Enamines sulfones

In a subsequent investigation by the author Step 2 analogues (1), UV-A enamine sulfonic acid derivatives, (I), and (II), were prepared and are described (I). 

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

Diazoalkanes add to the carbon-carbon double bonds of 2,3-diphenylthiirene 1-oxide and 1,1-dioxide. The adducts lose SO or SO2 to give pyrazoles and related compounds (Scheme 103) (80CB1632). Mesoionic oxazolones (75CLH53), 4-methyl-5-phenyl-l,2-dithiolene-3-thione (80JOU395) and pyrylium betaines (72JOC3838) react similarly via intermediate adducts (Scheme 104). Enamines (Scheme 96) and ynamines add to the double bond of 2,3-diarylthiirene 1,1-dioxides to give acyclic and cyclic sulfones by a thermal. 

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

However, when the bulky substituent is no longer present at the electrophilic carbon atom, the addition of the olefin to the morpholine enamine of cyclohexanone leads largely to the tetrasubstituted isomer. For instance the reaction of this enamine with phenyl vinyl sulfone gave a 1 3 mixture of... 

Reaction of the pyrrolidine enamine of cyclohexanone with phenyl vinyl sulfone afforded a 9 1 mixture of the tri- and tetrasubstituted isomers (2(5). The preference of the less substituted isomer in this case is in keeping with the greater overlap requirement between the n electrons of the double bond and the electron pair on the nitrogen atom, since the double bond exo to the five-membered ring is much more favored than the double bond exo to the six-membered ring. It is, however, hard to explain the formation of largely the trisubstituted isomer with the piperidine enamine of cyclohexanone, where both of the rings involved are six-membered. 

Stork and Borowitz (36) have reported that the reaction of the pyrrolidine enamine of cyclohexanone with aromatic sulfonyl chloride led to the tetrasubstituted isomer of the sulfonated enamine (63). 

The reaction with methanesulfonyl chloride in the presence of a proton abstracter like triethyl amine gave not the enamine, but a cyclic amino-sulfone (64). 

Additional evidence that a dynamic equilibrium exists between an enamine, N-hemiacetal, and aminal has been presented by Marchese (41). It should be noted that no acid catalysts were used in the reactions of aldehydes and amines discussed thus far. The piperidino enamine of 2-ethylhexanal (0.125 mole), morpholine (0.375 mole), and p-toluene-sulfonic acid (1.25 x 10 mole) diluted with benzene to 500 ml were refluxed for 5 hr. At the end of this time the enamine mixture was analyzed by vapor-phase chromatography, which revealed that exchange of the amino residue had occurred in a ratio of eight morpholine to one piperidine. Marchese proposed a scheme [Eqs. (4), (5) and (6)] to account for these... 

The enamines derived from cyclic ketones give the normal alkylated products, although there is some evidence that unstable cycloadducts are initially formed (55b). Thus the enamine (28) derived from cyclohexanone and pyrrolidine on reaction with acrylonitrile, acrylate esters, or phenyl vinyl sulfone gave the 2-alkylated cyclohexanones (63) on hydrolysis of the intermediates (31,32,55,56). These additions are sensitive to the polarity of the solvent. Thus (28) in benzene or dioxane gave an 80% yield of the... 

Alkyl sulfonyl chlorides, having an a-hydrogen atom, react with enamines derived from aldehydes and cyclic ketones in the presence of triethylamine to give cyclic sulfones. Thus the enamine (22) gave the four-membered cyclic aminosulfone (143) on reaction with methanesulfonyl chloride (95). 

In a similar manner the enamine (113) reacted with methanesulfonyl chloride (96) to give the cyclic sulfone (144). 

The formation of the same four-membered ring aminosulfone (145) from the enamine (22) and cyclohexanesulfonyl chloride in 72% yield and from N-(cyclohexylidenemethyl)pyrrolidine (146) and 2-propanesulfonyl chloride in 77 % yield proves the constitution of these cyclic sulfones (97). 

The reaction is postulated as proceeding via dehydrochlorination of the sulfonyl chloride to the sulfene, followed by cydoaddition to the enamine. The possibility that addition of the sulfonyl chloride to the enamine followed by dehydrochlorination, either directly or via the C-suIfonated enamine, results in the formation of the four-membered sulfone has been ruled out (98—100). 

Recently acyclic sulfones have also been isolated (99,101). Reaction of the enamine (28) with phenylmethane sulfonyl chloride (101) gave benzyI-2-oxocyclohexyl sulfone (147). 

The formation of acyclic sulfones is favored by increasing substitution at the a-carbon of the sulfonyl chloride and also of the enamine (97,100). 

The aromatic sulfonyl chlorides which have no a-hydrogen and thus cannot form sulfenes give acylic sulfones. Thus 1-piperidinopropene on reaction with benzene sulfonyl chloride (9J) gave 2-benzenesulfonyl-l-piperidinopropene (153). Similarly the enamine (28) reacts with p-toluene-sulfonyl chloride to give the 2-p-toluenesulfonylcyclohexanone (154) on hydrolysis (/OS). 

