Recent trends in synthesis of five- and six-membered heterocycles using dimethyl N-cyanodithioiminocarbonate
-
Galal H. Elgemeie
and
Reham A. Mohamed
Abstract
New approaches to synthesis of five- and six-membered heterocyclic compounds utilizing dimethyl N-cyanodithioiminocarbonate are surveyed. The scope and limitation of the most important approaches are discussed.
Introduction
Dimethyl N-cyanodithioiminocarbonate (1) is a highly reactive compound that plays a key role in the synthesis of a wide variety of heterocycles. The cyano and methylthio functions of this compound enable reactions with common bidentate reagents to form heterocyclic compounds. The active double bond of this compound can take part in a variety of addition reactions. Besides its importance as synthetic imtermediates, its derivatives are endowed with biological activity. In particular, diverse biological activities have been reported for many derivatives of 1 and have also drawn an immense interest of biochemists over the past decade. Compound 1 is a precursor to cyanoguanidines, to protein tyrosine kinase inhibitors, particulary compounds that function as inhibitors of c-fms kinase [1], to tricyclic N-cyanoimines useful as inhibitors of farnesyl-protein transferase [2], and heterocyclic GABA-B modulators [3]. Compound 1 is also a starting material in the synthesis of cannabinoid receptor ligands [4, 5], antiseptics [6], inhibitors of various enzymes [7, 8], antibacterial amidinomethyl- and guanidinomethyl-oxazolidinones [9], cancer metastasis inhibitors [10, 11], a metformin derivative [12], 5-HT2B receptors antagonists [13, 14], agmatine derivatives [15], guanidine derivatives [16], herbicides, crop [17], and plant growth regulators [18–22], potassium channel-activating agents that are useful as cardiovascular drugs, especially as anti-ischemic drugs [23, 24]. Additional syntheses of biologically active compounds from 1 have been described [25–36]. Despite the enormous literature on this compound, to our knowledge, no recent attempt to survey its wide range of chemical reactivity has been made. The present review is intended to fill this gap. It should be, however, stated clearly that it was not our plan to make an encyclopedic scan of the subject. Some reports were not included because they seemed to be a repetition of the established chemistry. Meanwhile, some of the old literature was included to better appreciate the chemistry and importance of this class of compounds.
Synthesis
The most common method to access dimethyl N-cyanodithioiminocarbonate (1) involves the reaction of cyanamide with carbon disulfide in the presence of alkali metal hydroxide in aqueous ethanol [37]. The intermediate dialkali metal salt of N-cyanodithioiminocarbonic acid (2) is then alkylated with methyl iodide [38, 39] or dimethyl sulfate [40] (Scheme 1).
A cyclic cyanodithioiminocarbonate, which is a growth-regulating agent, can be prepared by reacting dipotassium cyanodithioiminocarbonate (2) with a dibromoalkane [41]. It has been discovered that the water-soluble alkali and alkaline-earth metal salts of cyanodithioiminocarbonic acid are bactericidal and they are useful in preventing the formation of slime in pulp and paper mills and generally in preventing microbiological deterioration of a large variety of organic substances [42]. Such salts are also used to control sulfate-reducing bacteria [43] and find applications as industrial biocides in the manufacture of pulp paper [44] and paperboard products that are used in food packaging [44–46].
