Acetate halogeno

Cyclic 1,3-diketones have been converted into / -halogeno-ketones (118) by tri-phenylphosphine dihalides in benzene or acetonitrile,100 although this paper adds little to previous work101 in this field. The reactions of phosphorus pentachloride with acetals have been extended to mixed acetals, such as (119).102 Only one product... 

Oxidation of sulphonamides in the presence of bromide or iodide ions and sodium methoxide in methanol also leads to formation of the N-halogeno intermediate. The nitrogen-halogen bond in these intermediates is weak and will undergo themiolysis. At -10 °C, reaction proceeds by base catalysed elimination of hydrogen halide and ftirther steps lead to an a-amino acetal 20. The reaction is carried out in an undivided cell and renders a-aminoacetals readily available for the iso-... 

All attempts to isolate 2-halogeno-l,3-dioxolanes or -1,3-dioxanes were unsuccessful. For instance, 2-chloro-l,3-dioxolane was detected only by photochlorination of 1,3-dioxolane (Ref. 118) at low temperature and 2-chloro-2-methyl-l,3-dioxolane was prepared by treatment of 2-methyl-l,3-dioxolane-2-carboxylic acid with phosphorus pentachloride at —60°, and shown119 to rearrange to 2-chloroethyl acetate on warming to 0°. For other examples of such problems, see especially, references 120 and 121. 

An earlier report51 that phenanthridone is brominated at C-2 on treatment with bromine in acetic acid has been confirmed291 chlorination (molecular chlorine) and iodination (iodine-iodate) in acetic acid give the corresponding 2-halogeno compounds in excellent yield.291 The bromination of 2-acetamidophenanthridone has also been described, although the orientation was not established with certainty.291... 

Note At least in simple cases, the Meissenheimer reaction appears to be unsatisfactory for the production of halogeno-l,8-haphthyridines. Thus 1,8-naphthyridine 1-oxide with phosphoryl chloride gave a difficult-to-separate mixture of 2-, 3-, and 4-chloro-l,8-naphthyridine (in ratio 36 7 57) 225 phosphoryl bromide and bromine/acetic acid both gave even worse mixtures... 

Replacement of the Halogen at Carbon Atom 1.—From the acetyl-dihalide derivative, the acetates of the 2-desoxy-2-halogeno-aldoses can be prepared by treatment with moist silver carbonate or oxide. 

Isomerization of yohimbine at position 3 is achieved by first dehydrogenation at positions 3,4 with V-halogeno compounds (6,7) or with mercuric acetate (7) and then reduction with zinc and acetic acid. The... 

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