Picolin aldehyde

Method 2. This method has been used widely in various modifications since its early introduction for the synthesis of ciyptopleurine (18) 47). It is related to method 1, but instead of picolinic aldehyde, it employs an ester of... 

In the case of the 2-picolinic aldehyde shown in Eq. (1-6), the only catalytic system that gave polymer was potassium im-butoxide in dimethyl sulfoxide (53). 

Chemical Designations - Synonyms Aldehyde-collidine Aldehydine 5-Ethyl-2-Methylpyridine 5-Ethyl-2-picoline MEP Chemical Formula CjHnN. 

The use of silver (II) salts, particularly argentic picolinate, as reagents for hydroxyl oxidation has also been disclosed recently. The reaction may be run in acid, neutral or basic media in aqueous or polar organic solvents at room or slightly elevated temperatures. Primary alcohols may be oxidized to aldehydes or acids depending on the conditions used. Amines and trivalent phosphorous compounds are more sensitive to oxidation with this reagent than are hydroxyl groups. 

Besides direct reduction, a one-pot reductive amination of aldehydes and ketones with a-picoline-borane in methanol, in water, and in neat conditions gives the corresponding amine products (Scheme 8.2).40 The synthesis of primary amines can be performed via the reductive amination of the corresponding carbonyl compounds with aqueous ammonia with soluble Rh-catalyst (Eq. 8.17).41 Up to an 86% yield and a 97% selectivity for benzylamines were obtained for the reaction of various benzaldehydes. The use of a bimetallic catalyst based on Rh/Ir is preferable for aliphatic aldehydes. 

Ammonia or an amine can also be introduced between a terminal aldehyde or a ketone and a suitably placed double or triple bond, although the method is of limited use. A poor yield of 4-picoline is obtained when the aldehyde (262) is treated with ammonia or an ammonium salt (49JCS1430) and dihydroquinolines from the phenylethyl ketones (263) and hydroxylamine (76MI20800). More commonly, cyclization occurs by insertion of ammonia, amines or hydroxylamine between two triple or double bonds in the former case, pyrid-4-ones (264) are obtained (54BSF734) in the latter, a piperid-4-one (265) results (1897CB231). Amines have also been used to give N -substituted piperid-4-ones (70OMR(2)197>. In these cases a double 1,4-addition must be involved in the cyclization of the unsaturated nitrile... 

Synthetic Methods of Manufacture. Due to rising demand, production of the pyridine bases by large-scale synthesis passed the volume of tar bases extracted from coal tar in the 1960s. By the early 1970s. capacity in the United States for the synthetic manufacture of pyridine, the picolines, and 2-methyl-5-ethylpyridine (MEP) was in the tens of millions of pounds. All of these products can be made by condensation reactions of aldehydes and ammonia, MEP is no lunger made in the United Stales,... 

Such reactions are, however, not unexpected, as the reactivity of the methyl groups in 2- and 4-picolines is well documented, as exemplified by their condensation with aromatic aldehydes to give trans 2- and 4-styrylpyridines.82... 

Macroscale reduction of the monoacids 56 could lead to a variety of products, depending on the extent of electrolysis. For instance, reduction to the carbinols (29-31) would seem likely further reduction might also give the picolines 15, 16, and 19. Reduction of the picolines could also give the piperidines or piperdeines (see Schemes 5 and 10). Experimentally, all of these processes have been observed at one time or another in addition to formation of the isomeric aldehydes 41,42, and 58. 

Reduction of 4-(65) gave aldehyde 42 in strong acid and carbinol 31 in acetate buffer.99 In alkaline electrolyte, 31 would be further reduced to the picoline (19) (Scheme 19). The IV-phenylamide gave a mixture of the carbinol... 

Aldehyde 1 (0.2 mmol), alkene 2 (1.0 mmol), 2-amino-3-picoline (0.08 mmol), benzoic acid (0.02 mmol) and RhCl(PPh3)3 (0.01 mmol) were mixed in the absence of any organic solvent and then submitted for 10 min to microwave irradiation inside a domestic microwave oven (Samsung, RE-431H, 700 W) or in a monomode Syntliewave 402 Prolabo where power is enslaved to temperature at 140 °C. After the reaction, the product 3 was purified by column chromatography 38-85%. 

Styryl dyes for dyeing paper in brilliant shades are derived from quatemized y-picoline. The dye 25 obtained by reaction with 4 - (N- e thy 1 - A - b c n zy 1 am in o) be n z-aldehyde has a brilliant orange color [58],... 

A primary alcohol and amines can be used as an aldehyde precursor, because it can be oxidized by transfer hydrogenation. For example, the reaction of benzyl alcohol with excess olefin afforded the corresponding ketone in good yield in the presence of Rh complex and 2-amino-4-picoline [18]. Similarly, primary amines, which were transformed into imines by dehydrogenation, were also employed as a substrate instead of aldehydes [19]. Although various terminal olefins, alkynes [20], and even dienes [21] have been commonly used as a reaction partner in hydroiminoacylation reactions, internal olefins were ineffective. Recently, methyl sulfide-substituted aldehydes were successfully applied to the intermolecu-lar hydroacylation reaction [22], Also in the intramolecular hydroacylation, extension of substrates such as cyclopropane-substituted 4-enal [23], 4-alkynal [24], and 4,6-dienal [25] has been developed (Table 1). 

Carboxylic acids can be reduced in acid solution to alcohols, aldehydes, or hydrocarbons 7<9 Polarographic and epe studies on the cathodic reduction of isonicotinic acid in weakly acid solution (pH about 3.1 M aqueous potassium chloride) have shown that the product, 4-pyridinealdehyde, exists as a hydrate in aqueous medium and that the hydrate does not undergo further cathodic reduction 137 The same applies to reduction of picolinic acid 137 imidazole-2-car-boxylic acid 138 and 2-thiazolecarboxylic acid 13 9. In the last case the yield of aldehyde was fairly low, probably due to competing reduction of the thiazole ring. It was concluded 139 that the following requirements must be fulfilled for the facile reduction of a carboxylic acid to the aldehyde stage to take place ... 

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