Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1991-06-03
1993-05-11
Lee, Mary C.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
544 9, 540498, 540554, C07D48704
Patent
active
052102092
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to pyrazolo(1,5-a)benzimidazole couplers.
The pyrazolo(1,5-a)benzimidazole (PBI) couplers are useful as magenta couplers for colour photography.
Although previous synthetic routes for the production of these compounds are known the present invention provides a method for their production using ring closure reactions of benzimidazole derivatives.
According to the present invention there is provided a method for the production of a pyrazolo(1,5-a)benzimidazole of the general formula (A): ##STR2## wherein R is a substituted or unsubstituted alkyl or aryl group, and NR.sub.2, or CN, and developer, which method is characterised by reacting a 2-amino or 2-mercapto substituted benzimidazole to form a triazepinone or a thiadiazino derivative respectively, ring contracting said triazepinone or thiadiazino derivative to give the corresponding pyrazolobenzimidazole product, and subsequently removing the substituents at the -3 or -4 positions to provide a compound of the general formula (A).
In a preferred form of the invention R is a methyl or phenyl group and R.sup.1 to R.sup.4 are all H. In another form of the invention R, R.sup.2 and R.sup.3 are all methyl with R.sup.1 and R.sup.4 respectively being a hydrogen substituent.
In one preferred form of the invention the 2-aminobenzimidazole starting material is formed into a 1,2-4-triazepinone derivative and subsequently subjected to ring contraction of the 7-member ring to the pyrazole form.
In another form of the invention a thiadiazinobenzimidazole derivative is subjected to a ring contraction of the 6-member ring to give the pyrazole form.
Accordingly the alkyl or aryl pyrazolo(1,5-a)benzimidazole derivatives of the present invention may be formed either by means of the mercapto compound (referred to hereinafter as the sulphur extrusion route), or by means of the amino substituted compound (hereinafter referred to as the ring contraction route).
In one generally exemplary exposition of the sulphur extrusion route the starting materials are selected from a 2-mercaptobenzimidazole and an .alpha.-haloketone.
The former compounds are readily available from ortho-phenylene diamines and carbon disulphide.
Accordingly 2-methylpyrazolo(1,5-a)benzimidazole may be produced by reacting 2-mercaptobenzimidazole (1) with a haloketone such as chloroacetone at the sulphur atom to give a corresponding substituted ketone (2). A plurality of different .alpha.-haloketones may be utilized in this reaction depending upon the desired product or reaction conditions.
Thus where a 2-mercaptobenzimidazole is utilized the substituted ketone starting material may be 2-(acetylmethylthio)benzimidazole. If this last product is reacted under alkaline aqueous conditions with hydroxylamine O-sulphonic acid, at for example, room temperature it gives a precipitate of a thiadiazinobenzimidazole derivative (4) in high yield. This last reaction is believed to proceed via the N-amination of the 2-(acetylmethylthio)benzimidazole to give an intermediate product designated (3) which rapidly cyclises with a loss of water to give the desired compound.
The six membered ring including the sulphur atom may be ring contracted by heating with a mixture of acetic acid and toluene for a number of hours; for example 80. The product which may be 4-acetyl-3-acetylthio-2-methylpyrazolo(1,5-a)-benzimidazole (5) may then be desulphurised under reflux in the presence of mineral acid and ethanol to give the desired 2-methylpyrazolobenzimidazole product.
This reaction sequence is shown diagrammatically in scheme 1 below. ##STR3##
The mechanism of the ring contraction of scheme 1 has not yet been fully elucidated. It is thought probable that a mechanism somewhat as shown in scheme 2 below is involved. Without limitation it is believed that the arrangement shown in scheme 2 involves the initial acylation of the imidazole nitrogen followed by ring formation and subsequent cleavage, possibly assisted by the generation of an acetate anion. A similar mechanism could exist whereby the sulph
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Eastman Kodak Company
Kluegel Arthur E.
Lee Mary C.
Miltenberger Lenora A.
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