A-Hydroxyacetone

Asymmetric intramolecular hydrosilylation of a-dimethylsiloxyketones (216), which are prepared from a-hydroxyketones 215, catalyzed by [(S ,S )-R-DuPHOS)Rh(COD)]+CF3 SO3-, (219) proceeds smoothly at 20-25 °C to give siladioxolanes 217. Desilylation of 217 affords 1,2-diols 218 with 65-93% ee in good yields (Scheme 22)231. The best result (93% ee) is obtained for the reaction of a-hydroxyacetone using (S, S)-i-Pr-DuPHOS-Rh+ as the catalyst. The same reactions using (S ,S )-Chiraphos and (S)-binap give 218 (R = Me) with 46 and 20% ee, respectively. 

An a-hydroxyacetone oxime anchor (Figure 19.11) has been developed by Haner and coworkers [273] for the phosphoramidite RNA synthesis. The 2 -protected oligoribonucleotides are detached from the respective macroporous polystyrene support (initial loading 30junolg 1) as the 3 -phosphates during 30min of concentrated aqueous ammonia-ethanolic methylamine (1 1 v/v) treatment at 65 °C. The authors have postulated [3-elimination with the formation of 2-nitrosopropene as a plausible mechanism for 3 -phosphate liberation. 

The dipeptide-derived 64 is a suitable aldol reaction catalyst for handling haloacetones and a-hydroxyacetone, and the the water-compatibility of the analogous 65 underscores its utility in the reaction involving a,a -dihydiDxyacetone. ... 

Generally a high excess of ketone was used in all these processes. This was not an economical or practical problem when simple and volatile ketones were used as nucleophiles, but could be a severe drawback when more sophisticated ketones were used. The use of ionic liquid such as l-ethyl-3-methyl-l//-imidazolium trifluo-romethanesulfonate ([emim][OTf]) [25] has allowed to reduce the amount of ketones used. Thus, the reaction of a-hydroxyacetone (8a R = H), as well as a-methoxy-acetone (8c R =Me) with p-(trifluoromethyl)benzaldehyde derivatives gave a mixture of three possible isomers of type 9 and 10 with mediocre diastereoselectivities (no enantioselectivities were reported). Under this reaction conditions, a-chloro-(11a) and a-fluoroacetone (lib) were used as source of nucleophile (Scheme 4.4),... 

The other substrates with different electron-withdrawing substituents such as a-hydroxyacetone, a-acetoxyacetophenone, and phenyl glyoxal monohydrate are completely inert to Alpine-Borane. Unlike a-ketoesters, the P-ketoesters react very slowly, e.g., reduction of ethylacetoacetate with 100% excess of neat Alpine-Borane takes 3-5 days for completion, with 50.6% asymmetric induction. 

C. Wu, X. Fu, S. Li, Tetrahedron Asymmetry 2011, 22, 1063-1073. Simple and inexpensive threonine-based organo-catalysts for the highly diastereo- and enantioselective direct large-scale syn-aldol and anti-Mannich reactions of a-hydroxyacetone. 

Allyl alcohol is oxidized by aqueous [PdClJ to jS-hydroxypropanol, a-hydroxyacetone, and acrolein (CH2 = CHCHO), or propanol. Deuterium labeling was used to show that acrolein does not result from dehydration of HOCH2CHCHO, but is a direct oxidation product. Most probably the C=C bond as well as the OH group are coordinated to the metal.The... 

Following immediately the initial efforts on primary amino acids catalyzed aldol reactions, the application of primary amine acid in Mannich reaction has also been attempted. Cordova reported that simple primary amino acids and their derivatives could catalyze the asymmetric Mannich reactions of ketones with comparable results to those obtained in the catalysis of proline[28]. Later, Barbas [29] and Lu [30] independently reported that L-Trp or 0-protected L-Thr could catalyze anti-selective asymmetric Mannich reactions of a-hydroxyacetones with eiflier preformed or in-situ generated imines. The preference of anii-diastereoselectivity was ascribed to the formation of a Z-enamine, with the assistance of an intramolecular H-bond (Scheme 5.15). 

After cleavage the reaction mass is a mixture of phenol, acetone, and a variety of other products such as cumylphenols, acetophenone, dimethyl-phenylcarbinol, a-methylstyrene, and hydroxyacetone. It may be neutralised with a sodium phenoxide solution (20) or other suitable base or ion-exchange resins. Process water may be added to facilitate removal of any inorganic salts. The product may then go through a separation and a wash stage, or go direcdy to a distillation tower. 

