Halocarbonyl group

The intramolecular cyclization of 2-(3,4-dimethoxybenzyl)-3-(N-ben-zyl-4-piperidinyl)propionic acid 1 followed by treatment with HC1 [18] as shown in Scheme 3.6. Cyclization of compound 1 was carried out under Friedel-Crafts reaction conditions, optionally with previous derivatization of the carboxylic group to a halocarbonyl group. Preferably, the cyclization process was carried out in the presence of protic acids or Lewis acids or a mixture of protic and Lewis acids gives donepezil 2 which is converted to the hydrochloride salt 3. 

The reaction of a thioamide with a-halocarbonyl compounds has been applied extensively, and many thiazoles (10) with alkyl, aryl, aralkyl, or heteroaryl functional groups at the three 2-, 4-, or 5-positions have been reported (Scheme 6). 

Two classes of promoter have been identified for iridium catalysed carbonylation (i) transition metal carbonyls or halocarbonyls (ri) simple group 12 and 13 iodides. Increased rates of catalysis are achieved on addition of 1-10 mole equivalents (per Ir) of the promoter. An example from each class was chosen for spectroscopic study. An Inis promoter provides a relatively simple system since the main group metal does not tend to form carbonyl complexes which can interfere with the observation of iridium species by IR. In situ HP IR studies showed that an indium promoter (Inl3 Ir = 2 1) did not greatly affect the iridium speciation, with [MeIr(CO)2l3] being converted into [Ir(CO)2l4] as the batch reaction progressed, as in the absence of promoter. 

Olefinic azo compounds, in which the double bond is conjugated with the azo group, have been prepared from a-halocarbonyl compounds by reaction with a substituted hydrazine to form a hydrazone which, on treatment with a base, is dehydrohalogenated and isomerized to an olefinic azo compound. The reaction may be represented by Eqs. (19) and (20). 

The [M2(CO)8Cl3] anions are the first halocarbonyl complexes (without other ligands in the coordination sphere) of group VA metals to be reported. They probably originate from the unstable HM(CO)6 carbonyls. 

A number of reports of high nuclearity palladium clusters have been made in recent years. Palladium halocarbonyl clusters of unspecified nuclearity [PdX(CO)] (X = C1, Br) have been prepared by several groups of workers through the carbonylation of [PdCl2(MeCN)2] or PdX2 (X = Cl, Br).112-114 These decompose in solution to give Pdn and Pd°. When Na PdClJ was used as a precursor, then an anionic palladium(II) dimer (22) resulted.113... 

Reaction of an alkylborane with a-halocarbonyl compounds in the presence of a base leads to the replacement of the halogen atom in the carbonyl compound with an alkyl group from the borane. The reaction is most commonly applied to a-bromoesters (Equation B3.18). 

Five-membered N-heterocycles of general structure (128), carrying an a-XH grouping, react with a-halocarbonyl compounds to give quaternary salts (129) and (131) which readily undergo cyclodehydration to give (5,5)-fused pyrroles (130) and imidazoles (132). With (128 X = S) and a-halocarbonyl compounds, cationic-fused thiazoles (134) are obtained by treatment of the intermediates (133) with a strong acid (HA). 

This article is concerned with six- and seven-coordinate halocarbonyl complexes of molybdenum(II) and tungsten(II) (Section II), of which earlier reviews by Colton et al.2 on substituted halocarbonyls of group 6 transition metals and on steric effects in substituted halocarbonyls of molybdenum and tungsten3 have been published. Also, reviews on the structures of seven-coordinate compounds by Drew in 19774 and by Melnik and Sharrock in 1985s contain relevant material. 

Szymanska-Buzar et a/.230-234 have studied how Group 6 metal halocarbonyl intermediates are involved in the catalytic activity of these complexes in the presence of CC14230 231 and ZrCl4230-234 toward the transformation of both alkenes230-233 and alkynes.234... 

We can consider disconnection to this synthon to be a two-group disconnection because the a halocarbonyl equivalents are easily made by haioganation of a ketone, ester, or carboxylic acid (see Chapter 21) and the carbonyl group adjacent to the halide makes them extremely reactive electrophiles (Chapter 17). 

The range of suitable participants in the Michaelis-Becker reaction is essentially the same as for the Michaelis-Arbuzov reaction. Halo-aldehyde and -ketone substrates suffer the competing reaction of direct attack at the carbonyl group leading to Perkow reaction products (with a-halocarbonyl compounds) or Pudovik reaction products, which often cyclize (cf. Sections 4 and 6). 

Another common method for cleavage of substituents a to a carbonyl group involves reaction of the substituted carbonyl compound with an appropriate nucleophile. Such reactions are believed to occur by nucleophilic attack upon the a-substituent to afford an enolate (equation 2). Nucleophiles which can accomplish this conversion encompass a wide variety of structural types. Some of the best methods for reduction of halocarbonyl compounds fall into this category. 

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