Enamines, reactions, carbon disulfide

The cycloaddition reaction of carbon disulfide to a carbon-carbon double bond was first observed by Mumm and coworkers in 1939. The authors obtained 1 1 adducts from enamines and carbon disulfide. The initially formed cycloadducts rearrange to form linear adducts 19 because of the availability of j8-hydrogen atoms. 

A by-product of the reaction between an enamine, elemental sulfur, and carbon disulfide is an a-dithiopyrone. This by-product is the result of the condensation of two enamine molecules with one carbon disulfide molecule. In the case of aldehydic enamines, the reaction probably proceeds through... 

The formation of a-dithiopyrone by-products during the reaction of an enamine with elemental sulfur and carbon disulfide is enhanced by one or a combination of the following the carbon disulfide is allowed to stand for a long period of time with the enamine in the absence of sulfur, a high reaction temperature, and the use of a relatively nonpolar solvent (135). 

From the reactions of sulfur and carbon disulfide with cyclic ketone-derived enamines (570-573) 3H-l,2-dithiole-3-thiones were obtained, whereas the addition of carbon disulfide to other enamines gave a-dithio-pyrones (574), through initial dimerization of the enamine. 

A different route to pyrones is the preparative electrochemical oxidation of enamines in acetonitrile in the presence of tetraethylammonium perchlorate (88MI2) (Scheme 46). The synthesis of 2-pyrone derivatives has been carried out by reaction of /3-dicarbonyl compounds with methyl-a-benzoylamino-/3-dimethylaminoacrylate (96JHC751). Thiapyran derivatives can be obtained by interaction of enamines based on (/3-amino-a-cyanoacryloylmethyl)pyridinium chloride derivatives with carbon disulfide (95M711).The synthesis of pyridine derivatives based on analogous enamines has been described as well (95M711). 

Recently it has been reported that a-thio derivatives of enamines and enol ethers form 5-amino- or 5-alkoxy-l,2-dithiole-3-thiones (127a, b) by reaction with carbon disulfide (80ZOR13). Spiran compounds (128) are also formed from suitable substrates. The reaction has some similarities to an enamine synthesis below <67AG(E)294). 

The readily accessible enamines react with carbon disulfide and sulfur under mild conditions to produce l,2-dithiole-3-thiones (3b) via 3-amino dithioacids (Scheme 24), The nucleophilic character of the enamines is necessary for the initial reaction and to activate the sulfur (from Sg) for further insertion (67AG(E)294). Modified procedures produce other heterocycles. The yields of thiones (3b) may be low but this versatile reaction produces thiones that may be otherwise difficultly accessible, especially by direct sulfurization procedures, e.g. 1-morpholinocyclohexene may be converted into tetrahydrobenzo-1,2-dithiole-3-thione (142) in 40% yield. By contrast, direct sulfurization of 1-methylcyc-lohexene gives benzo-l,2-dithiole-3-thione (77b). Even dihydronaphtho-l,2-dithiole-3-thione (143) may be made by this procedure, although this compound may be dehydrogenated readily by sulfur at 220 °C. 

Action of Carbon Disulfide on Enamines and Dienamines Simple a-dithiopyrones (8), until recently hard to prepare and therefore inadequately investigated, are now available by a generally applicable and as a rule very efficient procedure, the one-step reaction of enamines of type 30 or 31 with carbon disulfide.42,43,46,47 The reaction should be carried out in a polar solvent at room temperature. 

In the case of monomeric aldehyde enamines (31), it was possible to show that the products are formed via the dienamine (32) which can be converted directly with carbon disulfide, requiring a shorter reaction time and giving higher yields.43 Starting from the dienamine (32) (R = H) the parent compound (8) is formed the yield, however, is maximally about 10%.43... 

Enamines give 1,2-dithiole-3-thiones with carbon disulfide and sulfur.80 The reaction of aniline (44) described in Eq. (2) gives l,2-dithiole-3-thiones (7) as by-products along with pyrrole (45).81... 

Enamines react with carbon disulfide and elemental sulfur to give l,2-dithiole-3-thiones via 3-iminodithioic acids <82AHC(3l)63>. The reaction can give other products and the yields are rather low, but the mild conditions of the reaction, contrasted with thermal reactions of elemental sulfur, do not cause dehydrogenation. Thus, 1-morpholinocyclohexene gives tetrahydrobenzo-l,2-dithiole-... 

There is almost no restriction in the choice of an appropriate electrophile in the Knoevenagel reaction. Aldehydes, ketones, thioketones, imines, enamines, acetals and orthoesters have been used. With less reactive methylene groups, however, drastic reaction conditions may be necessary. Steric effects have a significant influence on the rate and unexpected compounds are often obtained as a result of secondary reactions. Reaction of 1,3-dicarbonyl compounds with carbon disulfide followed by dialkylation with an alkyl halide give diacylketene-S,5-acetals (159). However, even with highly acidic dicarbonyl com-... 

Reaction of N-aryl-enamine 31 with excess of carbon disulfide in the presence of sodium hydroxide followed by dimethylsulfate afforded the... 

The Schiff base or enamine reaction has been employed to modify aldehydes and ketones by condensation with a primary amine (reaction 1) and to condense primary amines with a carbonyl compound (reaction 2). A similar reaction between primary amines and carbon disulfide yields isothiocyanates or mustard oils (reaction 3). These three possibilities for derivative formation will be discussed in this chapter. 

Ketimines react with carbon disulfide similarly to afford linear 1 1 adducts When the reaction of enamines or ketimines with carbon disulfide is conducted in the presence of elementary sulfur, the flve-membered ring heterocycles 20 are obtained. ... 

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