L-allose

L-Allose phenylosazone, prepared from L-psicose, was decomposed by benzaldehyde to L-allosone, which was converted into L-alloascorbic acid.187... 

Silyl enol ether 139 has also been transformed into D-allose, as shown in Scheme 5. The same methods can be applied to the enantiomeric enol ether derived from camphanate 38, and this allows one to prepare L-allose and its derivatives. Oxidation of 139 with MCPBA in THF (20 °C) led to the product of epoxide acidolysis 147 (69 %) which yielded 148 on heating to 200 °C for 15 min. Addition of 1.1 equiv. of MCPBA converted 148 into lactone 149 which in the presence of MeOH and K2CO3 (20 °C), gave selectively diester 150. Reactions 147... 

The exo/endo (99 1) adducts are of 90-92% optical purity. The enantiomeric bicyclic ketones can be transformed into carbohydrates in a few, stereochemically well-defined steps. In this way, derivatives of d- and L-ribose [38], L-allose, L-talose, and such [39] have been obtained. 

Figure 6A.4. Synthetic route to L-allose illustrating a reiterative two-carbon extension cycle (a) (CH30)3P(0)CHC00CH3, (b) DIBAL, (c) (+)-DET/Ti(0-i-Pr)4, (d) PhSH/OH , (e)...

On the other hand, 32 was first transformed into the 3,5-dinitrobenzoate 45 which allowed diastereoselective dihydroxylation20 to give 46 after methanolysis and benzylation. 46 afforded the hemiacetal 47 from which L-allose via route A and D-allose via route B were obtained (Scheme 13).16... 

Crystalline L-altrose was described in 1934 by Austin and Humoller. After improving the methods for the preparation of L-ribose," they applied the cyanohydrin synthesis to 30 g. of that sugar and obtained 17 g. of crystalline calcium L-altronate and 14.5 g. of crystalline L-allono-7-lactone. Reduction of the latter with sodium amalgam yielded crystalline L-allose. The calcium L-altronate, by appropriate reactions, was converted to L-altrose, and the last of the sixteen theoretically possible aldohexoses had been prepared. Data on L-altrose and its derivatives are included in Table I. 

From L-allulose Steiger " prepared the phenylosazone (L-allose phenyl-osazone), which was hydrolyzed to L-allosone (LXIV) by means of benzaldehyde. The addition of hydrocyanic acid to the osone, followed by saponification with hydrochloric acid, then yielded crystalline l-alloascorbic acid (LXV), of m. p. 177° (decomp.) and - -29.3° in... 

Auberson, Y, Vogel, P, Total synthesis of L-allose, L-talose, and derivatives, Helv. Chim. Acta, 72, 278-286, 1989. 

Combining the D-erythrose derivative 26 obtained by L-proline-catalyzed dimerization of (t-Bu)Ph2SiOCH2CHO with enoxysilane 27 in Mukaiyama aldol reactions catalyzed by various Lewis acid, MacMillan and co-workers have realized efficient, two-step syntheses of semi-protected D-glucose (28G), L-mannose (28M) and L-allose (28A) (O Scheme 23) [148]. Using D-proline to generate tetrose 29 and its condensation with 27b, the semi-protected D-glucose derivative 30 was obtained in two steps [149]. 

Cordova and co-workers have studied the double aldol reaction of benzyloxyacetaldehyde using various a-aminoacids as catalysts. With L-proline and hydroxy-L-proline a tetrose and the L-allose derivative 33 were obtained in 41 and 28% yield, respectively, and with an enantiomeric excess higher than 98% (O Scheme 26). As expected, with D-proline as catalyst, the corresponding D-allose derivative was obtained with the same ease in a one-pot operation [151]. 

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