the synthesis of the strychnos alkaloid framework [154]. [Pg.451]

The (5)-phenylethylamine-derived norbomene 14 also serves as the starting point for the synthesis of the natural alkaloid, (-)-y-iV-normethylsky-tanthine (79) [26]. The key transformation of the 2-azabicyclo[2.2.1]heptane skeleton into the 3-azabicyclo[4.3.0]nonane backbone, embodied in the natural alkaloid, involves the ketene amino Claisen rearrangement as reported by Roberts et al. [27] (see Scheme 2.3 and the prior equation in section 2.3.1). Treatment of 14 with dichloroketene, generated in situ from dichloroacetyl chloride and Hunig s base, at 2°C for 16h, gives lactam 80 in... [Pg.63]

Acylation. Reaction conditions employed to acylate an aminophenol (using acetic anhydride in alkaU or pyridine, acetyl chloride and pyridine in toluene, or ketene in ethanol) usually lead to involvement of the amino function. If an excess of reagent is used, however, especially with 2-aminophenol, 0,A/-diacylated products are formed. Aminophenol carboxylates (0-acylated aminophenols) normally are prepared by the reduction of the corresponding nitrophenyl carboxylates, which is of particular importance with the 4-aminophenol derivatives. A migration of the acyl group from the O to the N position is known to occur for some 2- and 4-aminophenol acylated products. Whereas ethyl 4-aminophenyl carbonate is relatively stable in dilute acid, the 2-derivative has been shown to rearrange slowly to give ethyl 2-hydroxyphenyl carbamate [35580-89-3] (26). [Pg.310]

Halogenopyrimidines react with active methylene groups, such as those in diethyl malonate, ethyl cyanoacetate, ketene diethylacetal, etc. For example, 4-chloro-6-methyl-5-nitropyrimidin-2-amine (454) and dimethyl sodiomalonate give dimethyl 2-amino-6-methyl-5-nitropyrimidin-4-ylmalonate (455) (63ZOB3132) 2-chloro-4,6-... [Pg.103]

Reaction of 2-alkyl- -pyrrolines and 2-alkyl- -piperideines with acid chlorides leads to ring-opening and formation of N-acylated amino ketones (131, = 1, 2) (211-213). Ketene reacts with J -piperideine to form a tricyclic derivative (132) (214). [Pg.282]

The facile formation of cyclobutane products is indeed another important contribution of enamine chemistry (302-306). The formation of cyclobutanes has also been found in the closely related reactions of amino acetal derivatives of ketenes with acrylic esters (307). [Pg.361]

Analogously, the reactions of ketene aminals with ketene or dimethyl ketene gave y-amino-a-pyrones and the linear acylation products, respectively 422). [Pg.395]

Asymmetric synthesis of 3-amino (3-lactams via Staudinger ketene-imine cycloaddition reaction 98KGS1448. [Pg.228]

Scheeren et al. reported the first enantioselective metal-catalyzed 1,3-dipolar cycloaddition reaction of nitrones with alkenes in 1994 [26]. Their approach involved C,N-diphenylnitrone la and ketene acetals 2, in the presence of the amino acid-derived oxazaborolidinones 3 as the catalyst (Scheme 6.8). This type of boron catalyst has been used successfully for asymmetric Diels-Alder reactions [27, 28]. In this reaction the nitrone is activated, according to the inverse electron-demand, for a 1,3-dipolar cycloaddition with the electron-rich alkene. The reaction is thus controlled by the LUMO inone-HOMOaikene interaction. They found that coordination of the nitrone to the boron Lewis acid strongly accelerated the 1,3-dipolar cycloaddition reaction with ketene acetals. The reactions of la with 2a,b, catalyzed by 20 mol% of oxazaborolidinones such as 3a,b were carried out at -78 °C. In some reactions fair enantioselectivities were induced by the catalysts, thus, 4a was obtained with an optical purity of 74% ee, however, in a low yield. The reaction involving 2b gave the C-3, C-4-cis isomer 4b as the only diastereomer of the product with 62% ee. [Pg.218]