Methyl vinyl sulfone forms 1,2-cycloaddition adducts with aldehydic enamines, both with and without 3 hydrogens (37). Simple alkylation was reported to take place when phenyl vinyl sulfone was allowed to react with cyclohexanone enamines (58,60), but it has recently been shown that phenyl vinyl sulfone also forms cyclobutane adducts (60a). 

Enaminoketones undergo 1,4 cycloadditions with sulfene (162a). This is illustrated by the reaction of enamine 120 with sulfene to form sulfone 121 in an 80 % yield (162,163). 

Analogously, enamines substituted with nitrile (47,48), ester (49,50), sulfone (57), and nitro groups (52) were obtained. 

The addition of secondary amines to acetylenes is most applicable to the synthesis of conjugated acyclic enamines (50,171,172). Particularly the addition to acetylenic esters and sulfones has been investigated (173-177) and it appears that an initial trans addition is followed by isomerization to more stable products where the amine and functional group are in a trans orientation (178). Enamines have also been obtained by addition of secondary amines to allenes (179). 

The condensation of sulfonyl chlorides with enamines (452,453) derived from aldehydes and ketones has led to four-membered-ring sulfones, presumably through such intermediates (454-464). Open sulfonation products have also been obtained, particularly from ketone-derived enamines and from a-disubstituted sulfonyl chlorides. 

Arylsulfonyl chlorides and enamines reacted to give sulfonated enamines (452,453,474). The latter could be hydrolyzed to the corresponding sulfonyl ketones. 

Allylsulfonyl chloride and enamines furnished the sulfonyl enamines or cyclic sulfones 704), and alkyldisulfonyl chlorides gave 1 2 adducts or bicyclic products with morpholinocyclohexene. 

Thus, simple ketones or aliphatic aldehydes may be successfully used as starting materials in the CSIC (Carbanion mediated Sulfonate Intramolecular Cyclization) reaction. Ai-alkylsulfonamides could be also cyclized under CSIC conditions (99T(55)7625) affording the spiroisothiazoline 79. By treatment with TMSCl, Nal in acetonitrile at r.t., hydrolysis of the enamine and formation of the corresponding keto derivative 80 was obtained. 

The reaction of the enamines of cyclohexanones with a,ft-unsaluraled sulfones gives mixtures resulting from attack of the enamine at the a- and /(-carbons of the oc,/ -unsaturated sulfone. The ratio of x- and /1-adducts is dependent upon the reaction solvent, the geometry and structure of the sulfone1 4. The diastereoselectivity of these reactions is also poor. The reaction of lithium enolates of cyclic ketones with ( )-[2-(methylsulfonyl)ethenyl]benzene, however, gives bicyclic alcohols, as single diastereomers, that result from initial -attack on the oc,/ -unsaturated sulfone5. 

It appears, however, that the most used strategy for the preparation of thietane dioxides is the [2 + 2] cycloaddition of enamines (202) with in situ-generated sulfenes (220)74,143,186 188,202,242 to give /(-aminothietane sulfones (equation 85). 

Practically speaking, almost all syntheses of these systems are based on the enamine-sulfene cycloaddition reaction143 250. The thietane sulfone thus obtained yields, by elimination of R2NH, the desired unsaturated, four-membered sulfone system187 189 231 250 251 (equation 87). 

Similarly, enamino vinyl sulfones (345) can undergo a thermally allowed electrocyclic reaction between the termini of the enaminic double bond and the allyl sulfonyl portion in the intermediate anion (346) to afford a, /1-unsaturated thiene dioxides (348) as shown in equation 126335. 

Vinyl sulfones, being good Michael acceptors, have been regarded as useful reagents for carbon-carbon bond formation. Nucleophiles used often are organometallic reagents, enamines and enolate anions and the Michael addition products are usually obtained in... 

Among other methods for the preparation of alkylated ketones are (1) the Stork enamine reaction (12-18), (2) the acetoacetic ester synthesis (10-104), (3) alkylation of p-keto sulfones or sulfoxides (10-104), (4) acylation of CH3SOCH2 followed by reductive cleavage (10-119), (5) treatment of a-halo ketones with lithium dialkyl-copper reagents (10-94), and (6) treatment of a-halo ketones with trialkylboranes (10-109). 

The preparation and investigation of the thietane oxide system (5a) is largely associated with stereochemical and conformational studies . The investigation of the thietane dioxides (5b) is substantially related to the chemistry of sulfenes , the [2 -I- 2] cycloaddition of which with enamines is probably the method of choice for the synthesis of 5b . The study of the thiete dioxide system (6) evolved, at least in part, from the recognition that the unstable thiete system 183 can be uniquely stabilized when the sulfur in the system is transformed into the corresponding sulfone , and that the thiete dioxide system is very useful in cycloadditions and thermolytic reactions. The main interest in the dithietane oxides and dioxides (7) appears to lie in the synthetic challenge associated with their preparation, as well as in their unique structural features and chemical behavior under thermolytic conditions . ... 

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