Cycloaddition reactions amino acids

Thiophene-3-carboxylic acid, 2-amino-azo dyes from, 1, 329 cycloaddition reactions, 4, 789 reactions, 4, 810... 

A series of chiral boron catalysts prepared from, e.g., N-sulfonyl a-amino acids has also been developed and used in a variety of cycloaddition reactions [18]. Corey et al. have applied the chiral (S)-tryptophan-derived oxazaborolidine-boron catalyst 11 and used it for the conversion of, e.g., benzaldehyde la to the cycloaddition product 3a by reaction with Danishefsky s diene 2a [18h]. This reaction la affords mainly the Mukaiyama aldol product 10, which, after isolation, was converted to 3a by treatment with TFA (Scheme 4.11). It was observed that no cycloaddition product was produced in the initial step, providing evidence for the two-step process. 

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. 

In an extension of this work Scheeren et al. studied a series of derivatives of N-to-syl-oxazaborolidinones as catalysts for the 1,3-dipolar cycloaddition reaction of 1 with 2b [29]. The addition of a co-solvent appeared to be of major importance. Catalyst 3b was synthesized from the corresponding amino acid and BH3-THF, hence, THF was present as a co-solvent. In this reaction (-)-4b was obtained with 62% ee. If the catalyst instead was synthesized from the amino acid and... 

The enantioselective inverse electron-demand 1,3-dipolar cycloaddition reactions of nitrones with alkenes described so far were catalyzed by metal complexes that favor a monodentate coordination of the nitrone, such as boron and aluminum complexes. However, the glyoxylate-derived nitrone 36 favors a bidentate coordination to the catalyst. This nitrone is a very interesting substrate, since the products that are obtained from the reaction with alkenes are masked a-amino acids. One of the characteristics of nitrones such as 36, having an ester moiety in the a position, is the swift E/Z equilibrium at room temperature (Scheme 6.28). In the crystalline form nitrone 36 exists as the pure Z isomer, however, in solution nitrone 36 have been shown to exists as a mixture of the E and Z isomers. This equilibrium could however be shifted to the Z isomer in the presence of a Lewis acid [74]. 

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. 

Silica gel [11] or alumina [11a, 12] alone, or silica and alumina together modified by Lewis-acid treatment [13] and zeolites [14], have been widely used as catalysts in Diels-Alder reactions, and these solids have also been tested as catalysts in asymmetric Diels-Alder reactions [12,13b,14]. Activated silica gel and alumina at 140 °C were used [15] to catalyze the asymmetric cycloaddition of (-)-menthyl-N-acetyl-a, S-dehydroalaninate (3) (R = NHCOMe) with cyclopentadiene in the key step for synthesizing optically active cycloaliphatic a-amino acids. When the reactions were carried out in the absence of solvent, a higher conversion was obtained. Some results are reported in Table 4.5 and compared with those obtained by using silica and alumina modified by treatment with Lewis acids. Silica gel gives a reasonable percentage of conversion after 24 h with complete diastereofacial selectivity in exo addition. 

The complex obtained from commercially available chiral a-amino acids (AA) with Cu + ion induces asymmetry in the Diels-Alder reaction of 31 (R = H) with 32. By using 10% Cu(II)-AA (AA = L-abrine) the cycloaddition occurs e/iJo-stereoselectively in 48 h at 0°C with high yield and with acceptable enantioselectivity ee = 1A%). This is the first example of enantioselective Lewis-acid catalysis of an organic reaction in water [9b]. 

If an aliphatic amino group is next to an electron-withdrawing group such as CO2R, CN, CHO, COR and has a hydrogen, reaction with aqueous nitrous acid gives a diazo compound (Eq. 11.4). Such compounds are used widely in 1,3-dipolar cycloaddition reactions, which will be covered in Chapter 12. 

Summary N-Silylation is a crucial prerequisite for the synthesis of interesting nonnatural amino acids via cycloaddition reactions of unsaturated amines. 

Pyranopyrrolothiazoles can be prepared in a similar way to certain pyrano- and thiopyrano-pyrrolizines and pyrrolizinopyridines as discussed earlier. Thus, thiazolidine-4-carboxylic acid reacts with the aldehyde 179 to give a 2 1 mixture of 180 and 181 (Equation 16). This reaction is a 1,3-dipolar cycloaddition of the alkene to the 1,3-dipole formed from reaction of the amino acid amine with the aldehyde <1988T4953, 1990T2213>. The alkyne analogue of 179 is similarly converted into 182 (Equation 17). 

