Abnormal Reimer-Tiemann reaction

C-sulfonylmethylation, -Reimer-Tiemann reaction, abnormal 8, 843 Reissert compds. 

Ab initio and density functional calculations indicate that the first step of the abnormal Reimer-Tiemann reaction involves barrierless formation of an intermediate by nucleophilic attack on CCl2 of the /3-carbon of pyrrole anion. " This is followed by a single, concerted step to give the product, 3-chloropyridine. 

The abnormal Reimer-Tiemann reaction involves a ring expansion, in the classical case from a pyrrole to a 3-chloropyridine, resulting from an attack of dichlorocarbene on a double bond. An electrochemical equivalent can be made by electrolysis in a chloroform solution, where the electrogenerated base produces dichlorocarbene. By using this method, 2,3-dimethylindole could be transformed to 3-chloro-2,4-dimethylquinoline in fair yield some of the normal Reimer-Tiemann product, 3-dichloromethyl-2,3-dimethyl-3//-indole, was also formed [164]. 

Castiiio, R., Moiiner, V., Andres, J., Oiiva, M., Safont, V. S., Bohm, S. Theoreticai investigation of the abnormal Reimer-Tiemann reaction. 

The Reimer-Tiemann reaction, an aromatic substitution reaction that occurs under basic conditions, is in many respects a unique reaction. It is one of the few organic reactions whose industrial importance seems to increase yearly, notwithstanding the environmental hazards associated with the use of chloroform, while academic interest remains considerable. In addition to the fact that the normal reaction continues to intrigue chemists, the so-called abnormal Reimer-Tiemann reaction that furnishes substituted cyclohexadienes remains of considerable interest. Several previous surveys of the Reimer-Tiemann reaction have been published. Consequently, we focus here on recent developments. 

It is convenient to discuss the Reimer-Tiemann reaction in terms of its normal and abnormal versions. The normal reaction, discovered in 1876 by Reimer, consists of the treatment of a phenol or naphthol with chloroform in the presence of an alkali metal hydroxide solution (see equations 1 and 2), and results... 

It is interesting to compare early experimental work with the facilities available in a modem laboratory. Von Auwers was the first to separate the chloro ketones from the normal phenolic aldehydes of the Reimer-Tiemann reaction. Identirication and strocture proof by chemical means followed. It is a tribute to von Auwers skill and insight that his identification procedures have withstood the onslaught of modem spectroscopic means. Although the chloro ketones (equations 8-10) have been called the abnormal products of the reaction, in cases where the ortho and para positions are occupied (see equation 10) only ketonic material is obtained.In fact, the presence of the dichloro ketones provides one of the better arguments for the intermediacy of dichlorocarbene in the reaction mechanism. ... 

Although at first these ketonic by-products were mere curiosities, their potential value was noted by Woodward, who used the abnormal Reimer-Tiemann reaction for a synthesis of /ranr-10-methyldeca-lone from P-(ar)-tetralol (equation 11). This author applied this principle for the preparation of a 9-methyldecalone from an a-(ar)-tertralol (equation 12). ... 

As is the case with the normal reaction, the abnormal reaction can also be influenced by the use of 3-cyclodextrin to give higher selectivity for the para position. Australian chemists have carried out a careful product analysis of the normal, abnormal and ring-expansion products resulting from the Reimer-Tiemann reaction with a series of 4-alkylguaiacols. ... 

An abnormal Reimer-Tiemann reaction has been observed in which dichlorocarbene attack at the 2-position to the phenolic hydroxyl group was sterically blocked resulting instead in displacement of the methoxyl group at the adjoining position (ref.8). The hexahydrodibenzfuran depicted was obtained by the Diels-Alder reaction of 2-methoxybenzo-1,4-quinone and 1-methoxy-4(2-methoxyethyl)cyclohexa-1,3-diene followed by acidic rearrangement at ambient temperature. 

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