Hexofuranose reactions

Di-0-isopropylidene-a-D-rtbo-hexofuranos-3-ulose (100) was treated with (chlorofluoromethylene)triphenylphosphorane (prepared by reaction of triphenylphosphine on difluorocarbene generated in situ by reaction of potassium ferf-butoxide with dichloro-fluoromethane), to give cis- and rans-3-C-(chlorofluoromethylene)-3-deoxy-l,2 5,6-di-0-isopropylidene-a-D-ribo- (101 and 103) and -xyfo-hexofuranoses (105 and 107), which, on treatment with lithium aluminum hydride, gave cis- and frans-3-deoxy-3-C-(fluoromethyl)-1,2 5,6-di-O-isopropylidene-a-D-rtbo- (102 and 104) and -xyZo-hexofura-... 

The addition of iodine trifluoroacetate (produced by reaction of iodine with silver trifluoroacetate) to unsaturated carbohydrates has been investigated.134 Treatment of 5,6-dideoxy-l,2-0-isopropylidene-a-D-xylo-hex-5-enofuranose (89) with silver trifluoroacetate and iodine in acetonitrile gave 3,6-anhydro-5-deoxy-5-iodo-l,2-0-iso-propylidene-a-D-gluco(and /3-L-ido)furanose (91) and 5-deoxy-5-iodo-l,2-0-isopropylidene-6-0-(trifluoroacetyl)-o -D-gluco(and/or /3-L-ido)-furanose (92), with the former preponderating. Component 91 was converted into 3,6-anhydro-5-deoxy-l,2-0-isopropylidene-a-D-xj/io-hexofuranose (94) by hydrogenation over Raney nickel (see also, Section III,3 p. 299), and component 92 was converted into 5-deoxy-l,2-0-isopropylidene-a-D-xy/o-hexofuranose (95) by treat-... 

The formation of the pyridinol is prevented if, in the step 19 to 20, no anion can be eliminated from C-3 this is the case with 5-amino-3,5-dideoxy-l,2-0-isopropylidene-a-D-er /thro-pentofuranose, which, on acid hydrolysis, afFords only the Amadori rearrangement product and no pyridine derivative. The reaction then proceeds, according to the above mechanism, in only one direction from 19. The 3-deoxypentose is prepared, in a manner analogous to the formation of 15, from 3-deoxy-l,2-0-isopropylidene-a-D-riho-hexofuranose through catalytic reduction of the phenylhydrazone of its periodate-oxidation product. ... 

Other studies of selective sulfonylation at a primary hydroxyl group of sugars were made with 5-deoxy-l,2-0-isopropylidene-a-D-xy/o-hexofuranose at —12° to give the 6-p-toluenesulfonate and 6-methanesulfonate. On wanning the reaction mixture to 25°, these derivatives were converted into 3,6-anhydro-5-deoxy-l,2-0-isopropyl-idene-a-D-xyio-hexofuranose. The formation of 2,5-anhydrides on p-toluenesulfonylation of dialkyl dithioacetals of pentoses probably proceeds similarly, through the 5-p-toluenesulfonates. 

In general, on reaction with lithium aluminum hydride, secondary sulfonic esters are desulfonylated, with formation of the corresponding secondary alcohol. An exception is provided in an observation by Reist and coworkers, who treated 6-0-benzoyl-l,2-0-isopropyli-dene-5-O-p-tolylsulfonyl-a-D-glucofuranose, with lithium aluminum hydride in ether and obtained a product thought to be 6-deoxy-l,2-0-isopropylidene-y3-L-idofuranose, derived from an intermediate 5,6-anhydro-L-ido derivative later, Ryan and coworkers showed, from its nuclear magnetic resonance spectrum, that the product was 5-deoxy-l,2-0-isopropylidene-a-D- t/Zo-hexofuranose. The problem has been re-examined by Overend and coworkers the repetition experiment under the conditions of Reist and coworkers afforded 5-deoxy-... 

The stereoselective five-ring annulation is the cornerstone in a synthesis of Corey s lactone, starting from readily available 3-deoxy-1.2 5,6-di-0-isopropylidene-a-D- v7)o-hexofuranose (8)54. Treatment of the intermediate 5-hexenol with thiocarbonylbis(iniidazole) followed by reaction with tributyltin hydride (Barton deoxygenation) gives exclusively the bicyclic compound 9 with the /i-orientated methoxymcthvl substituent. The cyelization product has the correct absolute configuration for the Corey lactone, to which it can be converted in four additional steps. 

The 1,2-0-isopropylidenehexofuranose 5,6-trithiocarbonates undergo desulfurization with Raney nickel in the same manner as do the 5,6-episulfide analogs, with the formation of 5,6-dideoxy-l, 2-0-isopropylidene- t-D-a 2/Zo-hexofuranose (90). The 5,6-episulfides polymerize in aqueous alkali, presumably by a sequential, episulfide-cleavage reaction caused by thiolate anion and, for example, compound (84) gives a polymer, formu-... 

Similar transformations are useful in determining the nature of hep-toses (either before " or after methylation), for demonstrating the existence of hexofuranose units in a polysaccharide, and for studying the products obtained from amino sugars by reaction with ninhydrin. ... 

A vast majority of the amino derivatives used as substrates in the synthesis of carbohydrate aziridines are A-substituted, mostly as A-acylamines or A-aryl(alk-yljsulfonylamines. Reaction of free amines has rarely been reportedin the carbohydrate field and difficult and incomplete cyclization was generally encountered. Paulsen and Stoye, however, reported spontaneous cyclization of 6-hydrazino-5-C-mesyl-D-hexofuranoses, obtained from 5,6-di-C-mesyl-hexofura-noses by treatment with hydrazine, into the A-amino-5,6-epimino derivatives." ... 

Branched-chain sugars. The reaction of l,2 5,6-di-0-isopropylidene-a-D-hexofuranose-3-ulose (2) with this reagent (1) in THF at — 65° gives the adduct 3, which can be converted as shown into branched chain sugars as formulated in scheme (I), shown on page 332. 

Cyclization of 5,6-dideoxv-6-nitro-D-xylo-hexofuranose led to a mixture of myo- and epi-isomers (43) which were separated and converted to the corresponding amino compounds.Examples of the use of the Ferrier reaction for preparing cyclitols and amino-cyclitols from D-glucose and D-glucosamine have been published, e.g., (44)- (45).52... 

Tadano [104] used the same reaction for the introduction of a quaternary stereo-genic carbon atom in hexofuranoses 429 and 432. As in the preceding study, configuration of the allylic alcohol double bond played a cmcial role for both yield and diastereoselectivity. Thus, alcohol (E)-429 afforded a mixture of esters 430 and 431, whereas alcohol (Z)-429 gave rise exclusively to ester 430. The same behavior was observed with alcohols ( )- and (Z)-432 (Scheme 6.71). 

It has been postulated that it may participate in the hexokinase reaction in either of two ways (1) by activating the conversion of the hexopy ranose form to hexofuranose, or (2) by mediating a hexokinase-hormone complex. 

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