Reimer-Tiemann conditions

There are a few scattered references to the reaction of nonphenohc six-membered heterocyclics with dichlorocarbene under Reimer-Tiemann conditions. Thus a mixture of 2-methylpyridine, chloroform, and sodium hydroxide is reported to contain sorbic acid and cyanide ions after standing for several months. Another similar reaction of... 

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. 

In addition to phenols, naphthols, their alkyl derivatives and the heterocyclic compounds mentioned above, a large variety of substituted monocyclic as well as condensed phenols have been subjected to the Reimer-Tiemann reaction. Although with a few exceptions the yields are only moderate, the facile reaction conditions, at least on a laboratory scale, have assured the reaction a permanent place among the variety of methods by which an aldehyde group can be attached to an aromatic nucleus. For example, phenolphthalein (1) has been formylated under standard Reimer-Tiemann conditions by van Kampen to yield the o-hydroxy aldehyde in 59% yield (equation 5)."... 

Electrophilic reactions on compound 2 produce 7-substituted derivatives. Thus, nitrosation, acylation, diazonium coupling, Reimer-Tiemann conditions or phosgenation of a substituted 2, produce 4 the corresponding 7-substituted derivatives shown in Eq. (39)... 

Methylpyrroles have been converted into pyridines by hydrochloric acid under severe conditions, and also by pyrolysis (p. 109). The formation of a 3-chloropyridine derivative from a pyrrole under Reimer-Tiemann conditions has been mentioned (p. 63). This type of reaction was discovered by Ciamician and Dennstedt treated pyrrole with chloroform in ether and isolated a small yield of 3-chloropyridine. Subsequently, similar reactions were realized with bromoform, carbon tetrachloride, methylene iodide and benzal chloride. Those of several of these reagents with lithium pyrrole in ether and sodium pyrrole under various conditions have been compared. The yields of pyridine derivatives were always low. In submitting 2,5-dimethylpyrrole to the Reimer-Tiemann reaction, Plancher and Ponti23 isolated a pyrrolenine (7). This and its analogues are not intermediates in the conversion of pyrroles into 3-chloropyridines. The idea that dichlorocarbene is the active reagent in reactions using chloroform is supported by recent work 22 ... 

Hydroxy-4-methylthiazole failed to react when submitted to Friedel-Crafts benzoylation conditions (349) on the other hand, it reacted normally in Gattermann and in Reimer-Tiemann formylation reactions, affording the 5-formyl derivative (348). 4-Methylthiazole is insufficiently activated and fails to react under the same conditions. 2,4-Dimethylthiazole undergoes perfluoroalkylation when heated at 200° for 8 hr in a sealed tube with perfluoropropyl iodide and sodium acetate (116) (358). 

Using Reimer-Tiemann reaction conditions on 3-alkyl-6-hydroxy-1,2-benzisoxazoles results in formylation occurring at the 7-position (77UC(B)1056). 

Under conditions more similar to those of the Reimer-Tiemann reaction 3-bromopyridine was obtained from pyrrole and bromo-form. Treatment of pyrrole with chloroform and aqueous alkali gave pyrrole-2-aldehyde curiously, the formation of 3-chloropyridine under these conditions does not appear to have been reported, in spite of being frequently quoted. However, indole gave both indole-3-aldehyde and 3-chloroquinoline under these conditions [Eq. (10)]. 

The structure of the product of the Reimer-Tiemann reaction of 1,2,3-trimethylindole (24) has been confirmed as 3-dichloromethyl-1,3-dimethyl-2-methyleneindoline (25) by spectroscopy and oxidation to the iV -methyloxindole when the dichlorocarbene was generated under neutral conditions a ring-expanded product, 3-chloro-1,4-dimethyl-2-methylene-1,2-dihydroquinoline (26) could be isolated and oxidized to the corresponding a-quinolone. These reactions presumably proceed by mechanisms similar to those discussed for 2,3-di-... 

Potassium phenoxide, which is less likely to form such a complex, " is chiefly attacked in the para position. " Carbon tetrachloride can be used instead of CO2 under Reimer-Tiemann (11-17) conditions. 

Under suitable conditions, this can be a useful preparative method for cyclopropanes another preparative trapping reaction of CC12 is its electrophilic attack on phenols in the Reimer-Tiemann reaction (p. 290). 

Because of the differential partitioning of hydroxide and phenoxide anions into organic solvents by quaternary ammonium cations, the catalysts generally have little effect on the Reimer-Tiemann reaction of phenols with dihalocarbenes [15]. Cetyltrimethylammonium bromide has been used in the two-phase dichloromethyl-ation of polysubstituted phenols (Scheme 7.21, Table 7.10) under Makosza s conditions [16,17] ring expansion of the reaction products provides an effective route to tropones. The rate of the reaction is enhanced by ultrasonic radiation [16]. 

Both the Reimer-Tiemann and the Vilsmeier reactions lead to formylation in the 5-position in pyrimidines with at least two strongly releasing substituents <1994HC(52)1>. The reaction of metallated intermediates with acyl electrophiles can be used to give acyl derivatives <2001T4489>, and direct carbamoylation of 6-aminouracil derivatives 87 has been achieved under microwave-assisted conditions to give 88 <2005S2713>. 

Under the conditions of the Reimer-Tiemann reaction, 2-methyl-1 //-pyrrolo[2,3-/>]pyridine (57) gave the aldehyde (58) without any ring-expanded products (Equation (9)) <68AHC(9)27>. 

M.E. Jung and co-workers have developed a synthesis of selectively protected L-Dopa derivatives from L-tyrosine via a Reimer-Tiemann reaction followed by the modified Dakin oxidation. The formyl group introduced by the Reimer-Tlemann reaction had to be converted to the corresponding phenol. After trying many sets of conditions, the Syper process was chosen, which uses arylselenium compounds as activators for the oxidation. Treatment of the aromatic aldehyde with 2.5 equivalents of 30% hydrogen peroxide in the presence of 4% diphenyl diselenide in dichloromethane for 18h gave the aryl formate in excellent yield. This ester was cleaved by treatment with methanolic ammonia for 1h to afford the desired phenol in good yield. 

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. 

Intriguing but confusing information is available in two Chemical Abstracts references to Chinese publications. A 1988 abstract d reports the behavior of phenol under Reimer-Tiemann reaction conditions with the addition of tertiary amines. The authors claim that the para. ortho ratio is reversed from that normally observed and 60% yield of p-hydroxybenzaldehyde, 7% yield of o-hydroxybenzaldehyde and only 1% tars are obtained when phenol is subjected to the new conditions. One year later a report appeared in which it is claimed that the use of tertiary amines under phase-transfer conditions increases the yield of ortho product. The authors report a yield of 79% of salicylaldehyde from phenol using 0.37% catalyst (the nature of the catalyst is not mentioned in the abstract and the Chinese publication is not available to this author), and 35% sodium hydroxide at 55-60 °C for 90 min. Surely, these results (or the translation) warrant checking. 

Ring expansion during Reimer-Tiemann reaction conditions on pyrroles and indoles to furnish pyrid-ines and quinolines was observed by Ciamician in 1881 (equations 13 and 14). Although a preparative reaction of little use due to the low yield, this transformation stimulated others to carry out ring expansion attempts on nonphenolic substrates with considerable success. ... 

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