Selective halogenation

The selective replacement of hydroxyl groups in carbohydrates by halogen has mainly been achieved by the use of (a) sulfuryl chloride, (b) reagents based on phosphorus compounds, and (c) reagents of the 

N-dimethyl(halomethaniminium) halide type. The subject of de-oxyhalogeno sugars has been discussed twice in this Series.345,346 

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SELECTIVE HALOGEN-LITHIUM EXCHANGE REACTIONS OF 2- 2 -HAL0PHENYL)ETHYL HALIDES ... 

Table 5.5 Variation in selected halogenated monoterpenes in Plocamium cartilagineum coUected from sites in Chile (from San-Martin and Rovirosa, 1986)...

The preparation of stannylthiazoles via ditin chemistry has not been widely utilized. In one case, the synthesis of 4-tributylstannylthiazole 43 started with selective halogen-metal exchange at C(2) by treating 2,4-dibromothiazole with n-BuLi [33]. Trapping the resulting 2-lithio-4-bromothiazole with propanal and subsequent Jones oxidation secured 4-bromothiazole 42. The Pd-catalyzed reaction of 42 with hexamethyldistannane in the presence of PdCWPhjP provided 4-tributylstannylthiazole 43. 

In triiodoimidazole 21, a selective Suzuki coupling was achieved at C(2), whereas a selective halogen-metal exchange in a diiodoimidazole 23 was realized at C(5). In addition, the Sonogashira reactions of haloimidazoles appear to be very substrate-dependent. 

Shikiya J, Tsou G, Kowalski J, et al. 1984. Ambient monitoring of selected halogenated hydrocarbons and in the California South Coast Air Basin. Proceedings of the 77th Annual Meeting of the Air Pollution Control Association, 1-21. 

Jafvert, C.T. and Wolfe, N.L. Degradation of selected halogenated ethanes in anoxic sediment-water systems. Environ. Toxicol C/je/n,.6(ll) 827-837. 1987. 

Then, selective halogenation has been carried out at mild conditions under which only the halogenation of the two primary hydroxyl groups occurs. The secondary hydroxyl groups remain intact under these conditions. The reaction proceeds smoothly with carbon tetrachloride and triphenylphosphine in anhydrous pyridine at 5°C for 18 hours (22). 1,6-Dichloro-1,6-dideoxy-3,4-0-isopropyli-... 

National Toxicology Program NTP Technical Report on Renal Toxicity Studies of Selected Halogenated Ethanes Administered by Gavage to F344/N Rats. Technical Report Series No. 45, NIH Pub No 96-3935, pp 1-52. Research Triangle Park, NC, US Department of Health and Human Services, 1996... 

Selective halogen-metal exchange at the 5-position has been achieved with 2,5-dibromo-4-chlorothiazole at -90°C in THF(Scheme 95), although the results obtained were very dependent upon the nature of the electrophile used [92JCS(PI)215]. 

In the application of emulsions for cleaning and polishing, a water phase and an oil phase (a selected halogenated solvent) are needed. The emulsions are used in cleaning and polishing the surfaces of metals and other hard surfaces (glass, etc.). 

Infante FI, Marlow PB. 1980. Evidence for the carcinogenicity of selected halogenated hydrocarbons included ethylene dichloride. Banbury Rep 5 287- 308. 

There is extensive literature on halogenocarbazoles prompted partly by searches for reagents and conditions whereby selective halogenations could be achieved. Reports vary probably because in some cases the major (or... 

The presence of bis[2-(A,A-dimethylamino)ethyl]ether allows a selective halogen-magnesium exchange of iodo- and bromoaromatics at ambient temperature using iso-propylmagnesium chloride. Sensitive carboxylic ester and cyano groups are well tolerated (equations 29 and 30). ... 

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