Alkylation of phenothiazines

The parent drug of this series, promazine (24), was prepared originally as an antihistamine. Following the identification of the more potent chloro analog as an antipsychotic, it too came into use for that indication. The drug is prepared by straightforward alkylation of phenothiazine with w-C3-chloropropyl)di-methylamine by means of sodium hydride in xylene. ... 

Alkylation of phenothiazine with l-chloro-2-methyl-3-bromopropane affords the methylated analog (80) of the intermediate above. Use of this halide to alkylate the piperazine... 

Promazine Promazine, 10-(3-dimethylaminopropyl)phenothiazine (6.1.1), is prepared by the alkylation of phenothiazine with 3-dimethylaminopropylchloride in the presence of sodium amide [1-3]. 

Ethopropazine Ethopropazine, 10-(2-diethylaminopropyl) phenothiazine (10.2.7), is synthesized by alkylation of phenothiazine using l-diethylamino-2-propylchloride in the presence of sodium amide [39,40]. 

Sulfuration of the methoxy analog of 30 similarly gives a mixture of the desired 2-substituted phenothiazine (35) and byproduct (36). Alkylation of 35 as above affords methoxypromazine (37)... 

The most complex side chain of the piperazine phenothiazines is to be found on chlorimpiphenine (86). The side chain is prepared by first alkylating monocarbethoxypiperazine with the chlorobenzimidazole 83 [itself attainable by alkylation of methylbenzimidazole with a dihalide). Removal of the carbethoxy group affords the substituted piperazine, 85. Alkylation of this base with the chloropropyl phenothiazine, 58, affords finally the desired compound (86). ... 

Replacement of the terminal nitrogen of the piperazine by carbon is said to enhance the antiemetic activity of the phenothiazines at the expense of the other pharmacologic effects. The simplest compound in this series, pipamazine (88), is prepared by alkylation of nipecotamide (87) with the chloropropyl phenothiazine (58). Preparation of the analogous sulfoxide begins with acetylation of the thiomethyl compound, 89 [prepared by a route... 

The phenothiazine duoperone (5) combines structural elements found in phenothiazine and buty-rophenone antipsychotic agents. Alkylation of substituted piperidine 1 with 3-chloropropanol affords the intermediate 2 treatment of this with thionyl chloride converts the terminal hydroxyl to chloride. Alkylation of the phenothiazine 4 with halide 3 affords the antipsychotic agent duoperone (5) [1]. 

Attachment of the basic side chain to the phenothiazine nucleus by means of a carbonyl function apparently abolishes the usual CNS or antihistamine effects shown by most compounds in this class. The product azaclorzine instead is described as an anti anginal agent. Reduction of proline derivative 106 with lithium aluminum hydride gives the corresponding fused piperazine 107. Use of that base to alkylate the chloroamide 109, obtained from acylation of phenothiazine with 3-chloropropionyl chloride, leads to azaclorzine (110). ... 

Chlorpromazine Chlorpromazine, 2-chloro-10-(3-dimethylaminopropyl)phenothiazine (6.1.2), is synthesized in an analogous manner, except by alkylation of 2-chlorophenoth-iazine with 3-dimethylaminopropylchloride [4-6]. 

Prochlorpherazine Prochlorpherazine, 2-chloro-10-[3-(4-methyl-1-piperazinyl) propyl]-phenothiazine (6.1.4), is synthesized by the alkylation of 2-chloromethylphenthizine using 4-methyl-l-piperazinyl)propyl-3-chloride in the presence of sodium amide, or alkylation of 2-chloro-10-[(3-chloropropyl)]phenothyazine using 1-methylpiperazine [13-16]. 

The nitrogen of phenothiazine 16 can be deprotonated and alkylated, for example, with a palladium catalyst <1985AXC1804>. When an excess of butyllithium was used for 188, an additional halogen-metal exchange occurred and the compound could be doubly silylated (Scheme 14) <20020L623>. 

An alternate and more controlled approach to the synthesis of phenothiazines involves sequential aromatic nucleophilic displacement reactions. This alternate scheme avoids the formation of the isomeric products that are sometimes observed to form from the sulfuration reaction when using substituted aryl rings. The first step in this sequence consists of the displacement of the activated chlorine in nitrobenzene (30-1) by the salt from orf/io-bromothiophenol (30-2) to give the thioether (30-3). The nitro group is then reduced to form aniline (30-4). Heating that compound in a solvent such as DMF leads to the internal displacement of bromine by amino nitrogen and the formation of the chlorophenothiazine (30-4). Alkylation of the anion from that intermediate with 3-chloro-l-dimethylaminopropane affords chlorpromazine (30-5) [31]. 

The reduced basicity of phenothiazine nitrogen requires that even acylation proceed via the anion. The amide (34-2) from the methyl thioether (34-1) can be prepared, for example, by sequential reaction with sodium amide and acetic anhydride. Oxidation of that intermediate with peracid proceeds preferentially on the more electron-rich alkyl thioether to give the sulfone this affords the phenothiazine (34-3) on hydrolysis of the amide. Complex side chains are most conveniently incorporated in a stepwise fashion. The first step in the present sequence involves reaction of (34-3) as its anion with l-bromo-3-chloropropane to give (34-4). The use of that halide with alkylate piperidine-4-carboxamide (34-5) affords the antipsychotic agent metopimazine (34-6) [35]. 

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