Dicyano compounds formation

Generally, during hydroboration polymerization of dicyano compounds, the formation of the borazine structures that have a six-membered boron-nitrogen ring (scheme 19a) and dihydroborated end groups (scheme 19b) as a structural defect is unavoidable. The borazine cross-linked structures often cause the gelation, and dehydroboration causes a decrease in molecular weight. 

Reaction of quinazoline, benzoyl chloride, and trimethylsilyl cyanide in a 2 2 1 molar ratio in anhydrous dichloromethane affords l,3-dibenzoyl-2,4-dicyano-l,2,3,4-tetrahydroquinazoline in 25% yield. When the reaction of quinazoline with trimethylsilyl cyanide and benzoyl chloride or a,/ -unsaturated acid chlorides [molar ratio (1 2.2 2.2)] is carried out in the presence of a catalytic amount of anhydrous aluminum trichloride, a more vigorous reaction takes place and the quinazoline di-Reissert compounds 22 are obtained in higher yield. Attempted Reissert compound formation with benzoyl chloride and potassium cyanide using a dichloromethane/water solvent system leads to ring opening (cf. pp 84, 149). 

It is known that hydroboration reaction of cyano groups gives iminoborane species which dimerize to form B-N four-membered ring (cyclodiborazane) in the case of appropriate borane used [16]. When this reaction is used for the bifunctional monomers, formation of polymeric materials consisting of cyclodiborazane units can be expected. Concerning the preparation of poly(cycIodiborazane)s, we have recently reported two new methods, i.e., allylboration polymerization of dicyano compounds with triallylborane [17], and polycondensation between bis(silylimine)s and chlorodialkylboranes [18]. 

Dicyano-substituted triafulvenes react with enamines to produce exclusively the cross-conjugated dicyanomethylene compounds 519, whose formation can be rationalized by a methylene bicyclo(2,l,0)pentane intermediate 51879 296 Since cyclanone enamines 520 and other cyclic enamines 522 react analogously, this C-C-insertion 237) of the triafulvene ring skeleton into the enamine C=C bond represents a versatile ring expansion mode (C + C3), which makes accessible a series of unsaturated medium-ring compounds (521/523) that are otherwise difficult to synthesize. 

The peripheral selenodiazole rings of porphyrazine (169) can be opened upon treatment with H2S with the proposed formation of the octaaminoporphyrazine (184), which was not isolated and instead converted into the tetrakis(pyrazino)porphyrazine (185) (Scheme 34) (171). Other heterocycles have been fused on the periphery of porphyrazines, such as l,3-dithiol-2-thione in order to extend the aromatic core (172). Macrocyclization of 4,5-dicyano-l,3-dithiole-2-thione (186) under Linstead conditions in the presence of magnesium butoxide produced the symmetrically substituted tetrakis(l,3-dithiol-2-thiono)porphyrazine (187) (Scheme 35). Due to the low solubility of porphyrazine 181, a consequence of the planar aromatic molecular structure, a full characterization of this compound could not be accomplished. 

Table 3 presents the experimental enthalpies of formation of polynitrobenzenes and Table 4 presents the calculated additivity values and DSEs for these same compounds. Enthalpy-of-formation values have been determined experimentally for all three dinitrobenzene isomers in the gaseous state. The enthalpy-of-formation difference between the meta and para isomers is indistinguishable from 0. Conventional wisdom suggests that the para isomer should be destabilized relative to the meta because of adjacent positive charges in key ionic or polar resonance structures. Thus it seems that electronic effects due to meta/para dinitro substituent position are small. This small enthalpy-of-formation difference is similar to that for the meta and para dicyano, difluoro and dichloro benzenes, but does not mimic the ca 22 kJ mol 1 difference for the phthalic acids with which the... 

Studies directed toward the synthesis of bicyclomycin have resulted in the discovery of efficient routes to the construction of the 2-oxa-8,10-diazabicyclo[4.2.2]decane system (160). Thus, the monolactim ether (155) with a hydroxypropyl side chain at position 3, on oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ), gave the product (156) in good yield, presumably via an iminium species (Scheme 51). No trace of the spiro compound (157) could be detected in this reaction. The formation of (156) is probably kinetically controlled. Prior protection of the alcohol as a silyl ether, followed by DDQ oxidation, gave the pyrazinone (158) subsequent deprotection and acid treatment gave the thermodynamically preferred spiro compound (159). The method has been extended to the synthesis of (160), having an exocyclic methylene this compound is a key intermediate in the total synthesis of bicyclomycin [88JCS(P1)2585]. 

In contrast to the reactivity of the nitroethylenes, acrylonitrile generally reacts with indoles to form the l-(2-cyanoethyl) derivatives (B-70MI30500,79MI30501), whereas Michael addition at the 3-position requires the catalytic effect of copper(II) salts. The addition-elimination reaction of pyrroles and indoles with l,l-dicyano-2-ethoxyethylene proceeds in low yield (<30%) to give the dicyanovinyl derivatives, which can be converted by standard procedures into the formyl compounds (81H(16)1499). Tetracyanoethylene forms charge transfer complexes with indoles, which collapse to the Michael adduct anions and subsequently eliminate a cyanide ion with the formation of the tricyanovinylindole (B-70MI30500). 

Treatment of aminoazines, in particular, 6-aminouracil 305, with cyclic oc,(3-unsaturated ketones was described in [235]. The authors showed that 1,3-dimethyl-6-aminouracil reacts easily with cyclooct-2-enone 313, cyclonon-2-enone 316 and other cyclic unsaturated carbonyls (cyclododec-2-enone, cycloundec-2-enon, etc.), forming the appropriate tricyclic compounds 314, 317 or analogues (Scheme 3.86). The interaction of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) with compound 314 leads to a rearrangement of the carbon skeleton and formation of another tricyclic structure 315, while in the... 

