Aldehydes acetyl formation

Liquid absorption is a common technique for enriching compounds in reactive liquids like solutions of dinitrophenylhydrazine (DNPH) (for aldehydes), acetyl acetone (for formaldehyde) or aqueous carbonate solutions (for organic acids), both procedures which combine trapping and derivatization of the target compound. Another possibility is the use of dissolved alkali or acids to trap certain substances by the formation of salts in the solution. 

Attempts to use acetic-formic anhydride with Friedel-Crafts catalysts resulted only in acetylation. However, using anhydrous HF as a catalyst, a small amount of aldehyde is also formed in accordance with the fact that acetic—formic anhydride gives both acetyl and formyl fluoride with HF. By continuous removal of the low boiling HCOF, the reaction can be shifted to the formation of this compound (118). 

The formation of optically active acyloins is also catalyzed by the yeast Candida Pareri if the bacteria Zymomonas mobilis and Zymomonas carlbergensis42 and the fungus Diplodia gossypina43. The latter microorganism produces (3/ ,66 )-6-hydroxy-7-oxo-8-norcitronellene from (/ )-citronellene by a reaction sequence that converts (7d)-citronellene to (/ )-4-methyl-5-butenal followed by addition of the acetyl moiety to the / e-face of the aldehyde. 

N-Acetylneuraminic acid aldolase (or sialic acid aldolase, NeuA EC 4.1.3.3) catalyzes the reversible addition of pyruvate (2) to N-acetyl-D-mannosamine (ManNAc (1)) in the degradation of the parent sialic acid (3) (Figure 10.4). The NeuA lyases found in both bacteria and animals are type I enzymes that form a Schiff base/enamine intermediate with pyruvate and promote a si-face attack to the aldehyde carbonyl group with formation of a (4S) configured stereocenter. The enzyme is commercially available and it has a broad pH optimum around 7.5 and useful stability in solution at ambient temperature [36]. 

Compared to the cyclic ketones, the coupling of aliphatic aldehydes to prepare 3-substituted indoles was less successful, except for phenyl acetaldehyde, which afforded 3-phenyl indole 83 in 76% yield (Scheme 4.22). The lack of imine formation or the instability of the aliphatic aldehyde towards the reaction conditions may be responsible for the inefficiency of these reactions. Therefore, a suitable aldehyde equivalent was considered. With the facile removal of a 2-trialkylsilyl group from an indole, an acyl silane was tested as a means of preparing 3-substituted indoles. Indeed, coupling of acetyl trimethylsilane with the iodoaniline 24 gave a 2 1 mixture of 2-TMS-indole 84 and indole (85) in a combined 64% yield. Evidently, the reaction conditions did lead to some desilylation. Regardless, the silyl group of 84 was quantitatively removed upon treatment with HC1 to afford indole (85). 

Production of acetate ester pheromone components utilizes an enzyme called acetyl-CoA fatty alcohol acetyltransferase that converts a fatty alcohol to an acetate ester. Therefore, alcohols could be utilized as substrates for both aldehyde and acetate ester formation. In some tortricids an in vitro enzyme assay was utilized to demonstrate specificity of the acetyltransferase for the Z isomer of ll-14 OH [66]. This specificity contributes to the final ratio of... 

The amidocarbonylation of aldehydes provides highly efficient access to N-acyl a-amino acid derivatives by the reaction of the ubiquitous and cheap starting materials aldehyde, amide, and carbon monoxide under transition metal-catalysis [1,2]. Wakamatsu serendipitously discovered this reaction when observing the formation of amino acid derivatives as by-products in the cobalt-catalyzed oxo reaction of acrylonitrile [3-5]. The reaction was further elaborated to an efficient cobalt- or palladium-catalyzed one-step synthesis of racemic N-acyl a-amino acids [6-8] (Scheme 1). Besides the range of direct applications, such as pharmaceuticals and detergents, racemic N-acetyl a-amino acids are important intermediates in the synthesis of enantiomeri-cally pure a-amino acids via enzymatic hydrolysis [9]. 

Zirconium tetrachloride promotes a tandem nucleophilic addition and aldol-type condensation reaction of methyl propynoate, or /V,/V-dimethylpropynamidc, with aldehydes, or ketones, in the presence of tetra-n-butylammonium iodide (Scheme 6.13) [8] with a high selectivity towards the formation of Z-isomers. A similar reaction occurs between aliphatic and aromatic aldehydes and penta-3,4-dien-2-one to yield 1-substituted 2-acetyl-3-iodobut-3-enols (50-75%) [9]. 

The low-temperature hydrocarbon oxidation mechanism discussed in the previous section is incomplete because the reactions leading to CO were not included. Water formation is primarily by reaction (3.56). The CO forms by the conversion of aldehydes and their acetyl (and formyl) radicals, RCO. The same type of conversion takes place at high temperatures thus, it is appropriate, prior to considering high-temperature hydrocarbon oxidation schemes, to develop an understanding of the aldehyde conversion process. 

