Pyranoid compounds

2 Pyranoid Compounds. - 3.2.1 Compounds with Short-chain 

Reagents i, BuaSnH, AiBn ii, H2O2, NaHCOs, MeOH, H2O 

Free radicals derived from 0-acetylated glycosyl bromides with nickel catalysis add to acrylates and acrylonitrile to give C-glycosides with axial C-1 substituents as expected.  

A sulfoxide derived from phenyl 3,4-0-isopropylidene-l-thio-P-L-fucoside, on treatment with MeLi followed by fcrt-BuLi, gave the glycosyl carbanion which added to iso-butanal to give p-C-glycosides as an epimeric pair, and the a-thioglycoside led to the a-C-glycosides.  

Compound 130, made by oxidative cleavage of the GlcNAc allyl C-glycoside followed by Wittig extension, has been used to make the nucleoside derivative 131 for studies of potential inhibitors of chitin synthases.  

1 Pyranoid Compounds.- The main routes to these compounds depend upon nucleophilic attacks at the anomeric centres of a wide range 

D-glucoslde derivative, treated with trlmethylsilylated enol ethers or with aromatic hydrocarbons, gave a-linked products with C -bonded 

Anhydro-sugar derivatives can also be used to produce C-glycosldes, the corresponding 1,2- and 1,6-anhydrldes having been 

Free sugars themselves can undergo nucleophilic attack at the anomeric centre as in the synthesis of the ester (42) from the corresponding free sugar by means of a Wittig reagent,and related procedures must have been involved in the generation of compounds such as (43),and (45) by reactions of 

Complex ketose derivatives can be formed by carbanion attack at the carbonyl group of aldonolactones, deoxygenation at the anomeric centre thus giving C-glycosidic products. In this way the isomeric alkenes (46) and (4 ) were made by use of an acetylinic nucleophile 

6- tri-0-benzyl-2-deoxy-a-D-galactopyranosyl pyridylsulfone, on treatment with samarium diiodide and cyclohexanone, gave the 1-hydroxycyclohexyl C-glycosides with the ot/p ratio 10 1. Other carbonyl compounds reacted similarly, and much poorer ot/p selectivity was observed when the P-linked sulfones were used.  

Photocyclisation of the 2,3-unsaturated a-C-glycoside having a 3-oxo-2-methyl-but-l-yl aglycon afforded the mixed isomers 79 to offer a new way of making functionalized cyclopentanes. In related work, 5e-phenyl 2-allylamino- 

6- tri-0-benzyl-2-deoxy-l-selenyl-D-glucopyranoside, on treatment with tributyltin hydride/triethylboron in a stereoselective process, afforded the bicyclic 

treated with butyllithium followed by sodium methoxide, underwent 1,2-Wittig rearrangement to give the isomeric dialkyne 82. Likewise the isomer of the starting material with inverted stereochemistry at C-1 gave the anomerically 

Reagents i, CFaTms, Bu4NPh3SnF2 (cat.) li, tri-O-acetyl-D-glucal, BFa-EtjO 

Reaction of tri-O-acetyl-D-glucal with phenyl alkyl ethers in the presence of tin(IV) chloride gave predominantly 2,3-unsaturated glycosides linked through 

Reagents i, DIBAL ii, POCI3. Py iii, BH3 iv, HaOj, NaOH v, ZnCb, Et20 

C-Glycosidically linked disaccharides have now become of considerable importance and a review has covered the preparation of such compounds as well 

Reagents i, Li—=— Tms ii, AC2O, Py iii, TmsO, SnCU iv, C2H2, CIRh(PPh3)3 

Reagents i, BuaSnH, AIBN ii, m- CPBA iii, AC2O, NaOAc 

An extensive range of methods involving anomerlc substitution reactions have been applied, several utilising glycosyl lithium Intermediates, and Sinay and his coworkers have described fully 

Such nucleophilic intermediates take part in conjugate addition 

Other methods have depended upon nucleophilic attack at the anomerlc centre these include reaction of tetra-O -acetyl-a-D-gluco-pyranosyl chloride with lithium diaryl cuprates to give 6-C - 

An Improved procedure for making both pyranosyl and furanosyl 

Suitably protected phenylthio glycosides treated with dialkyl zincs in di-iodomethane offer a new route to -glycosides. Both a- and 3-D-glucopyranose compounds gave products with a 3 1 a g 

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However, there still remain a number of characteristic features (not yet mentioned) which differentiate the mass spectra of furanoid from those of pyranoid compounds. For example, the mass spectrum of methyl tri-O-methyl-a,/S-L-arabinofuranoside (see Fig. 2) contains no D and no Bt ions, their formation being structurally impossible. The peak at m/e 88 is of low intensity, as the formation of both of the m/e 88 fragments (Hf and H ) proceeds concomitantly with the formation of unfavored carbenes ... 

