Keto aldehydes hydration

High-quality albuterol was obtained in good yield from this process. However, several environmental disadvantages were identified. The preparation of the keto aldehyde hydrate (KAH) generated dimethyl sulfide, methyl bromide, and trimethyl-sulfonium bromide (this compound sublimed in the condenser). In addition, reduction of the Schiff base with dimethylsulfide borane, although very attractive in simplifying... 

Reaction of a-diazo ketones with DDO leads to a-keto aldehyde hydrates (eq 24). Oximes are converted to the free ketones by DD0.3 ... 

Si. rra(pentafluorophenyl)boron was found to be an efficient, air-stable, and water-tolerant Lewis-acid catalyst for the allylation reaction of allylsilanes with aldehydes.167 Sc(OTf)3-catalyzed allylations of hydrates of a-keto aldehydes, glyoxylates and activated aromatic aldehydes with allyltrimethylsilane in H2O-CH3CN were examined. a-Keto and a-ester homoallylic alcohols and aromatic homoallylic alcohols were obtained in good to excellent yields.168 Allylation reactions of carbonyl compounds such as aldehydes and reactive ketones using allyltrimethoxysilane in aqueous media proceeded smoothly in the presence of 5 mol% of a CdF2-terpyridine complex (Eq. 8.71).169... 

Methyl and methylene groups adjacent to carbonyl groups are easily oxidized to carbonyls to yield a-keto aldehydes or a-diketones. The reagent of choice is selenium dioxide or selenious acid. The reaction is catalyzed by acids and by acetate ion and proceeds through transition states involving enols of the carbonyl compounds [518]. The oxidation is carried out by refluxing the ketone with about 1.1 mol of selenium dioxide in water, dilute acetic acid, dioxane, or aqueous dioxane [517]. The byproduct, black selenium, is filtered off, but small amounts of red selenium sometimes remain in a colloidal form and cannot be removed even by distillation of the product. Shaking the product with mercury [523] or Raney nickel [524] takes care of the residual selenium. The a-dicarbonyl compounds are yellow oils that avidly react with water to form white crystalline hydrates (equations 407 and 408). 

Indirect electrooxidation of cyclic aziridines using NaCl or NaBr as a redox catalyst results in C(l)-C(2) bond cleavage under formation of the corresponding keto nitriles. This reaction is explained by the intermediate generation of an azaallenyl cation, which is hydrated to the o -hydroxyimine. Further oxidation by Cl" then would lead to the open-chain keto A-chloroimine, which by HCl elimination forms the keto nitrile, while its hydrolysis leads to the keto aldehyde as a side product [32] ... 

The Swern oxidation proceeds rapidly at low temperatures and thus can be employed for the preparation of a-keto aldehydes and acylsilanes, which are hyperactive carbonyl compounds and prone to hydration, polymerization, and air oxidation. ... 

A new approach to the 5-keto-aldehydes frequently employed as spiro-system precursors utilizes the known regiospecific hydration of acetylenic ketones. Thus the acetylenic aldehyde (167), produced by alkylating the t-butylimine (166) with trimethylsilylpropargyl bromide, underwent simultaneous regiospecific hydration and deprotection to (168) on treatment with mercuric sulphate in aqueous THF containing a trace of H2S04. ° ... 

Step 6 is the final step in the cellulose-to-lactic acid cascade, involving the isomerization of the 2-keto-hemi-acetal (here pyruvic aldehyde hydrate) into a 2-hydroxy-carboxyhc acid. This reaction is known to proceed in basic media following a Cannizzaro reaction with 1,2-hydride shift [111], Under mild conditions, Lewis acids are able to catalyze this vital step, which can also be seen as an Meerwein-Ponndorf-Verley reduction reaction mechanism. The 1,2-hydride shift has been demonstrated with deuterium labeled solvents [110, 112], Attack of the solvent molecule (water or alcohol) on pymvic aldehyde (step 5) and the hydride shift (step 6) might occur in a concerted mechanism, but the presence of the hemiacetal in ethanol has been demonstrated for pyruvic aldehyde with chromatography by Li et al. [113] andfor4-methoxyethylglyoxal with in situ CNMRby Dusselier et al. (see Sect. 7) [114]. 

All the preceding substrates, even oxyheme, are expected to form carbanions readily. In fact, under solution conditions, in a mixture of f-butanol, dimethylformamide and base, the indole and flavonol derivatives undero oxygenation biomimetically to cleave the C-2, C-3 bond. Like indole itself, the C-3-substituted indoles, on enzymic catalysis, are structurally pre-disposed to yield tetrahedral carbanionic centers at C-3, suitably soft for easy and efficient addition to triplet dioxygen 139). The resulting peroxide (53) (Scheme 24) could possibly cleave its C-2, C-3 bond by the expedient of hydration (54) followed by cleavage to the keto-aldehyde (55). 

Reaction with Hydrates ofa-Keto Aldehydes and Glyoxylates. Catalytic allylations of the hydrates of a-keto aldehydes and glyoxylates with allyltrimethylsilane can be performed by using Yb(OTf)3 and Sc(OTf)3 (eq 26). TMSOMs, which is formed in situ from methansulfonic acid and allyltrimethylsilane, is also a viable catalyst for this reaction. ... 

In an aqueous solution, a ketone or an aldehyde is in equilibrium with its hydrate, a geminal diol. With most ketones, the equilibrium favors the unhydrated keto form of the carbonyl. 

Isoleucine and valine. The first four reactions in the degradation of isoleucine and valine are identical. Initially, both amino acids undergo transamination reactions to form a-keto-/T methyl valerate and a-ketoiso valerate, respectively. This is followed by the formation of CoA derivatives, and oxidative decarboxylation, oxidation, and dehydration reactions. The product of the isoleucine pathway is then hydrated, dehydrogenated, and cleaved to form acetyl-CoA and propionyl-CoA. In the valine degradative pathway the a-keto acid intermediate is converted into propionyl-CoA after a double bond is hydrated and CoA is removed by hydrolysis. After the formation of an aldehyde by the oxidation of the hydroxyl group, propionyl-CoA is produced as a new thioester is formed during an oxidative decarboxylation. 

Organic bases such as tetraalkylammonium hydroxides, tertiary amines, and phosphines [46,49,52-54] were employed as additives to improve the activity and selectivity of platinum catalysts in the oxidation of L-sorbose to 2-keto-L-gulonic acid (2-KLG). Rate acceleration was attributed to a beneficial effect of the amine on the hydration of the intermediate aldehyde. The selectivity enhancement obtained with hexamethylenetetramine (HMTA) was attributed to a steric effect involving a complex between HMTA and L-sorbose via hydrogen bonding [52] (see Section 9.3.3.2). 

Diazepines.—Formation. There is a report on the formation of the C=N bond in l,4-benzodiazepin-2-ones and in l,2-dihydropyrazin-2-ones by the intramolecular reaction of aldehyde groups or keto-groups with iminophos-phoranes the process had earlier been described in the patent literature. 1,4-Benzodiazepin-2-ones have also been prepared from indoles by ozonolysis followed by reductive cyclization with hydrazine hydrate. A new simple syn-... 

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