Click chemistry has been particularly active in various fields this year. For example, ample applications of click chemistry have been seen in carbohydrate chemistry. Various /weiido-oligosacchardies and amino acid glycoconjugates were synthesized via an intermolecular 1,3-dipolar cycloaddition reaction using easily accessible carbohydrate and amino acid derived azides and alkynes as building blocks <06JOC364>. The iterative copper(I)-catalyzed... 

Amino acids labeled with DNS-C1 were determined using the Ru(bpy)32+ CL reaction after HPLC separation with a reversed-phase column [104, 105], DNS derivatives are expected to produce intense CL owing to their secondary and tertiary amino groups. The detection limit for DNS-Glu was 0.1 pM (2 pmol/ injection). Although underivatized amino acids could be detected by Ru(bpy)32+ CL, the DNS derivatives showed improved detection limits by three orders of magnitude [105], An approach to convert primary amines to tertiary amines was also reported [106], In this method, divinyl sulfone (DVS) was used for a cycloaddition reaction of primary amines (Fig. 19). The DVS derivatives after HPLC separation were sensitively detected (e.g., detection limits for propylamine and 3-aminopentane were 30 and 1 pmol, respectively). 

Studies of the intramolecular cyclization of P-amino acids have included the use of camphor-derived oxazoline A-oxide 66 and a [3+2] cycloaddition reaction as a step in the formation of the amino acid with the required stereochemistry <00OL1053, OOEJOC1595>. A diastereoselective synthesis of a ip-methylcarbapenem intermediate utilises a cyclization of a P-amino acid <99CC2365>. 

In agreement with Schemes 2.211b and 2.211c, intramolecular cycloadditions of nitrones to 5-allyl- (Scheme 2.225) or 5-homoallylproline (Scheme 2.226), are fully regio- and stereoselective. These reactions are the key steps in the synthesis of functionalized azaoxobicyclo[X.3.0] alkane amino acids, mimics of a homoSer-Pro dipeptide (721). 

The optically active isoxazolidines obtained in these cycloaddition reactions can be easily transformed into biologically active 3 -amino acids, into j3-lactams and into important chiral building blocks such as y-amino alcohols. The multitude of synthetic results in these reactions is of course expected by the wide variety... 

Kotha and Brahmachary353 prepared some constrained a-amino acids using a rhodium mediated [2 + 2 + 2] cycloaddition reaction. The indane type of a-amino acids were synthesized by reacting diynes with monoynes using Wilkinson s catalyst354. Thus, the reaction of diyne 615 with 616 afforded a-amino acid derivative 617 (equation 176). 

An extensive review of the hetero-Diels-Alder reactions of 1-oxabuta-1,3-dienes has been published. Ab initio calculations of the Diels-Alder reactions of prop-2-enethial with a number of dienophiles show that the transition states of all the reactions are similar and synchronous.Thio- and seleno-carbonyl compounds behave as superdienophiles in Diels-Alder reactions with cyclic and aryl-, methyl-, or methoxy-substituted open-chain buta-1,3-dienes.The intramolecular hetero-Diels-Alder reactions of 4-benzylidine-3-oxo[l,3]oxathiolan-5-ones (100) produce cycloadducts (101) and (102) in high yield and excellent endo/exo-selectivity (Scheme 39). A density functional theoretical study of the hetero-Diels-Alder reaction between butadiene and acrolein indicates that the endo s-cis is the most stable transition structure in both catalysed and uncatalysed reactions.The formation and use of amino acid-derived chiral acylnitroso hetero-Diels-Alder reactions in organic synthesis has been reviewed. The 4 + 2-cycloadditions of A-acylthioformamides as dienophiles have been reviewed. ... 

The [3+2] cycloaddition strategy provides an effective method to access valuable intermediates for the construction of biologically important alkaloids, amino acids, amino carbohydrates and P-lactams [58-62]. The reaction involves the concerted pericyclic addition of a dipole and a dipolarophile and considerable efforts have been made to render these reactions asymmetric nsing Lewis acid catalysis and chiral anxiliaries [63]. 

Keywords Absolute configuration. Amino acids, Bicyclopropylidene, Coupling reactions. Cycloadditions, Cyclopropanation, Cyclopropanes, Organolithium derivatives. Palladium catalysis. Radical reactions. Small ring polycycles, Spiro compounds. Strain energy. Sulfides... 

Keywords Absolute configuration, Amines, Amino acids, Carbenes, Cascade reactions, 2-chloro-2-cyclopropylideneacetates. Combinatorial libraries. Cycloadditions, Cyclobutenes, Cyclopropanes, Diels-Alder reactions. Heterocycles, Michael additions. Nitrones, Nucleophilic substitutions, Peptidomimetics, Palladium catalysis. Polycycles, Solid phase synthesis, Spiro compounds. Thiols... 

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