Diimino

Thiurets — see 1,2,4-Dithiazolidines, diimino-Thonzylamine antihistamine, 3, 153 Thorpe reaction benzothiophenes from, 4, 876 Thorpe-Ziegler cyclization, 2, 74 Three-membered heterocyclic compounds basicity, 7, 23... 

Tautomeric interconversions of 1,3-diimino-isoindolenine and its nitro and amino derivatives have been studied theoretically by the AMI method (97MI9). 

The relative stability of 2,5-diaminopyrrole- (95) and 2,5-diimino-pyrrolidine-type (96) structures for succimidines has not yet been clarified, although ultraviolet -spectral data indicate that forms of type 97 are probably unimportant. Banfield has discussed... 

Fragmentary ultraviolet spectral data are available for 3-amino-1,2,4-triazole. Early chemical data on 3,5-diamino-2-phenyl-l,2,4-triazole were interpreted on the basis of the diimino structure 201, but ultraviolet spectral evidence was later stated to favor either structure 202 or 203. ... 

An early application of this reaction to the preparation of barbiturates starts by the condensation of the ketone, I21, with ethyl cyanoacetate by Knoevenagel condensation. Alkylation of the product (122) with ethyl bromide by means of sodium ethoxide affords 123. Condensation of this intermediate with guanidine in the presence of sodium ethoxide gives the diimino analog of a barbiturate (124). Hydrolysis affords vinbarbital (111). > ... 

Chemical Name N,N"-bis(4-chlorophenyl)-3,12-diimino-2,4,11,13-tetraazatetradecane-di-imidamide... 

CN 3,3 -[(l,6-dioxo-l,6-hexanediyl)diimino]bis[2,4,6-triiodobenzoic acid] disodium salt... 

The addition of a 2-methyl-2-penten-4-yl radical to the QDI (based on p-phenylene diamines [PPDs] thus producing the corresponding PPD radical) is highly exothermic. The reaction not only stabilizes the relatively unstable alkenyl radical, but also results in the aromatization of the diimino-cylcohexadienyl ring. The enthalpy of reaction for this reaction is calculated (using MOPAC/AMl Hamiltonian ) to be about —40 kcal/mol. 

Reactions of PdCl2(PhCN)2 with (5)- VV,VV -bis[2-(diphenylphosphino)benzylidene]-2,2 diimino-1,1 -binaphthylene and (5,5, )-iV,iV -bis[2-(diphenylphosphino)benzylidene]-1,2-diimino-1,2-diphenyl-ethane give unexpected results, as shown in Scheme 10 593... 

Recent developments in chirality induced by ligands, and in efficient synthetic methods for ligands such as diphosphines, chiral diamines, amino-phosphine-phosphinites, phosphino-oxazolines and diimino-diphosphines, are available in the literature.105-107... 

The oxidation of amidinothioureas by a range of oxidizing agents to give 3,5-diimino derivatives is still one of the most versatile methods for the synthesis of N-linked derivatives (see Section 5.08.9.4). An alternative method which gives symmetrical derivatives is the oxidation of A-arylthioureas to produce Hector s bases which readily isomerize to give 3,5-diamino-l,2,4-thiadiazoles (see Section 5.08.9.2). 

Likewise, suitable starting materials are iminoisoindolines, especially diimino-isoindoline (l-amino-3-iminoisoindolenine), which reacts with a cyanoacetamide NCCH2CONHR5 to afford a mono-condensation product 49. Further reaction with a compound containing an activated methylene group (such as cyanoacetamide derivatives, barbituric acid) yields the desired pigment 47 ... 

As in the case of o-dioxolenes, the diimine derivatives also form tris-complexes. Figure 38 for instance shows the molecular structure of the benzoquinone diimino dication [Osn(bqdi)3]2 +. 50c... 

The condensation of biguanide and cyanamide (which, in its diimino-form, may be regarded as the parent compound of carbodiimides (373)) has apparently not been studied. The patent literature (85,109) describes the manufacture of melamine by heating mixtures of biguanide or guanidine or their salts with cyanamide or dicyandiamide to 140—240°. but since each of these compounds alone yields melamine under these conditions, the course of these reactions is not clear. The only valid example appears to be the condensation of p-chlorophenylcyanamide and p-chlorophenylbiguanide to 2.4-di(p-chlorophenyl)melamine (304). 

A recent review on four-membered heterocycles formed from imino-phosphoranes concentrates on the preparation and the reactivity of 2,4-diimino-l,3-diazetidine and related compounds (93JPR305). As an example, the synthesis via bisiminophosphorane 85 is described in Scheme 42. The bisiminophosphorane has both a heteroaryl and a styryl site. From a mechanistic view, the reaction of the bisiminophosphorane proceeds with aryl isocyanate formation via an aza-Wittig mechanism. Intermediate car-bodiimide formation (86) occurs directly on the iminophosphorane moiety... 

The treatment of thiurets (diimino-l,2,4-dithiazolidines, (297)) with aromatic amines results in ring opening to form thiocarbamylguanidines (298) and sulfur cyclization to 3,5-diamino-1,2,4-thiadiazole derivatives (299) can occur spontaneously or upon oxidation (Scheme 67) <84CHEC-1(6)463 >. 

Amidinothioureas (342) are oxidized by a range of oxidizing agents to give 3,5-diimino derivatives (343) (Equation (54) see also Schemes 51 and 52) <81ijc(B)825, 87JIC675>. 

Isomerization of 5-imino-l,2,4-dithiazolidine-3-thiones (34) into l,2,4-thiadiazolidine-3,5-di-thiones (51) by a Dimroth rearrangement (see Section 4.13.6.1.1) is a reversible process <91JPR107>. The equilibrium position strongly depends on the nature of substituents. When R = R = Me or Pr the equilibrium position is (34) (51) =1 2, with R = R = Et the ratio is 1 9. When R = Ar, R = Aik, the equilibrium is almost wholly shifted to the right. The forward process is usually accelerated by bases, the reverse by acids. When both substituents are Ar no isomerization occurs <91JPR107>. Isomerization of the 3,5-diimino analogue (52) to a monothione isomer (53), accelerated by pyridine, reaches an equilibrium ratio of (52) (53) =1 9 <89BSB879>. 

Diimino-l,2,4-dithiazolidine (103) undergoes Dimroth rearrangement under the influence of P(OEt)3 which presumably coordinates at the sulfur atom <86JOC407>. Reduction by LiAlH4 also appears to involve attack at sulfur <8610C407>. 

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