Abnormal Reimer-Tiemann

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]. 

The total synthesis of the tricyclic sesquiterpene (+)-P-copaene was accomplished by E. Wenkert and co-workers. The required bicyclic starting material was prepared in three steps from carvacrol. In the first step, carvacrol was subjected to typical Reimer-Tiemann conditions. The abnormal Reimer-Tiemann product, 6-dichloromethyl-3-isopropyl-6-methyl-cyclohexa-2,4-dienone, was obtained, and upon treatment with sodium carbonate in DMSO, cyclization occurred to afford a bicyclic halo ketone. The double bonds were then hydrogenated in the presence of Pd(C) catalyst. 

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. 

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). ... 

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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