Anhydro compounds reductive

Reduction of isoquinamine gave the dihydro derivative, allodihydro-isoquinamine (XVI) which, in acid, unlike model dihydropseudoindoxyls, ring closed to the anhydro compound (XV) rather than rearranging to the indole (19). This tendency to cyclize was also evidenced when isoquinamine was heated with acids, the quaternary salt being produced (16, 22). 

The same procedure was also applied to the synthesis of a-C-galactosyl compounds. Similarly, reductive ring opening of 1,2-anhydro sugar 93 with titanocene(m) chloride produces an anomeric radical 97 that can be trapped... 

The presence of a dichloromethylene group at the anomeric center of 82 facilitates proton abstraction at C-3 by a strong base (77), aifording the 4-deoxyglycos-3-ulose derivative 83. Reduction of the dichloromethylene group by Raney nickel gave a 1-C-methyl derivative with high stereospecificity, which opens the way to a series of 2,5-anhydro-l-deoxyalditols. Compound 83 was the key intermediate for the synthesis (78) of tosyl L-(+)-epi-muscarine (84a) and tosyl L-(+)muscarine (84b). 

Cleavage of the dithioacetal groups from the products, followed by reduction of the resultant carbonyl derivatives (46, 49, 52) with sodium borohydride leads,68 with the three compounds (45, 48, and 51), to 1,4-anhydro-L-ribitol (2,5-anhydro-D-ribitol) (47), 1,4-anhydro-L-xylitol (2,5-anhydro-D-xylitol) (50), and 1,4-anhydro-D-arabinitol (2,5-anhydro-D-lyxitol) (53), identified by comparison with their enantiomorphs, 1,4-anhydro-D-ribitol,69 1,4-anhydro-D-xylitol,70 and 1,4-anhydro-L-arabinitol. 71... 

The Mitsunobu conditions, applied without any carboxylic acid, were shown to provide anhydro (3, 4 -epoxide)284 286 and dianhydro sucrose derivatives.331 Some of these compounds were further transformed by reduction (leading to dehydrosucroses) or ring-opening leading to sucrose epimers and dehydrohalo-or amino sucroses (see also Scheme 7).332... 

A key compound for levoglucosan chemistry is 1,6-anhydro-2,4-di-<3-tosyl-/ -D-gl ucopyranose (36)176 which, after treatment with sodium ethoxide, affords a valuable starting compound, l,6 3,4-dianhydro-2-O-tosyl-jS-D-galactopyranose, as a single product (see Section IV. 1). Another example illustrating synthetic versatility of the ditosylate 36 is its oxidation to 3-keto derivative 37124.210.211 followed by reductive detosylation to afford the useful chiral synthon, l,6-anhydro-2,4-dideoxy-/i-D-g/ycero-hcxopyranos-3-ulose (38).210,212 Keto derivative 37 is readily isomerized by the action of pyridine into compounds of the D-arabino, D-xylo, and D-lyxo configurations.210... 

Nevertheless, compound 81 was definitely obtained later by deamination of 2-amino-l,6-anhydro-2-deoxy-j6-D-mannopyranose (103) with nitrous acid, and was identified by reduction to 2,5-anhydro-D-glucitol.366 An analogous deamination was performed with 2-amino-l,6-anhydro-2-deoxy-3-0-tosyl-/l-D-altropyranose to give, after detosylation, 2,5-anhydro-D-allose.361... 

In the case of 1,6 2,3- (136) and l,6 3,4-dianhydro-/I-D-talopyranoses, the diaxial opening of the oxirane ring prevails, but a trend to diequatorial opening496 498 is apparent with l,6 2,3-dianhydro-4-deoxy- and 1,6 3,4-dianhydro-2-deoxy-/l-D-/yxo-hexopyranoses.169,432,493 Using 1,6 2,3- and l,6 3,4-dianhydrohexopyranoses as starting compounds allowed the preparation of a complete series of 12 isomeric 1,6-anhydro-monodeoxy-/Fn-hexopyranoses and 6 corresponding 1,6-anhydro-dideoxyhexoses,499 mainly by catalytic or complex hydride reductions.462,500... 

When 3,4-di-O-acetyl-D-xylal (5), prepared by a modification of the procedure of Helferich and coworkers, was allowed to react with a mixture of carbon monoxide and hydrogen at a pressure of about 4000 Ib./in. and at a temperature of about 130° for about 90 minutes, in the presence of preformed dicobalt octacarbonyl in benzene as the catalyst, a mixture of two inseparable, partially acetylated hexitols was obtained in over 90% yield. Deacetylation of the latter with sodium methoxide in methanol yielded, in almost equimolar proportions, the chromatographically separable hexitols, l,5-anhydro-4-deoxy-L- yio-hexitol (6) and l,5-anhydro-4-deoxy-D-arahino-hexitol (7). Whenever the mixture of products was contaminated by the precursor aldehydo compounds, a prior reduction of these with sodium borohydride greatly facilitated the isolation of (6) and (7) in pure form. 

The stereochemistry at C-5 of each of the hexitols (6) and (7) was determined in the following way. Periodate oxidation of these hexitols afiForded dialdehydes (8) and (9), which, on subsequent reduction with sodium borohydride, afforded the enantiomeric trihydroxy ethers (10) and (11). The configuration at C-3 of the ether (10) was then correlated with that of C-4 of the known l,4-anhydro-5-deoxy-D-arabino-hexitol (12), as follows. Periodate oxidation of (12), followed by reduction of the resulting dialdehyde with sodium borohydride, yielded a trihydroxy ether that was identical with (10). If it is assumed that no inversion of configuration at C-3 or C-4 of 3,4-di-O-acetyl-D-xylal occurs during the oxo reaction, then compounds (6) and (7) are l,3-anhydro-4-deoxy-L-JC /lo-hexitol and l,5-anhydro-4-deoxy-D-arobino-hexitol, respectively. 

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