Compounds of special interest whose preparation is described include 1,2,3-benzothiadiazole 1,1-dioxide (a benzyne precursor under exceptionally mild conditions), bis(l,3-diphenylimida-zolidinylidene-2) (whose chemistry is quite remarkable), 6- di-melhylamino)julvene (a useful intermediate for fused-ring non-benzenoid aromatic compounds), dipkenylcyclopropenone (the synthesis of which is a milestone in theoretical organic chemistry), ketene di(2-melhoxyethyl) acetal (the easiest ketene acetal to prepare), 2-methylcyclopenlane-l,3-dione (a useful intermediate in steroid synthesis), and 2-phenyl-5-oxazolone (an important intermediate in amino acid chemistry). [Pg.145]

Equiv of the imine 2 is dissolved in the appropriate solvent and 1 cquiv of the silyl ketene acetal 1 is added, the mixture is cooled to —70 °C and 0.1 equiv of TMSTf is added. After 15 h the reaction is quenched with H.O. 10% aq NH40H is added to make the piT basic, and the reaction mixture is extracted with F.tOAc. The crude product (obtained after the usual workup) is subjected to silica gel chromatography (pet. cthcr/Et20) to give the pure /J-amino ester 3. [Pg.762]

The photolysis of o-quinone diazides was carefully investigated by Stis in 1944, many years before the development of photoresists. Scheme 10-102 shows the photolysis sequence for the diazoquinone 10.75 formed in the diazotization of 2-amino-1-naphthol. The product of the photolytic step is a ketocarbene (10.76), which undergoes a Wolff rearrangement to a ketene (10.77). In the presence of water in-dene-3-carboxylic acid (10.78) is formed this compound is highly soluble in water and can be removed in the development step. The mechanism given in Scheme 10-102 was not postulated as such by Stis, because in 1944 ketocarbenes were unknown (for a mechanistic discussion of such Wolff rearrangements see review by Zollinger, 1995, Sec. 8.6, and Andraos et al., 1994). [Pg.284]

The superior donor properties of amino groups over alkoxy substituents causes a higher electron density at the metal centre resulting in an increased M-CO bond strength in aminocarbene complexes. Therefore, the primary decarbo-nylation step requires harsher conditions moreover, the CO insertion generating the ketene intermediate cannot compete successfully with a direct electro-cyclisation of the alkyne insertion product, as shown in Scheme 9 for the formation of indenes. Due to that experience amino(aryl)carbene complexes are prone to undergo cyclopentannulation. If, however, the donor capacity of the aminocarbene ligand is reduced by N-acylation, benzannulation becomes feasible [22]. [Pg.131]

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. [Pg.157]

Photodriven reactions of Fischer carbenes with alcohols produces esters, the expected product from nucleophilic addition to ketenes. Hydroxycarbene complexes, generated in situ by protonation of the corresponding ate complex, produced a-hydroxyesters in modest yield (Table 15) [103]. Ketals,presumably formed by thermal decomposition of the carbenes, were major by-products. The discovery that amides were readily converted to aminocarbene complexes [104] resulted in an efficient approach to a-amino acids by photodriven reaction of these aminocarbenes with alcohols (Table 16) [105,106]. a-Alkylation of the (methyl)(dibenzylamino)carbene complex followed by photolysis produced a range of racemic alanine derivatives (Eq. 26). With chiral oxazolidine carbene complexes optically active amino acid derivatives were available (Eq. 27). Since both enantiomers of the optically active chromium aminocarbene are equally available, both the natural S and unnatural R amino acid derivatives are equally... [Pg.182]

The mild reaction conditions and the obviously high potential driving force of the ketene Claisen rearrangement recommended the use of the process for more complex systems. The first series of this type of reaction suffered from severe limitations. On the one hand, only electron-deficient ketenes added to the allylamines, and useful yields of the lactams had exclusively been achieved by employing dichloroketene [57, 58 a]. On the other hand, the rearrangement was restricted to either monosubstituted olefins in the amino fragment or the... [Pg.176]

Scheme 27 Addition of nitronates, enolates and silyl ketene acetals to chiral a-amino imines and iminium ions... Scheme 27 Addition of nitronates, enolates and silyl ketene acetals to chiral a-amino imines and iminium ions...
Hepatite Virus NS3/4A having the pyrrolidine-5,5-trans-lactam skeleton [83], starting from (R)- and (S)-methionine, respectively. The key step is the addition of the proper silyl ketene acetal to an iminium ion, e.g., that generated by treatment of the intermediate 177 with boron trifluoride, which provided the adduct 178 with better diastereoselectivity than other Lewis acids. Inhibitors of hepatitis C virus NS3/4A were efficiently prepared by a similar route from (S)-methionine [83]. The addition of indole to a chiral (z-amino iminium ion was a completely diastereoselective step in a reported synthesis of tilivalline, a natural molecule which displays strong cytotoxicity towards mouse leukemia L 1210 [84]. [Pg.33]

