Other Halogenated Derivatives

Braunova, D. Stropova, and M. Cerny, CoU. Czech. Chem. Comm., 1977,42,120. 

Dichlorocarbene (generated in situ from chloroform) reacted with l,2 5,6-di-0-isopropylidene-a-D-glucofuranose in a phase-transfer system to give the rearranged product 6-chloro-6-deoxy-l,2 3,5-di-0-isopropylidene-a-D-glucofuranose, whereas 2,3 5,6-di-O-isopropylidene-a-D-mannofuranosyl chloride was obtained from the reaction of dichlorocarbene with 2,3 5,6-di-0-isopropylidene-a-D-manno-furanose. The a-D-mannofuranosyl chloride derivative was used to prepare the corresponding methyl and benzyl a-glycofuranosides and in the synthesis of a-linked disaccharide derivatives. 

4-Tri-O-acetylxylaryl dichloride reacted with diazomethane to give the expected bis(diazoketone) and a by-product having structure (146), which yielded the heptopyranulose derivative (147) on treatment with hydrogen bromide. A mixture of the 2,7-anhydro derivatives (148) and (149) was obtained when (147) reacted with sodium azide in acetone. 

Reagents i, MeOH-Ag COj ii, MeOH iii, BzCl-py iv, LiAlH v, Zn-AcOH 

Matsuura, T. Kunieda, and T. Takizawa, Chem. and Pharm. Bull. (Japan), 1977, 25, 239. 

Selective acid catalysed methanolysis of 2,3,2, 3 -tetra-0-benzyl-4,6 4, 6 -di-0-benzylidene-a,a-trehalose gave the monoacetal which was converted into the dimesylate and from this 6-deoxy-6-fluoro-a,a-trehalose was obtained. In the course of the work 4-chloro-4,6-dideoxy-6-fluoro-a-D-galactopyranosyl a-D-glucopyranoside was produced (as a derivative), and 6-iodo, 6,6 -di-iodo, 6-azido-, and 6,6 -diazido-trehalose compounds were also prepared. 6-Deoxy-6-fluoro- and 6-deoxy-6-iodo-trehalose were also obtained by way of the 

A very efficient method of introducing iodide (and presumably other nucleophiles) into carbohydrates involves the use of trifluoromethanesulphonate esters and their displacement with tetrabutylammonium iodide in refluxing benzene. Several monodeoxymonoiodo compounds were made in this way including compounds (17) and (18) which are difficult to obtain by more usual methods.  

5 -Bromo-, chloro-, and iodo-derivatives of showdomycin are referred to in Chapter 18 

The characterization of megosamine, a constituent of megamycin, as 2,3,6-trideoxy-3-dimethylamino-L-r/feo-hexopyranose, and not the corresponding D-lyxo C-5 epimer D-rhodosamine previously claimed, is referred to in Chapter 18. 

7-Acetamido-6,7,8-trideoxy-l,2 3,4-di-0-isopropylidene-a-D- and -L-gly-cero-D-galacto-octapyianoses have been prepared from D-galactose via the unsaturated nitro-sugar (9) by standard reactions.  

Pedersen, and P. Rasmussen, Acta Chem. Scand. (R), 1975,29, 389. 

Reagents i, BnCI-KOH ii, MeOH-H+ lii, PhsP-CCU iv, Pd-C-Hj v, Ac20-Na0Ac vi, AcjO-HjSO, vii, HBr-CHjCla viii, A -acetyl-bis(trimethylsilyl)cytosine ix, NHj-MeOH 

Chapter 4. Other chlorinated derivatives of sucrose have been prepared by treatment of partially esterified derivatives of sucrose with methanesulphonyl chloride-DMF. Thus, sucrose 2,3,3, 4, 6-penta-acetate reacted with this reagent at 85 °C to give a mixture of products from which the r,4,6 -trichloride (112), the l -0-formyl-4,6 -dichloride (113), the 4,6 -dichloride (114), and the 

The reaction of methyl 2,3-anhydro-j3-D-ribofuranoside with hydrogen bromide in acetic acid-acetic anhydride led to the formation of methyl 2,3-di-0-acetyl-5-bromo-5-deoxy-ajS-D-xylofuranoside, presumably via the intermediacy of the 3,5-acetoxonium ion. Similar treatment of methyl 2,3-anhydro-5-0-benzoyl-)8-D-ribofuranoside furnished methyl 2-0-acetyl-3-0-benzoyl-5-bromo-5-deoxy-ajS-D-xylofuranosides. 

Improved yields of methyl 2,3,4-tri-0-acetyl-6-deoxy-6-iodo-a-D-glucopyrano-side have been recorded in a synthesis that involved heating the corresponding 6-toluene-p-sulphonate with sodium iodide in butanone. Moffatt s group 

von Janta-Lipinski, G. Kowollik, K. Gaertner, and P. Langen, Nucleic Acids Res., Spec. Publ., 1975, 1 (3rd Symp. Chem. Nucleic Acids Components, 1975, S 45). 