The yield of acetone from the cumene/phenol process is beUeved to average 94%. By-products include significant amounts of a-methylstyrene [98-83-9] and acetophenone [98-86-2] as well as small amounts of hydroxyacetone [116-09-6] and mesityl oxide [141-79-7]. By-product yields vary with the producer. The a-methylstyrene may be hydrogenated to cumene for recycle or recovered for monomer use. Yields of phenol and acetone decline by 3.5—5.5% when the a-methylstyrene is not recycled (21). 

Oxidation of a glycol can lead to a variety of products. Periodic acid quantitatively cleaves 1,2-glycols to aldehydes and is used as an analysis method for glycols (12,13). The oxidation of propylene glycol over Pd/C modified with Pb, Bi, or Te forms a mixture of lactic acid, hydroxyacetone, and pymvic acid (14). Air oxidation of propylene glycol using an electrolytic crystalline silver catalyst yields pymvic aldehyde. 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

Hydroxyl groups are stable to peracids, but oxidation of an allylic alcohol during an attempted epoxidation reaction has been reported." The di-hydroxyacetone side chain is usually protected during the peracid reaction, either by acetylation or by formation of a bismethylenedioxy derivative. To obtain high yields of epoxides it is essential to avoid high reaction temperatures and a strongly acidic medium. The products of epoxidation of enol acetates are especially sensitive to heat or acid and can easily rearrange to keto acetates. 

Similar hydroxylation-oxidations can be carried out using a catalytic amount of osmium tetroxide with A-methylmorpholine oxide-hydrogen peroxide or phenyliodosoacetate." A recent patent describes the use of triethylamine oxide peroxide and osmium tetroxide for the same sequence. Since these reactions are of great importance for the preparation of the di-hydroxyacetone side-chain of corticoids, they will be discussed in a later section. 

Figure 10.25 Inverted approach for aldose synthesis using FruA catalysis, and application ofthe strategy for deoxysugar synthesis based on a phosphorothioate analog synthesis of 1-deoxysugars by FSA catalyzed addition of hydroxyacetone.

Product Acceptors. Many enzyme assays use acceptors, as for instance 2-ethylaminoethanol and other aminated alcohols iihich act as acceptors for the phosphoryl product of the reaction catalyzed by alkaline phosphatase (25) (Fig. 4). Hydroxylamine can act as an acceptor for the hydroxyacetone produced by eno-lase and semicarbazide can act as an acceptor for the pyruvate produced by LD. It is necessary to optimize the concentration of such an acceptor before using it routinely as often what may be a theoretically desirable acceptor is in practice superfluous. 

Alternative reducing agents are still sometimes proposed and evaluated. A detailed comparison of five reducing agents has been reported sodium dithionite, thiourea dioxide, iron(II) chloride/gluconic acid, sodium hydroxymethanesulphinate and hydroxyacetone [123]. Results of fastness tests on black polyester dyeings variously aftertreated are given in Table 12.10. 

COD values for hydroxyacetone are after treatment in a bioreactor such treatment is not possible with dithionite. 

R)-l,2-Propanediol is an intermediate for (S)-oxafloxazin, a bactericide which until recently was sold as a racemate. The (R)-diol is now produced by Takasago via hydrogenation of hydroxyacetone (see Fig. 37.23) using a Ru-Tol-binap catalyst on a 50 t y 1 scale [92 b[. Recently, it was reported that segphos - a newly developed biaryl diphosphine - shows even better results, achieving >98% ee and TON and TOF of 10000 and 1400 h, respectively [16, 93]. 

At even higher temperature, the polysaccharides decompose further by extensive C-C bond breaking. This leads to the formation of C2 4 oxygenates such as glycol aldehyde, acetic acid and hydroxyacetone (CH3-CO-CH2OH). The formation of these products can be rationalized by a series of reactions that include,... 

Furthermore, a base-catalyzed transformation by OH from the reaction medium between glycerate and hydroxypyruvate aldehyde (or hydroxypyruvic acid) could be excluded, while hydroxyacetone and glyceraldehyde interconversion was possible (Scheme 11.11). The existence of two major routes, of which hydroxyacetone and glyceric aldehyde are the primary oxidation products and glycolic and oxalic acid are the end-members, respectively, is now firmly established. Clearly, rapid oxidation of glyceraldehydes favors glyceric acid rather than hydroxyacetone formation. 

The scheme also indicates that high glyceric acid selectivity is obtainable either via a selective catalyst for glyceraldehydes formation, or with a less selective catalyst in basic medium, where the hydroxyacetone-glyceric aldehyde equilibration is established. 

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