Enamines from

Cycloadditions of diazaquinones with unsaturated compounds yield diazacyc-lobutanes, from which N-substituted 3-hydroxypyridazin-6(l/f)-ones are formed after addition of water, t-butanol or acetic acid (Scheme 56). The same types of compound are also obtained from enamines. 

The synthesis of a large number of y-pyrones and y-pyranols from enamines has been brought about through the use of a wide variety of bifunctional molecules. These molecules include phenolic aldehydes (126,127), phenolic Mannich bases (128), ketal esters (129), and diketene (120-132). All of these molecules have an electrophilic carbonyl group and a nucleophilic oxygen center in relative 1,4 positions. This is illustrated by the reaction between salicylaldehyde (101) and the morpholine enamine of cyclohexanone to give pyranol 102 in a quantitative yield (127). 

Aminocyclopropanes were prepared from enamines by the addition of Simmons-Smith reagent (688) or best through the cuprous-chloride-promoted decomposition of diazomethane (689). The reaction of an enamine with chloroform and base and opening of the resultant aminocyclopropane to an ynamine was reported (690). 

The intermediacy of ketenes in some enamine acylation reactions using acid chlorides was described above (386,387). Direct addition of ketene to enamines was studied simultaneously by several groups (414-420). The initially formed aminocyclobutanone products could be isolated in some instances, depending on the substitution of the initial enamine. Opening to give either the acylated enamine or the alternative vinylogous amide was found to occur spontaneously or on heating, particularly in adducts derived from enamines with an olefinic proton. 

Schiff s bases also underwent C or N acylation with isocyanates (698) and isothiocyanates (698,701). Further studies provided 2 1 and 2 2 reaction products of arylisothiocyanates and enamines (702) and polymers derived from enamines and bisisocyanates (703). 

Extension of the hydration reaction to hydrogen peroxide has shown that stable peroxides are formed from enamines and the imonium salts derived from secondary amines and ketones (506,507). 

One of the extensively investigated applications of enamines to heterocyclic syntheses is based on the bifunctional character of enamine acylation products. Thus the vinylogous ureas and thiorueas obtained from enamines and phenylisocyanate and phenylisothiocyanate (-433) have been converted to aminopyrazoles and thiouracils with hydrazine (566) and phenylisocyanate (567). 

Azatriquinadiene (2,3-dihydroazatriquinacene) 39 has been efficiently synthesized from enamine 389. Enamine 389 on treatment with bromine followed by aqueous work-up afforded the tetrabromohemiaminal 390. Dehydrohalogenation of 390 with potassium hexamethyldisilazide (KHMDS) and compound 391 on reduction with lithium aluminium hydride yielded the target molecule azatriquinadiene 39 in good overall yield (Scheme 85) <2000JOC7253>. 

Diacyl triafulvenes yield with enamines the 6-amino-5,6-dihydro-6aH-cyclo-penta(b)furans 524 of structure type A/B, type B is only obtained from enamines... 

For example, substituents in terminal olefins (43) in the resulting nitronates (35) are generally adjacent to the C-6 atom. The alkoxy and siloxy substituents from vinyl ethers and silyl enolates respectively, as well as the amino group from enamines, are oriented in the same positions. In the case of tris-substituted olefins, C-6 is the most crowded atom in the resulting nitronates. 

The preparation of dithianes from enamines by reaction with trimethylene dithiotosylate (propane-1,3-dithiol di-p-toluenesulfonate) has been applied with enamines derived from oholostan 3 one, aceto-acetic ester, and phenylacetone.6 7 Reactions of trimethylene dithiotosylate with hydroxymethylene derivatives of ketones also give rise to dithianes thus the hydroxymethylene derivative of cholest-4-en-3-one can be converted to 2,2-(trimethylenedithio)cholest-4-en-3-one. 1,3-Dithiolanes are obtained in a similar manner by reaction of ethylene dithiotosylate1 with the appropriately activated substrate.5,7... 

The present procedure is a general method for the preparation of monoalkylated ketones from enamines of aldehydes and ketones with electrophilic olefins. There are many advantages in this method of alkylation. Only monoalkylation occurs, even when such reactive species as acrylonitrile are used and, when a cyclic ketone like 2-methylcyclohexanone is used, reaction occurs only at the lesser substituted center. In a general base-catalyzed reaction, substitution occurs on the more substituted center. 

Cyclic analogues of hydrazones [151], 2-pyrazolines, show both protonation and alkylation on N-1, as has already been discussed on page 326. The sp nitrogen (which distinguishes these systems from enamines) does not appear to play any direct part. 

Mixtures of triazoles are obtained from enamines in which tauto-merism is possible. For example, addition is observed to both tautomers of enamines of the type 6 (Scheme 15). ... 

Macrocyclic 2-pyrones (113) and (114) are prepared from enamine (115) and ketene (75HCA2409). Reduction of cyano ketone (116) with LAH affords an amino ketone which spontaneously cyclizes to generate a tetrahydropyridine (117) dehydrogenation by palladium on charcoal produces the aromatized phane (118) (71TL671). 

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