Utility in heterocyclic synthesis
Disubstituted N-cyanodithioiminocarbonates are used extensively as intermediates in heterocyclic synthesis [35]. They are precursors to pyrimido[6,1-a]isoquinolin-4-ones [47], substituted quinolones [48], pyridyl carboximide compounds useful in treating high blood pressure [49], guanidino-substituted benzopyrans [50], [1,2,4]-triazolo[1,5-a][1,3,5]triazines [51], bicyclic heterocyclic substituted phenyloxazolidinone antibacterials [52], benzenesulfonamide derivatives [53], imidazolidonones [54], fused heterocyclic compounds useful as kinase modulators [55], substituted methyl benzoate esters [56], imidazo[4,5-c]pyrimidines(purines) [57], 7-amino-2-(2-furyl)-5-methylthiopyrazolo[2,3-a][1,3,5]triazines [58], pyrazolo[2,3-a][1,3,5]triazines [58, 59], 2-furyl-triazolo[1,5-a]-[1,3,5]triazines [59], aryl-substituted 6-methylthiol-4-pyrimidones [60], the (S)-4-diphenylmethyl-NCT agent [61], substituted benzopyrans and related compounds [62], triazoles [63, 64], oxazoles [64], other azoles [65, 66], 5-O-desosaminylerythronolide derivatives [67], N-cyano-N′-alkyl-N″-2-mercaptoethylguanidines [68], dimeric phosphoaramidites [69], and cyanoguanidines [70].
Five-membered heterocycles
Five-membered rings with two heteroatoms
As shown in Scheme 2, compound 1 reacts readily with primary and secondary amines to give N-cyanoguanidines. For example, the reaction of 1,2-diaminoethane with 1 proceeds readily in benzene at reflux temperature and affords the imidazolidine 4 [71].
The synthesis of the imidazolidine, oxazolidine, and thiazolidine derivatives 7 is outlined in Scheme 3 by the reaction of 1 with secondary amino compounds 5 in refluxing ethanol solution. Products 7 are obtained by cyclization of the intermediate products 6 [72] (Scheme 3).
To obtain the imidazole derivative 10, methylaminoacetonitrile (8) was allowed to react with 1. The intermediate product 9 was isolated and then cyclized to 10 in the presence of sodium ethoxide [73] (Scheme 4).
It has been reported that the reaction of 1 with ethyl aminoacetate derivatives 11 in the presence of a base gives compound 12, which can be reacted with primary amines to afford the imidazolidinones 13 (Scheme 5) [74].
In the synthesis of the thiazole derivatives 17, compound 1 is allowed to react with secondary amines 14 in refluxing ethanol to afford isothioureas 15, the subsequent reaction of which with methyl mercaptoacetate is followed by thermolysis of the intermediate product 16 (Scheme 6) [75].
2-Cyanoiminothiazoldines 20 were prepared by the reaction of 1 with mercaptoamine derivatives 18 in refluxing dimethylsulfoxide (DMSO), via cyclization of the intermediate product 19 (Scheme 7) [76].
The reaction of 1 with amino compounds 21 in the presence of a base affords the 2-cyanoiminothiazolidine and 2-cyanoiminooxazolidine, respectively, 23a,b; compounds 22 are the suggested intermediates. Treatment of compounds 23 with 2-bromoethyl nitrate affords the substituted products 24 (Scheme 8) [77].
Sulfoximides 25 undergo a reaction with 1 to give compounds 26. Treatment of 26 with methyl mercaptoacetate in triethylamine affords thiazole compounds 27 (Scheme 9) [78–81].
The reaction of 1 with trimethylsilylemethylamine 28 yields the adducts 29. Treatment of 29 with cesium fluoride generates intermediate products 30, which in the presence of hetero dipolarophiles such as carbonyl compound 31a (X=O) and thiocarbonyl compounds 31b (X=S) undergo a 1,3-dipolar cycloaddition to yield 2-iminooxazolidines and 2-iminothiazolidine 32a,b (Scheme 10) [82].
Similarly, the 4,5-dihydro-2-iminooxazoles 34a and 4,5-dihydro-2-iminothiazoles 34b can be prepared by treatment of compounds 30 with formaldehyde 33a or thioformaldehyde 33b as shown in Scheme 11 [83–85].
The reaction of 1 with methyl mercaptoacetate in the presence of ammonium carbonate and potassium hydroxide affords 2-(N-cyanoiminothiazolidin)-4-one derivatives 35 (Scheme 12) [86].
The oxazolidine derivatives 37 are obtained by the reaction of compound 1 with 2S-amino-1S-p-nitrophenyl-1,3-propanediol 36 in refluxing ethanol (Scheme 13) [87].