The thermal degradation of derivatives of 6-chloro-6-deoxy-D-glucopyranose (e.g. methyl or phenyl 6-chloro-6-deoxy-o - and -jS-D-glucopyranosides) proceeded more readily than that of the parent sugars, since the hydrogen chloride liberated catalysed additional degradation.  

3-0-Benzyl-I,2-0-isopropylidene-6-0-toluene-/ -suIphonyl-a-D-glucofuranose reacted with sulphury chloride to give the 5-chloro-5-deoxy-jS-L-idofuranose derivative, which could be converted into (97) with sodium azide in DMF, or (98) with sodium iodide in acetone, or (99) with sodium methoxide. An 

Acetonation of 6,6 -dichloro-6,6 -dideoxysucrose with 2,2-dimethoxypropane, DMF, and toluene-p-sulphonic acid gave the l, 2 3,4-di- and the r,2-mono-acetals, which were isolated following acetylation. Similar treatment of methyl 6-chloro-6-deoxy-a-D-glucopyranoside gave the corresponding 2,3- and 3,4-acetal derivatives in yields of 28% and 9%, respectively. 

The acid-catalysed hydrolysis of methyl chlorodeoxyglycopyranosides is referred to in Chapter 3, and other references to chlorodeoxy-sugars occur in Chapters 6, 16, and 21. 

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Dihydroquinazolines are normally stable compounds but they deteriorate on long standing. Some examples are known to oxidize to the corresponding 4(3H)quinazolinones. 3-Methyl-3,4-dihydroquin-azoline is converted to the 4-oxo compound after three recrystallizations from light petroleum. The most remarkable example is 3,4-dihydro-6-fluoro-3(p-fluorophenyl)quinazoline [(44), R = F] which oxidizes at its melting point (137°-I38°C), Other halogenated derivatives of (44) are more stable. ... 

Fluorinated pyrimidines hydrolyze more readily than the other halogen derivatives and thus 5-trifluoromethyluracil 169 was able to be obtained from 2,6-difluoro-5-trifluoromethylpyrimidine 168 simply by heating with potassium fluoride in water at 50 °C <1996JFC(77)93>. 

The fluorines in fluorinated C60 can be displaced by a variety of nucleophiles. Furthermore, fluorinated C60 derivatives are likely to be synthetically useful because they are both more reactive, and more soluble than other halogenated derivatives (Taylor et al. 19925). They thus react readily with water, which negates their use as lubricants (Taylor et al. 1992 a). Mass spectrometry indicates that the products contain numerous hydroxy groups and epoxide links (probably from elimination of either HF or H20 from adjacent groups). An addition-elimination mechanism is probably involved since the normal SN2 process is ruled out because backside attack (Taylor et al. 19926) is impossible. 

V. Tyrosine Metabolism via Thyroid Hormones and Other Halogenated Derivatives... 

Steric aspects The fluorine atom is considerably smaller than the rest of the halogen atoms. Seen from the steric point of view it resembles more hydrogen than chlorine (Table 15.17). Effectively fluoro-derivatives differ from the other halogenated derivatives because fluorine forms with carbon particularly stable bonds and, in contrast to other halogens, is only rarely ionized or displaced. Because it is both chemically inert and of small size organic fluorine is often compared to hydrogen. 

Bromo-and chloro- derivatives of 2-pyridylazo reagents are more sensitive. The 5-Br-PADAP method has already been described. Other halogen-derivatives used in determining cobalt are 2-(5-chloro-2-pyridylazo)-5-diethylaminophenol (5-Cl-PADAP, formula 18.4) (e = 1.06-10 ) [43], 2-(5-bromo-2-pyridylazo)-l,5-diaminobenzene (5-Br-PADAB) (formula 18.5) (e = 1.16-10 ) [44,45], 2-(3,5-dichloro-2-pyridylazo-5-dimethylaminophenol) (e = 8.4-10" ) [46], and 2-(3,5-dibromo-2-pyrldylazo)-5-dimethylaminobenzoic acid (e = 1.55-10 at 673 nm) [47]. 

Carbon-Halogen Bonds. Carbon-halogen bonds may be prepared directly via the lithio intermediate or a second intermediate prepared from the lithio intermediate. For example, reaction of hexachloroethane with 2-lithiodimethylaminomethylferrocene gave the chloro derivative (Reaction 16) (23). However, preparation of other halogen derivatives via lithio intermediates has not been successful. A better and more versatile method for preparing the chloro, bromo, and iodo derivatives involves isolating a boronic acid intermediate as in Reaction 17 (24). 

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