Hexofuranose 1.2- 0-isopropylidene

The mass spectra of methyl 3-deoxy-p-v-tkreo-pentopyrano-side, methyl 4-deoxy-j3-T>-thieo-pentopyranoside, and 5-deoxy-fi-D-xylo-furanoside are discussed and compared fragmentation paths are sufficiently different to allow identification on the basis of their mass spectra. On the other hand, the mass spectra of methyl 2- and 3-deoxy-5-O-methyl-f3-i>-erythro-pentofuranosides do not exhibit fragmentation differences. The mass spectra of 3-deoxy-l,2 5,6-di-O-isopropylidene -d-xylo - hexofuranose, 5- deoxy -1,2-0-isopropylidene-D-xy o-hexofuranose, and 6-deoxy-l,2-0-iso-propylidene-D-glucofuranose show prominent differences, even between the 5- and 6-deoxy isomers. The interpretation of the spectra was aided by metastable-ion peaks, mass spectra of DzO-exchanged analogs, and the mass spectrum of an O-isopropylidene derivative prepared with acetone-d6. 

The remaining derivatives, 3-deoxy-l,2 5,6-di-0-isopropylidene-D-xt/Zo-hexofuranose (34,39) (9) and 5-deoxy-l,2-0-isopropylidene-D-xt/Zo-hexofur-anose (23, 41) (11), together with the previously mentioned 10 comprise... 

Figure 8. Mass spectrum of 5-deoxy-l,2-0-isopropylidene-T>-xy o-hexofuranose...

In the mass spectrum (Figure 8) of the corresponding ketal of 5-deoxy-D-xt/Zo-hexose, 5-deoxy-l,2-0-isopropylidene-D- rt/Zo-hexofuranose (11), the peak from C-4-C-5 cleavage, m/e 159, is of minor relative intensity. Since the ions at m/e 159 are the same from both isomers, 10 and 11, the intensity difference must be attributable to the lower stability of the primary radical formed from C-5 of 11 compared with the secondary radical from 10 ... 

The potentialities of this method are such that, with the proper choice of hexofuranose derivative, access can be gained to 2,5-anhydroaldoses in which the side chains have the cis orientation, as would be required for further elaboration into C-nucleosides. Matsui and coworkers62 reported the synthesis of modified C-nucleosides by acidic treatment of 3-0-benzyl-l,2-0-isopropylidene-5,6-di-0-(methylsulfonyl)-/3-L-talofuranose (60), to give 2,5-anhydro-3-0-benzyl-6-0-(methylsulfonyl)-aidehydo-D-allose dimethyl acetal (61). 

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-... 

Carbapentofuranoses could be obtained by periodate cleavage of an exocyclic diol in the isopropylidene protected carba hexofuranoses, as illustrated for 72. The protected carba pentofuranose 75 was obtained and deprotected to give carba- -D-lyxofuranose (76). 

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-... 

An investigation of the reduction of chlorodeoxy sugars with lithium aluminum hydride has been reported.68 In one experiment, 3-deuterio-l,2 5,6-di-0-isopropylidene-a-D-allofuranose (197) was prepared, and converted into 3-chloro-3-deoxy-3-deuterio- l,2 5,6-di-0-isopropyl-idene-a-D-glucofuranose (198) by treatment with triphenylphos-phine-carbon tetrachloride reduction with lithium aluminum hydride gave 3-deoxy-3-deuterio-1,2 5,6-di-O-isopropylidene-a-D-r/foo-hexofuranose (199), a result which established that the reduction must have occurred with, retention of configuration at C-3. 

Anhydro-3-deoxy-l,2-0-isopropylidene-a-D-x //o-hexofuranose— 3-deoxy-D-x /io-hexose 6-phosphate.207... 

Deoxy-l,2 5,6-di-0-isopropylidene-a-D-r1bo-hexofuranose D-ribo-Hexofuranose, 3-deoxy-l,2 5,6-di-0-isopropylidene, a- (8) a-D-ribo-Hexofuranose, 3-deoxy-l,2 5,6-bis-0-(l-methylethyliderie)- (9) (4613-62-1) l,2 5,6-Di-0-isopropylidene-a-D-glucofuranose Glucofuranose, l,2 5,6-di-0-isopropylidene, a-D- (8) a-D-glucofuranose, 1,2 5,6-bis-0-(1-methyl -ethylidene)- (9) (582-52-5)... 