Five-membered rings with three heteroatoms
The reaction of compound 12, derived from 1 and 11, with hydrazine hydrate or hydroxylamine hydrochloride affords the triazole 38 or the oxadiazole 39, respectively (Scheme 14) [74, 88].
In a similar way, the reaction of 1 with substituted hydrazines in refluxing ethanol for 5 h affords the substituted triazoles 40 (Scheme 15) [89–91].
1,2,4-Triazoles-3,5-diamines 44 were obtained as shown in Scheme 16. When the intermediate product 41 was allowed to react with silver nitrate and triethylamine in N,N-dimethylformamide, N-cyanocarbodiimide 42 was generated. Although the intermediate compound 42 could not be isolated, subsequent addition of 4-chlorophenylhydrazine to the solution yielded the 1,2,4-triazole-3,5-diamine 44. All attempts to prepare 44, by reaction of 43 with amine or by reaction 41 with aryl hydrazine were unsuccessful (Scheme 16) [92].
Reaction of 1 with benzalmethylhydrazone derivatives in the presence of a base affords compound 45, the reaction of which with a diamine 46 yields the 1,2,4-triazole compound 47 (Scheme 17) [93].
Reaction of 1 with different alkyl, aralkyl, and aryl hydrazines to yield 1-substituted 3-R-thio-5-amino-1H-1,2,4-triazoles 48 and 2-substituted 3-R-thio-5-amino-2H-1,2,4-triazoles 49 was studied. The reaction involves a nucleophilic attack on one of the hydrazino nitrogen atoms against the central and probably the most nucleophilic carbon atom of 1 to form 48 and 49 (Scheme 18) [94–102].
The reaction of methylhydrazine with 1a and 1c predominantly resulted in displacement of a methylthio group by the more nucleophilic substituted nitrogen atom and attack of the cyano function by primary amine to afford the 3-aminotriazoles 50 and 53 and the respective minor byproducts 51 and 52. Meanwhile, the reaction of methylhydrazine with 1b leads to the isomeric amino triazole 51 instead of the regoisomer 53. The structure assignment of 52 was confirmed by X-ray crystallographic analysis of the benzene sulfonyl isocyanate adduct 55 derived from 52 and 54 (Scheme 19) [72, 103–108].
The reaction of 1-(p-methylbenzyl)piperazine (56) with 1 in refluxing ethanol afforded a disubstituted piperazine 57, which was cyclocondensed with hydrazine to afford the triazole derivative 58 (Scheme 20) [109, 110].
The cyclocondensation of thiosemicarbazides 59 with 1 under basic conditions afforded the triazole derivatives 60 (Scheme 21) [111, 112].
Isothiourea derivatives 62 were prepared by reacting commercially available S,S-dimethyl-N-cyanodithioiminocarbonate 1 with primary or secondary amines 61; the latter products were transformed into triazoles 63, 64 in 63–89% yields as shown in Scheme 22 [113].
As shown in Scheme 23, the reaction of the primary amino function of dihydropyridine 65 with 1 affords the N-cyano-S-methylisothiourea 66 in good yield. Compound 66 was converted into 3,5-diaminotriazole 67, N-methyl-3,5-diaminotriazole 68 and 3,5-diaminooxadiazole 69 by reaction with hydrazine, methylhydrazine, and hydroxylaminehydrochloride, respectively [114–118].
The reaction of 1 with hydroxylamine hydrochloride 70 in the presence of a base afforded the 5-amino-3-methylthio-1,2,4-oxadiazole 71 (Scheme 24) [40].
The reaction of 1 with oximes 72 afforded oxadiazoles 73 (Scheme 25) [119].
Six-membered heterocycles
Six-membered rings with one heteroatom
The furylpyridine 75 was synthesized by stirring a mixture of [1-(2-furyl)ethylidene]malononitrile 74 and 1 in the presence of potassium carbonate in N,N-dimethyformamide (Scheme 26) [120, 121].
Six-membered rings with two heteroatoms
A mixture of 5-cyanopyrimidine 76 and its isomer 77 was obtained as shown in Scheme 27 [122].
