Acetonitrile aldol reaction

Owing to the high Lewis acidity the group 14 organometallic cations are polymerization catalysts par excellence. so Silanorbonyl cations and triethylsilyl arenium have been shown to be efficient catalysts for metal-free hydrosilylation reactions. Chiral silyl cation complexes with acetonitrile have been applied as cata -lysts in Diels Alder-type cyclization reactions °792 intramolecularly stabilized tetracoordinated silyl cations have been successfully used as efficient catalysts in Mukaiyama-type aldol reactions. 

An iron-catalyzed multicomponent reaction of aldehyde 4a, acetophenone, acetyl chloride and acetonitrile, which was used as the solvent, gave P-amino ketones such as 32 (Scheme 8.11) [41]. It was assumed that the sequence starts with an aldol reaction of aldehyde and ketone and then proceeds further with a displacement of a P-acetoxy group by the nucleophilic nitrile-nitrogen. 

C-(2-aminoethyl)-4,6-0-benzylidene-2-deoxy-a-D-n 6o-468 and D-arabino-hexopyranoside469 by hydrogenation of cyanomethylene or cyanomethyl groups introduced into methyl 4,6-0-benzylidene-2-deoxy-a-D-ertt/zro-hexopyranosid-3-ulose via a Wittig reaction, or a modified aldol reaction with acetonitrile, respectively. 

Ghosh et al. reported that the chiral oxazolidinone 87, derived from (1S,2R)-cis-l-amino-2-indanol (86), underwent a highly diastereoselective. vyn-aldol reaction with a variety of aldehydes30 (Scheme 2.1cc). Reaction of the indanolamine 86 with disuccinyl carbonate in acetonitrile gave the oxazolidinone 87, which was deprotonated with -BuLi and reacted with propionyl chloride to provide the N-propionyl derivative 88. Reaction of 88 with n-BioBOTf and... 

A recent general study on the reactivity of 3-mono-O-activated dienes 2-6 having an alkyl group at C-l and 2-7 in the presence of a Lewis acid was performed by Palenzuela et al. [72]. The best yields of the cycloadducts 2-8 were obtained with BF3-OEt2 in diethyl ether with an endo/exo-selectivity of 6 1 (Fig. 2-2). Good results were also found with LiBF4 in acetonitrile/benzene. Aldol reactions [73], silatropic ene reactions [74] and loss of the silyl group [75] were not observed under these conditions. 

For benzoic acid acceleration in Yb(OTf)3-catalyzed allylation of aldehydes in acetonitrile, (a) As-pinall, H.C. Greeves, N. Mclver, E. G. Tetrahedron Lett. 1998, 39, 9283. For acetic acid acceleration in Yb(fod)3-catalyzed ene reaction of aldehydes with alkyl vinyl ethers, ene reaction of aldehydes with alkyl vinyl ethers, (b) Deaton, M. V. Ciufolini, M.A. Tetrahedron Lett. 1993, 34, 2409. Yamamoto et al. reported Brpnsted acid-assisted chiral Lewis acids and Lewis acid-assisted Brpnsted acids which were used for catalytic asymmetric Diels-Alder reactions and protonations and stoichiometric asymmetric aza Diels-Alder reactions, aldol-type reactions of imines, and an aldol reaction, (c) Ishihara, K. Yamamoto, H. J. Am. Chem. Soc. 1994, 116, 1561. (d) Ishihara, K. Kurihara, H. Yamamoto, H. J. Am. Chem. Soc. 1996, 118, 3049. (e) Ishihara, K. Nakamura, S. Kaneeda, M. Yamamoto, H. J. Am. Chem. Soc. 1996, 118, 12854. (f) Ishihara, K. Miyata, M. Hattori, K. Tada, T. Yamamoto, H. J. Am. Chem. Sc c. 1994, 116, 10520. (g) Yamamoto, H. J. Am. Chem. Soc 1994, 116, 10520. (h) ishihara, K. Kurihara, H. Matsumoto, M. Yamamoto Ishihara, K. Kurihara, H. Matsumoto, M. Yamamoto, H. J. Am. Chem. Soc 1998, 120, 6920. 

The reaction of ethanol with ammonia on zeolite catalysts leads to ethylamine. If, however, the reaction is carried out in the presence of oxygen, then pyridine is formed [53]. MFI type catalysts H-ZSM-5 and B-MFI are particularly suitable for this purpose. Thus, a mixture of ethanol, NH3, H2O and O2 (molar ratio 3 1 6 9) reacts on B-MFI at 330 °C and WHSV 0.17 h 1 to yield pyridine with 48 % selectivity at 24 % conversion. At 360 °C the conversion is 81% but there is increased ethylene formation at the expense of pyridine. Further by-products include diethyl ether, acetaldehyde, ethylamine, picolines, acetonitrile and CO2. When applying H-mordenite, HY or silica-alumina under similar conditions pyridine yields are very low and ethylene is the main product. The one-dimensional zeolite H-Nu-10 (TON) turned out to be another pyridine-forming catalyst 54]. A mechanism starting with partial oxidation of ethanol to acetaldehyde followed by aldolization, reaction with ammonia, cyclization and aromatization can be envisaged. An intriguing question is why pyridine is the main product and not methylpyridines (picolines). It has been suggested in this connection that zeolite radical sites induced Ci-species formation. 