S. Iacono and James R. Rasmussen 57 DEOXYGENATION OF SECONDARY ALCOHOLS 3-DE0XY-l,2 5,6-DI-0-ISOPROPYLIDENE-a-D-ribo-HEXOFURANOSE... 

Hydrogenation of 78 in ethanol in the presence of Raney nickel (W-4) for 2 days at room temperature did not produce the anticipated 5-deoxy-5-C-(phosphinyl)hexofuranose 84 but, instead, afforded,52 53 in 90% yield, a 1 1 mixture of the (5R)- and (5S)-5,6-dideoxy-5-C-[(RS)-(eth-oxy)-phenylphosphinyl]-D-xyio-hexofuranoses (85), which was separated by thin-layer chromatography (t.l.c.). Similarly, (5RS)-5,6-di-deoxy-1,2 - O - isopropylidene- 5 -C- [(RS)-(methoxy)phenylphosphinyl]-... 

All of these examples illustrate the complexing ability of an ax-eq-ax sequence of oxygen atoms on a six-membered or of a cis-cis sequence on a five-membered ring. Attempts have been made to find other complexing sites on sugar molecules but with little success. The 0-3, 0-5, and 0-6 arrangement of hexofuranoses, which allows the ready formation of tri-dentate periodate (IS), and orthoformate esters (19), does not form stable complexes with metal ions. In solution the side-chain of 1,2-0-isopropylidene-a-D-glucofuranose (13) is in the extended zig-zag form... 

An analogous methyl 2,3-dideoxy-3-C-methylene-a-L-en/thro-hexopyranoside (20) was obtained10 from methyl 4,6-O-benzylidene-2-deoxy-a-L-eri/t/iro-hexopyranosid-3-ulose (19) it was used in the synthesis of olivomycose (see p. 242). There was also reported32,34 the preparation of 3-deoxy-l,2 5,6-di-0-isopropylidene-3-C-methyl-ene-a-D-rifco-hexofuranose (22) from 1,2 5,6-di-0-isopropylidene-a-D-nfeo-hexofuranos-3-ulose (21) in about 60% yield, followed by transformations into branched-chain sugar derivatives, including... 

Cyclohexan 2-Oxo-l,l,3,3-tetrakis-[hydroxymethyl]- VII/2b, 1462 6-Deoxy-a-D-galactopyranosid Methyl-3,4-O-isopropyliden-E19a, 153 (6-1 -> H) 5-Deoxy-a-D-xylo-hexofuranose ... 

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. ... 

Deoxy-6-thio-D-a yfo-hexose forms a 1,6-anhydro compound analogous to 270. S-Acetyl-5-deoxy-l,2-0-isopropylidene-6-thio-a-D-xyZo-hexofuranose is obtained either by nucleophilic displacement on the corresponding 6-p-tolylsulfonyloxy compound with potassium thioacetate or by the photochemical addition of thioacetic acid to... 

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. 

Oxidations of hexofuranose derivatives have been performed over Adams platinum catalyst, and a protective effect of a primary p-tolylsulfonyloxy group against oxidation at an adjacent C-5 hydroxyl group has been demonstrated. 3-Deoxy-l,2-0-isopropylidene-6-0-p-... 

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-... 

O-isopropylidene-a-D-xylo-hexofuranose and 6-deoxy-l, 2-O-iso-propylidene-)8-L-idofuranose in 62 and 30% yield, respectively. Various conditions were tested, " without success, for raising the yield of 5-deoxy-l,2-0-isopropylidene-a-D-xt/io-hexofuranose the yield was significantly lowered (about 30%) when the hydride reduction was performed in tetrahydrofuran. A mechanism was proposed for formation of the two products namely, that formation of 6-deoxy-... 

Hexofuranose, 3,6-anhydro-5-deoxy-l,2-O-isopropylidene-a-D-xylo-, 241 —, 5 - deoxy -1,2 - O - isopropylidene - a - D -xylo-, 275... 

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