With trimethylsilyl iodide 17 the 0,N-acetal 457 gives the iminium iodide as reactive intermediate this converts the enol silyl ether 107 a in situ into the Man-nich-base 669, in 81% yield, and hexamethyldisiloxane 7 [195]. On treatment of the 0,N-acetal 473 (or the N-silylated Schiff base 489) with TMSOTf 20 (or Zny, the intermediate iminium triflate adds to the ketene acetal 663 to give mefhoxytri-methylsilane 13 a and silylated / -amino esters such as 670, which are readily transsilylated by methanol to give the free / -aminoester [70, 196] (Scheme 5.61). [Pg.117]

Fe(OTf)2-catalyzed aziridination of enol silyl ethers with PhlNTs followed by ring opening led to a-N-tosylamido ketones in good yields (Scheme 27) [81]. With silyl ketene ketal (R = OMe) as substrate, the N-tosyl-protected amino acid ester was obtained in 50% yield. In contrast, the copper (I) salt CuClOq was found not effective for this substrate [82]. [Pg.132]

Reaction of 3-amino-4-imino-4//-pyrido[l,2- ]pyrazine 306 (R = 4-MeC6H4) with ketenes 328, prepared in situ from the appropriate acetyl chloride with NEt3, yielded tricyclic derivatives 329 (Scheme 29) <1999JPR332>. Pyridine-3,4-dicarboxylates 330 were obtained from 4//-pyrido[l,2- pyrazines 307 with DMAD in refluxing toluene. [Pg.140]

Ketene dithioacetal 130 reacts with 3-amino-2-pyrazolin-5-one 129 to give the highly functionalized pyrazolopyridine 131, which is converted into the bispyrazolopyridine 132 by reaction with hydrazine hydrate (Scheme 9) <1997JCM256>. [Pg.728]

It was first observed that reactions of imines with ketene silyl acetals proceeded smoothly in the presence of 5mol.% Yb(OTf)3 to afford the corresponding /3-amino ester derivatives in moderate yields.50 However, Sc(OTf)3 was found to be a more active catalyst in this reaction. Benzoylhy-drazones also react with ketene silyl acetals in the presence of a catalytic amount of Sc(OTf)3 to afford the corresponding adducts in high yields (Scheme 11).51 In contrast, catalytic activation of benzoylhydrazones by use of a typical Lewis acid such as TiCl4, SnCl4, or BF3-OEt2, etc. is not effective. [Pg.403]

Other non-traditional preparations of 1,2,3-triazoles have been reported. The rearrangement in dioxane/water of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole into (2-aryl-5-phenyl-27/-l,2,3-triazol-4-yl)ureas was investigated mechanistically in terms of substituents on different pathways <06JOC5616>. A general and efficient method for the preparation of 2,4-diary 1-1,2,3-triazoles 140 from a-hydroxyacetophenones 139 and arylhydrazines is reported <06SC2461>. 5-Alkylamino-] //-], 2,3-triazoles were obtained by base-mediated cleavage of cycloadducts of azides to cyclic ketene acetals <06S1943>. Oxidation of N-... [Pg.229]


See other pages where Ketenes amino is mentioned: [Pg.264]    [Pg.265]    [Pg.137]    [Pg.1231]    [Pg.186]    [Pg.76]    [Pg.216]    [Pg.1250]    [Pg.71]    [Pg.154]    [Pg.207]    [Pg.136]    [Pg.171]    [Pg.172]    [Pg.185]    [Pg.1231]    [Pg.298]    [Pg.349]    [Pg.350]    [Pg.199]    [Pg.204]    [Pg.239]    [Pg.170]    [Pg.95]    [Pg.136]   
See also in sourсe #XX -- [ Pg.72 ]




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3-Amino esters from chiral silyl ketene acetals

Amino acid-derived catalysts ketenes

Ketene aminals 3-amino

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