Lanthanide triflates were found to be excellent Lewis acid catalysts not only in aqueous media but also in organic solvents. The reaction of ketene silyl acetal 3 with benzaldehyde proceeded smoothly in the presence of 10mol% Yb(OTf)3 in dichloromethane at -78°C, to afford the corresponding aldol-type adduct in 94% yield. The same reaction at room temperature also went quite cleanly without side reactions and the desired adduct was obtained in 95% yield. No adduct was obtained in THF-water or toluene-ethanol-water, because hydrolysis of the ketene silyl acetal preceded the desired aldol reaction in such solvents. In other organic solvents such as toluene, THF, acetonitrile, and DMF, Yb(OTf)3 worked well, and it was found that other Ln(OTf)3 also catalyzed the above aldol reaction effectively (85-95% yields). 

Herdewijn and collaborators employed a diazo group to introduce the required N=N bond, present in pyridazine-based compounds. The authors reported a new approach to the preparation of new fused pyridazine heterocycles and their derivatives (Scheme 9) (13JOC8745). The first step is an aldol reaction of a-diazo-1,3-diketone 18, yielding /3-hydroxy-a-diazo diketone 19, which is then oxidized with l-hydroxy-l,2-benziodoxol-3(lfi) one 1-oxide (IBX) in acetonitrile imder refluxing conditions to give the... 

Aldol Reactions Addition to Aldehydes and Imines. Since its discovery, the Mukaiyama aldol reaction. has attracted considerable attention and several improvements in reaction conditions have heen reported. Most useful catalysts for this reaction appear to he recently reported lanthanide triflates (eq 5), bis(cyclopentadienyl)titanium bis(trifluoromethanesulfonate), or Cp2Zr(OTf)2 THF. The metallocene salt also catalyzes additions to ketones (eq 6). This reaction can also be carried out under essentially neutral conditions by warming (70 °C) a stoichiometric mixture of the aldehyde and the KSA in acetonitrile (eq 7). When an optically active aldehyde is used, a slightly better stereochemical control is noticed under catalysis of zinc iodide. ... 

Shibasaki and Kanai developed a catalytic enantioselective nitrile aldol reaction using CuOf-Bu-DTBM-SEGPHOS complex as a catalyst (Fig. 3) [27] (for other reports of direct catalytic nitrile aldol reactions, see [31, 32]). Despite moderate enantioselectivity, it is noteworthy that chemoselective generatimi of an enolate equivalent (copper ketene imide 6 in Fig. 4) is possible from acetonitrile in the presence of aldehydes containing more acidic a-protons. The pATa values of a-protons of acetonitrile and aliphatic aldehydes are 31.3 and ca. 23 (in DMSO), respectively. Key for the selective deprotonation from acetonitrile is the chemoselective interaction between soft Cu(I) and soft nitrile, which selectively acidifies a-protons of acetonitrile (Fig. 4, 5). 

In 1971, Hajos and Wiechert independently reported intramolecular desym-metrization cyclization via the aldol reaction. Hajos mentioned that the intramolecular aldol reaction of 2-methyl-2-(3-oxobutyl)-l,3-cyclopentanedione (2) could smoothly afford bicycUc diketone 3 catalyzed by L-proline (1) in N,N-dimethylformamide (DMF), in excellent yield and with 93% ee. Further dehydration of 3 yielded the unsaturated diketone 4 (Scheme 36.1) [5a]. In Wiecherf s work, diketone 4 could be obtained directly from 2 by employing perchloric acid in refluxing acetonitrile (Scheme 36.1) [5bj. 

Ono and coworkers have extended the radical elimination of v/c-dinitro compounds to P-nitro sulfones151 and P-nitro sulfides.138,152 As P-nitro sulfides are readily prepared by the Michael addition of thiols to nitroalkenes, radical elimination of P-nitrosulfides provides a useful method for olefin synthesis. For example, cyclohexanone is converted into allyl alcohol by the reaction shown in Eq. 7.110. Treatment of cyclohexanone with a mixture of nitromethane, PhSH, 35%-HCHO, TMG (0.1 equiv) in acetonitrile gives ahydroxymethylated-P-nitro sulfide in 68% yield, which is converted into the corresponding allyl alcohol in 86% yield by the reaction with Bu3SnH.138 Nitro-aldol and the Michael addition reactions take place sequentially to give the required P-nitro sulfides in one pot. 

In contrast with the reactions of the imino esters, the aldol condensation of imino nitriles and aromatic aldehydes in dichloromethane produces azabutadienes (Scheme 6.17), with the Z-isomers predominating often to the exclusion of the E-isomers [43, 44], Yields generally tend to be at least 10% lower when the reaction is conducted in acetonitrile. 

One-pot conversions of 2-hydroxy(acylbenzenes) with anhydrides or acid chlorides to produce coumarins [52-54] and flavones [54-58] under mild liquiddiquid or solidtliquid two-phase conditions via a Baker-Venkataraman type reaction (Scheme 6.19) are catalysed by quaternary ammonium salts. 3-Substituted coumarins are produced from salicylaldehyde and malonodinitrile, or substituted acetonitriles, in high yield (>85%) in a one-pot catalysed sequential aldol-type reaction and cycliza-tion in the absence of an added organic solvent [59]. When 2 -hydroxychalcones are reduced under catalytic two-phase conditions with sodium borohydride, 2,4-cis-flavan-4-ols are produced [60] (see Section 11.3). 

With PdCl2 (PhCN)2 ZnCl2 in acetonitrile, 4b was found to effect dehydrogenation of 47 at 80°C to give 48. It was concluded that 48 is produced via an aldol-type reaction between 4b and carbonyl compounds, followed by dehydrogenation of the 47 formed as an intermediate (94BCJ2265). 

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