29419-97-4

The work reveals that a chelate-Type interaction in the transition state of a β-Aminoalkyl radical in a copper(i)-catalyzed 5-exo-Trig radical cyclization step changes the usual stereochemistry of the NH-pyrrolidine ring predicted by the Beckwith-Houk transition state model. In contrast, the rigidity in the fused β-Aminoalkyl radical changes the Baldwin's predicted 5-exo to 6-endo cyclization mode, preferentially forming a piperidine ring over a pyrrolidine ring via a geometrically constrained transition state. The resultant diverse NH-pyrrolidines, pyrrolines and piperidines are sources of the bioactive natural product roseophilin and the drug Ritalin among others.

The invention provides a method for the preparation of an intermediate for use in synthesizing a lower alkyl phenidate compound of formula (I), wherein each R1 independently represents an optionally substituted aryl, heteroaryl, alkyl, cycloalkyl, alkoxy, aryloxy, acyl, carboxyl, hydroxyl, halogen, amino, nitro, sulfo or sulfhydryl group, R2 represents a hydrogen atom or a lower alkyl group, n represents an integer from 1 to 5 and m represents an integer from 1 to 3 or a pharmaceutically acceptable salt thereof; which method comprises the steps of: (a) flowing a tosylhydrazone compound of formula (IV), wherein R1, n and m are as defined above in relation to the methylphenidate of formula (I), an organic base and an organic solvent into a fluidic network; and (b) reacting the tosylhydrazone compound of formula (IV) and the base in the fluidic network under thermal and/or photochemical conditions to form a transient diazoamide compound of formula (V), wherein R1, n and m are as defined above in relation to the methylphenidate of formula (I).

The present invention is directed to an improved process for the preparation of methylphenidate, stereoisomer, mixture of stereoisomers and pharmaceutically acceptable salts thereof, more particularly, the sulfate and hydrochloride salts of methylphenidate, di-threo-methylphenidate and dex-methylphenidate. Methods of removing or reducing the amount of impurities from the above described process are also disclosed.

The present invention describes a process for the preparation of methylphenidate hydrochloride. The process involves the esterification of ritalinic acid and methanol in the presence of an acid catalyst at a low temperature. The process may optionally involve the addition of an orthoester.

Disclosed herein is a process for the preparation of methyl phenidate hydrochloride (Formula I), comprising the steps of; hydrolyzing α-phenyl-α-pipyridyl acetamide (Formula II) in presence of mineral acid at reflux temperature and subsequent neutralization to yield threo -α-phenyl-α-pipyridyl-2-acetic acid (Formula III) which in presence of acidic catalyst reacts with methanol followed by treatment with alcoholic hydrochloride solution produces methyl phenidate hydrochloride.

A synthetic process for the preparation of amino acid esters such as methylphenidate and analogs thereof is disclosed. The process involves reacting an amino acid such as α-phenyl-α-(2-piperidinyl)acetic acid or an analog thereof with an alcohol such as methanol in the presence of an acid and a water sequestrant such as trimethyl orthoacetate. In some embodiments, the water sequestrant is added to the reaction mixture after an initial period of esterification and then the reaction is allowed to continue. The α-phenyl-α-(2-piperidinyl)acetic acid methyl ester or analog thereof is then isolated from the reaction mixture. In one variation of the process, the supernatant liquid may be recycled in subsequent runs to increase yield and product purity.

A method to resolve the stereoisomers of an optically active compound comprising an amine moiety. The method provides a mixture comprising two stereoisomers of a compound comprising a amine moiety. The method supplies l-fenchyloxyacetic acid, treats the mixture of stereoisomers with that l-fenchyloxyacetic acid, and collects one of those two stereoisomers having greater than a 99 percent enantiomeric excess.

The present invention provides a process for the preparation of threo-methylphenidate hydrochloride. According to a preferred embodiment, the process comprises the following steps: (a) contacting 1-(phenylglyoxylyl)piperidine arenesulfonylhydrazone of the formula wherein Ar denotes an aryl group, where the aryl group may be substituted by a C1-C6 alkyl, halo or nitro group; with an inorganic base in the presence of a water immiscible organic solvent and a phase transfer catalyst to obtain (R*,R*)-enriched 7-phenyl-1-azabicyclo[4.2.0]octan-8-one of the formula: (b) reacting the (R*,R*)-enriched 7-phenyl-1-azabicyclo[4.2.0]octan-8-one prepared in step (a) with a solution of hydrogen chloride in methanol to obtain threo-enriched methylphenidate hydrochloride; (c) crystallizing the threo-enriched methylphenidate hydrochloride prepared in step (b) to give the desired threo-methylphenidate hydrochloride. Preferably, the threo-methylphenidate hydrochloride produced by the process of the present invention contains no more than 1% of the erythro-isomer.

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