Structures of type XVIII or XIX as proposed for the diazodicyanomethane complex (Table 12) may also apply to the complexes of diphenyldiazomethane and 9-diazo-fluorene. The formation of the ketenimine complex (45) from the reaction of (CN)2CN2 and Ni(t-BuNC)4 probably occurs via attack of the complexed dicyano-methylene carbene on the isocyanide ligand113 The observation that these complexes112 113 catalyze the formation of ketenimines from isocyanides and diazo compounds, a reaction which does not proceed under same conditions without the transition metal, may be of preparative value 113 ... 

The synthesis of 1,2,5-thiadiazoles from a-diamines was studied as early as 1897 when Michaelis attempted the preparation of the parent compound by reaction of ethylenediamine with sulfur dioxide. The product, however, was bissulfimic acid (28) which readily lost sulfur dioxide to form the betaine (28a). Later Shew reported that 3,4-dicyano-l,2,5-thiadiazole (30) results from the reaction of cis-diaminomaleonitrile (29, HCN tetramer) with thionyl chloride, a reaction which is analogous to 2,1,3-benzothiadiazole formation from o-phenylenediamines. The synthesis of the parent 1,2,5-thiadiazole and some alkyl analogs (32) was accomplished by reaction of salts of... 

The effect of the added electron acceptors and donors is interpreted in terms of triple complex formation via their interaction with the exciplexes formed by the phenanthrenes. In the case of the reaction of 3,10-dicyano-phenanthrene and rranj-anethole, it was shown that these two compounds form an exciplex which is quenched by N,N-diethylaniline forming an... 

This 1,3-dipolar compound does not reveal its dipolar nature until a second glance, for it is 2,2-dimethyl-l,l-dicyanocyclopropane. The double reactivity pattern that is illustrated by the simultaneous production of I and VII, is the result of either its tendency to undergo Sn2 attack with little charge separation in the transition state that leads to compound I, or to become zwitterionic intermediate V (that yields VII), which is effectively stabilized by the powerful electron withdrawing gem-dicyano unit (see Scheme 16.2). That the latter option does not contribute significantly to the reaction progress in nonpolar solvents is inferred from the exclusive formation of I in xylene (46% yield). 

Concomitant formation of l,l-dicyano-2-methoxyspiro[2.5]octane was observed and the compound was isolated in 60 % yield. 

The alkene 363 is photochemically reactive on irradiation in a matrix at low temperature. An analysis of the IR spectrum of the photolysate showed that the ketene 364 and acetaldehyde are formed. Extended irradiation of 363 in argon led to the formation of a new compound identified as l,l-dicyano-2-methyloxirane, produced by the addition of dicyanocarbene, formed by secondary irradiation of the ketene, to acetaldehyde. 

In the synthesis of coumarins by the von Pechmann reaction, a spiro-compound (251) was simultaneously formed from 4-chloro-2-methylphenol (and from 2,3,5-trimethylphenol). A possible mechanism for this reaction involves the formation of the lactone (252), which reacts with another molecule of the phenol. The condensation of the dicyano-ester (253) [obtained from malononitrile and ethyl cyanoacetate] with substituted o-hydroxybenzaldehydes yields substituted coumarinimines, e.g. (254).A series of 4,6,7-substituted coumarins have been prepared and assessed for their suitability in fluorescence labelling of polymers. Esters of the type PhCH CRCOaAr react with AICI3 to give coumarins, which are probably formed via dihydrocoumarins (255) by dearylation. ... 

Reaction of the arylamine 62 with the complex salt 52 in acetonitrile at room temperature afforded complex 64 in 87% yield (Scheme 17) [125]. Subsequent oxidative cyclization, aromatization and demetalation using iodine in pyridine provided carbazole 65 in 71% yield. Heating of compound 65 in chlorobenzene in the presence of the acidic cation exchange resin amberlyst 15 led to ring closure with formation of the furo[3,2-a]carbazole 66. Oxidation of the methyl group at C-3 to a formyl group using 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ)... 

Many jr-deficient azaarrmatic compounds (pyridines, pyrimidines, pyrazines, tri-azines, pteridines, and so on) and especially their quaternary salts have a tendency to add water to give the corresponding o -adducts [1,2,11,114—117,138]. A similar process of reversible pseudobase formation due to the addition of the hydroxide ion to A-aUcylazinium [11], 1,4-diazinium [114, 138], and 1,2,4-triazinium [115-117] cations has been well documented in the literature. For instance, 3-phenyl-5,6-dicyano-l-ethylpyrazinium tetrafluoroborate easily adds water under basic conditions to give the corresponding 2-hydroxy adduct (Scheme 37) [138]. 

Also the radical species are easily formed on treatment of l-ethyl-2,3-dicyano-1,4-diazinium [188, 189] and 1-ethyl-1,2,4-triazinium salts [190] with nucleophiles, as evidenced by dimerization of pyrazinyl radicals into the corresponding dimeric structure (Scheme 63). It is worth noting that the synthetic potential of the intermediate radicals can be used as trapped with compounds bearing C-C double or triple bonds, for instance by reacting with allyl carboranes. The latter reaction is accompanied by the hydrolysis of one cyano group and results in the formation of the corresponding 2,5-diazabicyclo[2,2,2]octenes (Scheme 63) [189]. 

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