Halogenated Acetyl Groups

20 Aromatic Ketones Containing Only Acetyl Groups 

V CH — Preparation by reaction of paraformal- dehyde with 2,4-dihydroxy-5-dodecyl- 

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Regioselective deacylation has also been observed189 in the acid-catalyzed transesterification of some 3, 5 -di-0-acetyl-2 -deoxy-2 -halo-uridines in methanol to give the corresponding 3 -0-acetyl derivatives in yields of 36-66%. The presence of the 2-halogen substituent seems essential for the selectivity in the case of 2, 3, 5 -tri-0-acetyl-uridine, no significant differences in the reaction rates of the acetyl groups towards transesterification were apparent. 

DDT p,p -dichloro-diphenyl-trichloroethane. deacetylation removal of acetyl group, dealkylation removal of alkyl group, deaminate removal of amine group, dechlorination removal of chlorine group, de-ethylation removal of ethyl group, dehalogenation removal of halogen atom(s). 

Numerous derivatives of (1) have been thus prepared, notably 2,3-dimethyl (or dialkyl)benzofurans Bz-substituted by alkyl radicals,36,213-218 methoxyl groups,101,219-221 halogen atoms,217,222-224 aryl groups,225 acetyl groups,215,218,226 formyl groups,222,226 and carboxyl groups.226,227 The method is especially valuable in the case of formyl derivatives, which are difficult to obtain otherwise. 

This mechanism also serves to explain why orthoester derivatives are often formed when the acetyl group on carbon 2 is Irans to the halogen on carbon atom one.78 Then the carbonyl of the acetyl group is in position to take part in the replacement of the halogen ... 

By this method an acetyl group is converted to carboxyl by substitution of halogen for the three hydrogen atoms followed by cleavage of the resulting trihaloketone. For preparative purposes, it is desirable that no similarly replaceable hydrogen atom be present in the R radical. 

In a small number of examples <1971CJC3299, 2004CRV5151>, 1,2-dithioles without halogen at C-4, such as 118, have been converted with diacetylacetylene into the resulting thials 119, which can be isolated, and then via a known dimerization-desulfurization process to functionalized trienic tetrathiafulvalenes 120 with four electron-withdrawing acetyl groups. 

Regarding the orthoester formation in the ketose series, any acetyl-ketosyl halide may give at least a 1,2-orthoester because the acetyl group at position 1 is always free to approach, from the opposite side, the halogen atom at position 2 in either modification of the halide. 

In 1904 Fischer found that the presence of a halogen acyl group in the molecule of an amino acid again allowed of the preparation of the acid chloride, z.e., when the amino group of the amino acid was rendered stable, and that this compound was formed by the action of phosphorus pentachloride in the presence of acetyl chloride. As before, this acid chloride could be combined with the esters of amino acids or of polypeptides, e.g.—... 

Thiophenium ylides. The reaction of dimethyl diazomalonate with thiophene with conventional copper catalysts is extremely slow, but does result in dimethyl thiophene-2-malonate (2) in about 35% yield. When rhodium(II) aceta is used as catalyst, the reaction at 20° is still slow (18 hours), but results in thiophenium bismethoxycarbonylmethylide (1) in 95% yield. This reaction is facilitated by halogen substituents the ylides are not formed from thiophenes substituted with cyano, formyl, or acetyl groups. ... 

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