Initiators condensation

This reaction consists of the condensation of two molecular equivalents of a 1,3 diketone (or a J3-keto-ester) with one equivalent of an aldehyde and one of ammonia. Thus the interaction of ethyl acetoacetate and acetaldehyde and ammonia affords the 1,4-dihy dro-pyridine derivative (1), which when boiled with dilute nitric acid readily undergoes dehydrogenation and aromatisation" to gb e the diethyl ester of collidine (or 2,4,6-trimethyl-pyridine-3,5 dicarboxylic acid (II)). For the initial condensation the solid aldehyde-ammonia can conveniently be used in place of the separate reagents. 

This, the Darzens reaction, is useful in other circumstances (frames 280-1) but a nuisance here. We must use some means to make the ketone act as the nucleophile in the initial condensation. One effectiye way is to conyert it into an enamine. Draw a mechanism for this reaction. 

Note that the 14 ppm of ammonia measured in the accumulated condensate may not accurately reflect the potentially higher level of ammonia dissolved in a thin film of moisture that could form on the metal wall in the region of initial condensation. This film of water could be saturated witb ammonia, increasing susceptibility of the metal to SCC. 

This reaction, like the initial condensation, is favoured by acidic conditions and peroxides are ineffective. 

The same chemical mechanisms and driving forces presented for phenol-formaldehyde resins apply to resorcinol resins. Resorcinol reacts readily with formaldehyde to produce resins (Fig. 2) which harden at ambient temperatures if formaldehyde is added. The initial condensation reaction, in which A-stage liquid resins are formed, leads to the formation of linear condensates only when the resorcinol/formaldehyde molar ratio is approximately 1 1 [119]. This reflects the reactivity of the two main reactive sites (positions 4 and 6) of resorcinol [120]. However, reaction with the remaining reactive but sterically hindered site (2-positiori) between the hydroxyl functions also occurs [119]. In relation to the weights of resorcinol-formaldehyde condensates which are isolated and on a molar basis, the proportion of 4- plus 6-linkages relative to 2-linkages is 10.5 1. However, it must be noted that the first-mentioned pair represents two condensa-... 

The Schlittler-Muller variation of the Pomeranz-Fritsch reaction involves reaction of diethoxyethanal 17 with benzylamine 16 to prepare the desired imine 18. Intermediate 18 is subsequently cyclised to substituted isoquinoline 19. The advantage here lies in the fact that the initial condensation can still take place between an aldehyde and an amine. 

There is some debate in the literature as to the actual mechanism of the Beirut reaction. It is not clear which of the electrophilic nitrogens of BFO is the site of nucleophilic attack or if the reactive species is the dinitroso compound 10. In the case of the unsubstituted benzofurazan oxide (R = H), the product is the same regardless of which nitrogen undergoes the initial condensation step. When R 7 H, the nucleophilic addition step determines the structure of the product and, in fact, isomeric mixtures of quinoxaline-1,4-dioxides are often observed. One report suggests that N-3 of the more stable tautomer is the site of nucleophilic attack in accord with observed reaction products. However, a later study concludes that the product distribution can be best rationalized by invoking the ortho-dinitrosobenzene form 10 as the reactive intermediate. 

A tetracyclic heterocycle that bears little relation to any clinically used drug has been described as an antiinflammatory agent. The compound is prepared in rather straightforward manner by initial condensation of dihalide 143 with 1,2-diaetcylhydrazine. Hydrolysis of this product... 

A common case where intense general corrosion is experienced in a very restricted section of plant is where an acidic vapour is condensing. As a vapour the acid is usually non-corrosive, but when condensed it can only be handled in expensive materials. Another variation on this theme is that only at the region of initial condensation is there a corrosion problem, either the condense/reboil condition being particularly corrosive or else corrosion only takes place at or near the boiling point. Several variations in design are possible to cope with these situations ... 

Phenylcyclopent[c]azcpine (33a) and 6,7-fused cyclopentazepines 33b-d are formed in moderate yields in a one-pot, two-stage process involving initial condensation of triphenyl-[(l-phenylvinyl)imino]phosphoranes 32 with 6-(dimethylamino)fulvene-2-carbaldehyde (30), followed by an intramolecular aza-Wittig reaction of the iminophosphorane with the pendant aldehyde function.5 The method fails with the unsubstituted vinylphosphorane 32 (R1 = R2 = H). 

Schemes based on the acid-catalyzed condensation of a bipyrrole with a dipyrrylmethane are in general unsuccessful for the synthesis of corroles. Thus, the bipyrroles 1 fail to give corroles when reacted with the appropriate dipyrrylmethane 2.10,11 However, cobalt(III) corrole 3 can be prepared in moderate yield by a [2 + 2] approach involving bipyrrole T and dipyrrylmethane 2 bearing formyl groups and carboxylic groups, respectively, and heating initial condensation products, presumably norbilenes, with cobalt(II) acetate and triphenylphosphane in methanol.12...

NOTE When a boiler first starts up from cold, there is always some initial condensation arising from combustion (which generally falls to the rear of the boiler and may form a pool of water). This quickly evaporates and should not be confused with tube leaks that leave evaporated solids behind. 

Fewer procedures have been explored recently for the synthesis of simple six-membered heterocycles by microwave-assisted MCRs. Libraries of 3,5,6-trisubstituted 2-pyridones have been prepared by the rapid solution phase three-component condensation of CH-acidic carbonyl compounds 44, NJ -dimethylformamide dimethyl acetal 45 and methylene active nitriles 47 imder microwave irradiation [77]. In this one-pot, two-step process for the synthesis of simple pyridones, initial condensation between 44 and 45 under solvent-free conditions was facilitated in 5 -10 min at either ambient temperature or 100 ° C by microwave irradiation, depending upon the CH-acidic carbonyl compound 44 used, to give enamine intermediate 46 (Scheme 19). Addition of the nitrile 47 and catalytic piperidine, and irradiation at 100 °C for 5 min, gave a library of 2-pyridones 48 in reasonable overall yield and high individual purities. 