Cycloaddition of 1 with cyanothioacetamide 78 in ethanol afforded pyrimidinium salt 79, which was acidified with aqueous hydrochloric acid to give 5-cyano-4-methylthiopyrimidine-6-thione 80. Alkylation of 80 with allyl bromide yielded allylthiopyrimidine derivative 81 (Scheme 28) [123–125].
The synthesis of the substituted pyrimidines 83 was conveniently performed by reacting 1 with the enaminonitrile 82 under basic conditions (Scheme 29) [126].
The synthesis of a substituted uracil 87 by the reaction of 1 with alkyl cyanoacetates 84 in the presence of potassium carbonate or potassium hydroxide in DMSO proceeds through the intermediaries of 85 and 86, as shown in Scheme 30 [32, 127].
Synthesis of pyrimidinium inner salts 90 was achieved by the reaction of a pyridinium salt 88 with 1 under basic conditions (Scheme 31) [128]. The presumed intermediate product 89 was not isolated.
A facile synthesis of polysubstituted pyrimidines 92 involves the reaction of N1-acetylacetamidrazones 91 with 1 at room temperature in the presence of potassium carbonate. Formation of 92 or its analogues depends on amidrazone and the reaction time (Schemes 32 and 33) [129, 130].
The treatment of 1 with ethyl or methyl cyanoacetate 84 in the presence of sodium ethoxide followed by treatment of the resultant product 85 with hydrochloric acid in ether afforded 2-amino-6H-1,3-oxazin-6-one 93 through intermediary of a 1,3-oxazinium salt 86 (Scheme 34) [86, 131, 132].
Cyclocondensation of 1 with a reagent 94 under basic conditions afforded 1-methyl-4-azathiabenzene-1-oxide 95, the acetylation of which yielded product 96 (Scheme 35) [133].
Six-membered rings with three heteroatoms
The reaction of S-methylisothiourea 97 with 1 in the presence of a base afforded the 2-amino-4,6-dimethylthio-1,3,5-triazine 98 (Scheme 36) [40].
A new metformin derivative 103 was synthesized as shown in Scheme 37. First, the treatment of 1 with N,N-dimethylguanidine sulfate (99) in the presence of potassium carbonate afforded the triazine 100, which subsequently was oxidized with m-chloroperbenzoic acid (m-CPBA) at room temperature to give the sulfoxide 101. Then, treatment of compound 101 with 2-propylaniline in 1,4-dioxane under reflux conditions gave compound 102, which is a direct precursor to the desired product 103 (Scheme 37) [12].
The S-methylisothiourea 104 (Scheme 38) is a derivative of 1. The reaction of 104 with carbon disulfide in methanolic potassium hydroxide yielded the triazine 106 through the intermediary of a potassium salt 105 [40].
Compound 104 was allowed to react with hexafluoroacetone 107 in the presence of pyridine to afford triazine compound 108 via Chapman-type rearrangement (Scheme 39) [134].
The reaction of 1 with amides 109 in the presence of sodium hydride in a mixture of benzene and N,N-dimethylacetamide affords products 110, which can be cyclized in refluxing methanol to 1,3,5-triazin-2(1H)-one derivatives 111 (Scheme 40) [135].
Compound 26, which was prepared from treatment of 1 with 25, was allowed to react with pyrrolidine in refluxing ethanol to yield a pyrrolidine derivative 112. This compound was cyclized to a thiadiazine 113 by treatment with sodium hydride in DMSO at room temperature (Scheme 41) [136, 137].
Six-membered rings with four heteroatoms
The reaction of S,S-dialkyl sulfurdiimides 114 with 1 in refluxing ethanol, affords 1,2,4,6-thiatriazines 116, through cyclization of the intermediate products 115 (Scheme 42) [138–140].
Conclusion
A large series of five- and six-membered heterocycles with diverse biological activities has been synthesized from the highly reactive compound N-cyanodithioiminocarbonate 1.
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Articles in the same Issue
- Frontmatter
- Reviews
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