That bromine atoms can be introduced directly at C-5 of some pyranoid compounds, at C-4 of some furanoid derivatives, and at chemically related centers of certain other monosaccharide compounds was discovered following the finding by Dr. Richard Fumeaux, during his Ph.D. studies in Wellington, that phenyl tetra-O-acetyl-1 -thio-/i-D-glucopyranoside (1) is con-... 

Lichtenthaler and his coworkers, recognizing that pyranoid compounds bearing carbonyl groups at C-2 or C-4 would be subject to captodatively... 

The many carbohydrate compounds to have been examined (see Section II) clearly raise the interesting question of the combined effects of the ring-oxygen atoms and of the other substituents on radicals formed at C-l and at C-4 and C-5 for furanoid and pyranoid compounds, respectively. The several acetylated / -D-glucopyranosyl derivatives (100) to have been studied are particularly suitable compounds for examination in this regard, since, because of their near-symmetry, the effects of the anomeric substituent (X) in respect of its ability to facilitate photobromination at C-l can be compared closely with the effect of the substituent (CH2OAc) at C-5. 

Pyranoid compounds such as 252 undergo hydroboration and hydrogenation to give mixtures of D-glucose and L-idose derivatives and their 6-deoxy analogues, respectively, the ratios depending on reaction conditions and on structural details of the substrates. Acid-catalyzed hydrolysis leads to 6-deoxyaldos-5-uloses.6... 

The physical properties and many chemical properties of monosaccharides depend on the molecular shape. Equilibria of pyranoid compounds depend largely upon the axial-equatorial relationship between substituents on the rings. Thus, the alp ratio of pyranoses is governed to some extent by the tendency of the anomeric hydroxyl group to occupy the less hindered equatorial substituent orientation. 

Two other apphcations of the W-acetyl inversion in pyranoid compounds... 

These pyranoid compounds offer a means of obtaining 1-deoxy-ketoses (seep. 259), and continue to provide a source ofaldos-5-uloses the sugar component of hygromycin A has thus been prepared by hydrolyzing methyl 6-deoxy-a-D-arafcino-hex-5-enopyranoside.149 In related fashion, methyl 6-deoxy-2,3-0-isopropylidene-a-D-Zyxo-hex-5-enopyranoside (81) was isomerized150 in the presence of an acid to methyl 6-deoxy-2,3-0-isopropylidene-a-D-Zyxo-hexosid-5-ulose (82). 

With the pentoses and 6-deoxyhexoses, from which pyranoid compounds analogous to (149) cannot be formed, both the saturated, and unsaturated, acyclic products have been isolated from reaction mixtures. For example, L-rhamnose, affords, on oxidation with peroxypropionic acid in aqueous dioxane, the crystalline, simple sulfone and unsaturated... 

In all of these instances, a simple oxidation occurs, and, depending on the conditions, the products may suffer a 3-elimination to give the unsaturated sulfones hence, for the hexoses, the pyranoid compounds formed by nucleophilic addition of 0-6 at C-2 are obtained. 

Few examples existing in the literature support the validity of the rule of Brown and coworkers, in these four types of enolacetal sugars. The 4,5-unsaturated 4-deoxyhexopyranuronates having different substituents have proved to be stable compounds that can be stored for several years at room temperature without undergoing decomposition. This behavior seems to differ from that of pyranoid compounds bearing an exocyclic, enolacetal double bond. 

These few examples seem to support the validity of the stability rule of Brown and coworkers for the group of pyranoid sugars having a single, enolacetal double bond that is, pyranoid compounds having an exocyclic, enolacetal double bond are more reactive (less stable) than... 

However, the similar acrylate system involved in a pyranoid ring proved to be highly stable, in contrast to pyranoid compounds bearing the parallel-oriented, dienol ether linkage, which proved to be unstable and which polymerized readily. 

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