Branched-chain derivatives

Ozonolysis and subsequent reduction open the way to formyl and hydroxymethyl branched-chain derivatives [18]. High stereoselectivities are generally observed on Grignard addition on conformationally biased ketosugars such as 3 (Scheme 6), equatorial attack being strongly favored, giving the axial alcohol 4 as the major product. 

An interesting reaction has been developed by Hanessian to reach the same type of branched-chain derivatives, without the need to prepare enones [62], The enol acetate 38 (Scheme 18), easily prepared by Ferrier rearrangement of 2-acetoxyglucal, underwent... 

Table III gives preparations of six-, seven-, and eight-carbon ketoses, and their methylated, deoxygenated, azido, amido, and branched-chain derivatives. All these are first obtained as ketose phosphates, but this is not a severe restriction, for, apparently, enzymic hydrolysis with phosphatases is always successful. Phosphatases constitute a versatile group of enzymes, easily...

Epoxy sugars are frequently used as starting compounds in the synthesis of sugar derivatives (compare Section IV) such as halo, amino, azido, thio, deoxy, and branched-chain derivatives. The oxirane ring is in general more reactive than the oxetane or oxolane ring. It is opened with nucleophiles under base or acid catalysis. On the other hand, the oxirane ring remains unattacked under the conditions of catalytic debenzylation on palladium,... 

The reactivity of the carbonyl group in a,/3-unsaturated dialdoses was studied in more detail. The interaction with phenylhydrazine and its derivatives led to different results. 3-0-Benzyl-l,2-0-cyclo-hexyl idene-5,6-dideoxy-a-D-xyZo-hept-5-e nodialdo-l,4-furanose (56) gave57 a (2,4-dinitrophenyl)hydrazone. Action of (2,4-dinitrophenyl)-hydrazine on derivatives 67 led18 to complex mixtures. In the case of the acetylated derivatives (66), as well as of branched-chain derivatives (69), the interaction with (2,4-dinitrophenyl)hydrazine resulted in the formation of the expected hydrazones (Refs. 24 and 51, respectively). The interaction with phenylhydrazine was, however, proved to proceed by two paths in this case. Only the nitro derivatives (66, R = p-nitrophenyl) and (69, R = p-nitrophenyl) were shown24,51 to form the expected hydrazones. The phenyl derivative 66 (D-galacto, R = Ph) and p-methoxyphenyl derivative 69 (R = p-MeOC8H4) afforded substituted pyrazolines (74) (Ref. 24) and (75) (Ref. 51), respectively, as a result of subsequent intramolecular addition of a... 

The branched-chain derivatives 97 and 98 were prepared51 from L-sorbose pentaacetate and 2,3 4,5-di-0-isopropylidene-aZdeht/do-L-arabinose, respectively. In the latter case, a branched-chain phos-phorane, namely methoxycarbonyl(methoxycarbonylmethyl) methyle-nephosphorane, was employed. 

The interaction of l,2-0-isopropylidene-a-L-g/t/cero-tetrofuranos-3-ulose and 5-deoxy-l,2-0-isopropylidene-/3-D-threo-pentofuranos-3-ulose with ylide 149 (R = H, X = SMe) leading to branched-chain derivatives (159a) and (159b), respectively, has also been reported.85... 

A number of more complex structures, useful in total syntheses, are accessible from olefins formed by Wittig olefinations of keto-sugars. A fmitful reaction is the dihydroxylation of double bonds. Obviously, methylene derivatives will give the hydroxymethyl branched-chain derivatives. 

Standard procedures have been used on laevoglucosenone to produce a series of unsaturated branched-chain derivatives (18), which were also reduced to the corresponding 3, 4-dldeoxy analogues. The assigned configuration was established by X-ray crystal analysis (R=0H). 

An example of highly stereoselective enderived ketone 12 with 2-(trimethylsiiyl)thiazole (2-TST), leading to the branched-chain derivative 13 (Figure 8). 

Yoshimura, j., K. Kobayashi, K. Sato, and M. Funabashi On the Configuration of Branched-Chain Derivatives of 1.2 5.6-Di-O-isopropylidene-a-D-r/ o-hexofuranose-3-ulose. Bull. Soc. Chem. Japan. 45, 1806 (1972). 

The use of trifluoro(fluoroxy)methane for the stereospecific introduction of a fluorine atom at the branching point of branch-chain sugars has been reported previously (see Vol. 9, p. 56). The fluorinated branched-chain derivative (403) has been converted into 3-C-acetoxymethyl-6-0-benzoyl-3-deoxy-3-fluoro-D-glucose,... 

The synthetic approach to 4 -(hydroxymethyl)ribonucleosides shown in Scheme 88 is based on aldol coupling of the nucleoside-5 -aldehyde (583) with formaldehyde and accompanying Cannizzaro reduction by the excess of formaldehyde. The 2, 3 -0-methylene derivative (584) was obtained as a by-product of the reaction. The branched-chain derivative (363) (see Chapter 13) also condensed with a variety of heterocyclic derivatives e.g. 6-chloropurine and JV -benzoyl-N ,9-bis(trimethylsilyl)adenine] to give, after deacetylation, 4 -(hydroxymethyl)ribo-nucleosides. -6-Chloro-9-(5,5-dimethylfuran-2-yl)purine (585) has been synthesized using the triol (586) derived from L-glutamic acid (see Scheme 65). ... 

The treatment of 4,6-0-benzylidene-3-deoxy-a-D-eryr/iro hexopyranosid-2-ulose and the corresponding 2-deoxy-3-ulose with carbon disulfide-methyl iodide and sodium hydride gives branched-chain derivatives 43 and 44 respectively. Reaction of 43 with ethanol in / -toluidine or p-anisidine gave, unexpectedly, derivatives 45 and 46. 

The reaction of crotyl ether 156 resulted in the predominant formation of (k)-configured C-butenyl derivative 158, thus demonstrating that sigmatrop-ic rearrangement in this system preferably proceeded through a chairlike transition state 157 (Scheme 30). The deoxy branched-chain derivatives obtained contain an array of functional groups suitable for selective further manipulations and thus appear to be attractive chiral building blocks for... 

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