Curiously, however, reaction of the dialdehyde (94b) with ethyl nitroacetate under practically identical conditions — aqueous ethanol in the presence of sodium acetate and sodium carbonate at pH 8.6 — takes a different course. The compound, isolated in 34% yield, constitutes a monoaddition product to one aldehyde group, as evidenced by the formation of a triacetate after hydrogenation and acetylation. It has been assigned structure (95) 5 ) and, as such, is a C-substituted derivative of the hemialdal form (94a) of the dialdehyde. Though some NMR data were cited as proof of this formulation 58) two alternatives, (96) and (97) respectively, cannot be ruled out. Of these, structure (97) derived from... 

Cyanation of aldehydes and ketones is an important chemical process for C C bond formation." " Trimethylsilyl cyanide and/or HCN are commonly used as cyanide sources. The intrinsic toxicity and instability of these reagents are problematic in their applications. Acetyl cyanide and cyanoformates were used as cyanide sources in the enantioselective cyanation of aldehydes catalyzed by a chiral Ti complex and Lewis base (Scheme 5.31)." The Lewis base was necessary for the good yields and selectivities of these reactions. The desired products were obtained in the presence of 10mol% triethyl amine and 5mol% chiral titanium catalyst (Figure 5.14). Various aliphatic and aromatic aldehydes could be used in these reactions. 

Another stereoselective synthesis (Scheme 11) is based on sugar aldehyde 35 and intermediate 36 subsequent 1,2-O-isopropylidine deprotection, N,0-debenzylation/olefin reduction/reductive cyclization in a single pot, and O-acetylation result in the formation of bicyclic aza sugar 37 (09TA1217). 

Minisci and coworkers followed Ishii s procedure, and implemented it in the oxidation of benzyhc alcohols to benzaldehydes in almost quantitative yields" (Table 12). A,Af-dimethylbenzylamines were converted into aldehydes in good yields, by using catalytic amounts of either HPI or A-hydroxysuccinimide (HSI) for the formation of the corresponding aminoxyl radical intermediates. Because the attempted oxidation of primary and secondary amines caused the degradation of catalyst HPI, protection of the amino group in those substrates by acetylation was considered. This led one to develop... 

The formation of the diacetamide derivatives requires, in this theory, the existence of two acetyl groups so located in the molecule, that they can react, through the ammonia, with the aldehyde carbon. 

Reaction at the C atom of nitronate salts is known with a variety of electrophiles, such as aldehydes (Henry reaction) and epoxides (191-193). Thus the incorporation of the nitro moiety and the cyclization event can be combined into a tandem sequence. Addition of the potassium salt of dinitromethane to an a-haloaldehyde affords a nitro aldol product that can then undergo intramolecular O-alkylation to provide the cyclic nitronate (208, Eq. 2.17) (59). This process also has been expanded to a-nitroacetates and unfunctionalized nitroalkanes. Other electrophiles include functionalized a-haloaldehydes (194,195), a-epoxyaldehydes (196), a-haloenones (60), and a-halosulfonium salts (197), (Chart 2.2). In the case of unsubstituted enones, it is reported that the intermediate nitronate salt can undergo formation of a hemiacetal, which can be acetylated in moderate yield (198). 

A branched-chain iodo sugar derivative, l,5-anhydro-4,6-0-benzyl-idene-2,3-dideoxy-3-C-(iodomethyl)-D-rifoo-hex-l-enitol [4,6-O-ben-zylidene-3-deoxy-3-C-(iodomethyl)-D-allal] (200), is one of the products formed on treatment of methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-en/thro-hex-2-enopyranoside (77) with the Simmons-Smith reagent (diiodomethane and zinc-copper couple).123,212 Compound 200 displays high solvolytic reactivity, an observation that has been rationalized by supposing the formation of the highly stabilized carbonium ion213 (201). Thus, under conditions wherein methyl 2,3,4-tri-0-acetyl-6-deoxy-6-iodo-a-D-glucopyranoside required more than 24 hours to react appreciably with an excess of silver nitrate in 50% aqueous p-dioxane buffered with silver carbonate, the iodide 200 was hydrolyzed completely in less than 1 minute the product of hydrolysis of 200 is the cyclopropyl aldehyde 202. Methanolysis of... 

Aliphatic aldehydes react to form monoalkylidene derivatives only in presence of potassium r-butoxide. A mechanism has been postulated that also explains the observed N-deacetylation during the formation of the product. The essential step in this is the intramolecular N - O acetyl migration in the initially formed aldol. Subsequent protonation and elimination of the acetoxy group lead to the product (Scheme 26). 

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