An efficient two-step annelation of functionalized orthoesters with trimethyl-silyloxyfuran derivatives has been reported that produces bicyclo[3. .0]lactones. ° The reaction in Scheme 7 shows an example in which the initial condensation between silyl enol ether and orthoester is followed by the radical cyclization reaction under standard conditions. It is worth underlining the complete diastereocontrol in which three contiguous stereocenters are generated in one step with >95% stereoselectivity. 

Uniformly labeled 2,4-dichlorophenol- C (purchased from New England Nuclear Corp, Boston, Mass.) was used in the tracer preparation. This provided a label at all carbon positions in the dibenzo-dioxin structure. 2,7-Dichlorodibenzo-p-dioxin- C after initial cleanup by fractional sublimation, contained approximately 5% of an impurity, detected by thin layer chromatography (TLC) which gave mass peaks at 288, 290, 292, and 294 in the mass spectrometer, consistent with a trichloro-hydroxydiphenyl oxide. This is probably the initial condensation product of the Ullman reaction and is most likely 2-(2,4-dichlorophenoxy)-4-chlorophenol. It was removed easily by extractions with aqueous... 

A useful method to synthesize ten and fourteen-membered ring imides 346 involved an initial condensation of macrocyclic -ketoestes 343 with alkyl or aryl isocyanates and carbodiimides, respectively, in the presence of a base [68]. After a nucleophilic attack of the enolate on the isocyanate C, the resultant amide N anion 344 induced a ring closure by addition to the keto group. Then, the intermediately formed four-membered ring 345 underwent a fragmentation... 

The initial condensation is best carried out at tr.-, ester oxidation level to take advantage of the Reformatsky method of control. Oxalic acid hydrolyst-s (36) to (31) without moving the double bond into conjugation. ... 

The first compounds of this class46 have been obtained via Route A. The initial condensation of phthalic anhydride with dimethylaniline requires a Friedel-Crafts catalyst, while condensation of the resulting benzophenone with the indole requires acetic anhydride. For Route B preparation of the intermediate l,2-dimethyl-3-(2-carboxybenzoyl)indole has also been described47 by condensation of the two components in the presence of aluminum chloride. However, in our experience, aluminum chloride is, in this case, unnecessary, thus rendering this route the method of choice. 

In analogy to the original preparation of Malachite Green lactone, pyromellitic anhydride has also been reacted with N, Ar-di me thy laniline in a zinc chloride melt to yield mixtures of the bisphthalides 29 and 30.109 However, far superior yields were obtained if reaction was carried out in two steps, as described in Scheme 12. The initial condensation was carried out... 

Azines have been prepared by initial condensation of diethoxyphosphinyIhydrazine anions with aldehydes or ketones (Scheme 9). Phosphoryl azides undergo 1,3-dipolar cycloaddition to 2-tetralone enamines to give triazolines, possibly en route to amidines. A full paper on the addition of diethyl dibromophosphoramidate to alkenes(leading to the synthesis of 2-bromoalkylamines) has appeared. ... 

Nitromethylation of aldehydes has been carried out in a one pot procedure consisting of the Henry reaction, acetylation, and reduction with sodium borohydride, which provides a good method for the preparation of l-nitroalkanes.16b 79 It has been improved by several modifications. The initial condensation reaction is accelerated by use of KF and 18-crown-6 in isopropanol. Acetylation is effected with acetic anhydride at 25 °C and 4-dimethylaminopyridine (DMAP) as a catalyst. These mild conditions are compatible with various functional groups which are often... 

The carbanion generated from deprotonation of the w-carbon atom of sulpholene reacts with aldehydes and ketones to give alcohols. Sulphur dioxide extrusion from the products results in (E)-a-hydroxy-l,3-dienes (equation 72), or dehydration followed by thermal desulphonylation results in trienes117. Dienones can be obtained if the initial condensation is conducted with an aldehyde, followed by oxidation and sulphur dioxide removal117. 

Bassin et al. reported a convenient synthesis of 3-methylsulphonamido-l,2-benzisothiazole-1,1 -dioxide 15 from 14 via initial condensation with ammonia followed by an internal Michael reaction <00JHC181>. 

Stilbene dyes are mixtures of indeterminate constitution resembling polyazo direct dyes in their application properties. They result from the alkaline self-condensation of 4-nitrotoluene-2-sulphonic acid (1.5) or its initial condensation product (1.6 X = N02),... 

FIGURE 8.15 Protein encapsulation in a silica matrix via sol-gel processing the process include (a) formation of the sol particles during hydrolysis and initial condensation, (b) addition of the protein into the sol solution, and (c) the growing silica network entraps the protein molecule. (Reprinted from M. Kato et al. Anal. Chem., 74 1915 (2002). With permission. Copyright American Chemical Society 2002.)... 

One-electron reduction of unsaturated a,8-diketones may sometimes generate a diene structure and initiate condensation. Thus, triazoledions (TAD) pass into tetraazabicyclooctanetetraones (TABO). Naphthalene-sodium (ca. 1 mol%), sodium metal, or even sodium iodide efficiently catalyzes the reaction. Tetracyanoethyene and lead tetraacetate retard it. Consequently, the condensation has a chain character (Borhani and Greene 1986 Scheme 7.30). 

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