Substituted Heterocycles

Boron-substituted heteroaromatic compounds 89AHC(46)143. Dithiocarboxyl esters 88SR(8)155. 

Fluorinated heterocycles 88MI2 90UK149, 90YGK16. Heteroaromatic sulfoxides and sulfones 90AHC(48)1. 

Schiff bases—heterocyclic derivatives 89MI24, 90MI24. Selenoaldehydes—heterocyclic derivatives 88YGK1149. Sulfenamides 89CRV689. 

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AntiviralAg ents. Triduridine [70-00-8] is a triduoromethyl substituted heterocyclic antiviral agent. 

There is a large variety of chloro or fluoro substituted heterocyclic rings which undergo X displacement by cell-0. Vinyl sulfones are usually generated under alkaline conditions from P-sulfatoethjisulfones,... 

Vertical Ionization Energies (eV) of ttj and ir2 Molecular Orbitals of 2-Substituted Heterocycles... 

An appreciable amount of information concerning the conformational preferences of substituted heterocycles has accrued, largely through dipole moment and NMR studies. However, the earliest appreciation of this topic apparently arose out of the extension of studies of restricted rotation in biphenyls to heterocyclic analogues. 

Semicarbazide hydrochloride [705] and amidrazones [106] react with trifluo-ropyruvates to give six-membered heterocycles A variety of trifliioromethyl substituted heterocyclic systems is available, starting from the hydrate of trifluoropy-ruvicacid, a versatile 1,2-bielectrophihc building block (reaction type 2, equation 10) [107] (equation 24). 

As previously described, the Gould-Jacobs reaction has been applied to heterocycles fused to anilines, and to some amino-substituted heterocycles. Selectivity of N- and C-cyclization of 2-aminopyridino-methylene malonates has been mentioned (51 and 56). The normal mode of cyclization of 2-aminopyridino-methylene malonates is on the nitrogen to form a pyridopyrimidine. If an electron-donating group (EDG) is in the 6-... 

The methods outlined, of course, are readily applicable to a wide variety of substituted heterocycles like the carboxyl, hydroxy and mercapto derivatives of pyridines, pyridine 1-oxides, pyrroles, etc. The application to amines and to diaza compounds such as pyrimidine, where the two centers are basic, is obvious except that now 23 takes the role of the neutral compound, 21 and 22 the roles of the tautomeric first conjugate bases, and 20 the role of the second conjugate base. Extensions to molecules with more than two acidic or basic centers, such as aminonicotinic acid, pyrimidinecarboxylic acids, etc., are obvious although they tend to become algebraically cumbersome, involving (for three centers) three measurable Kg s, four Ay s, and fifteen ideal dissociation constants (A ), a total of twenty-two constants of which seven are independent. 

Nitro- and nitroso-substituted heterocycles and related compounds 99JCS(P1)749. 

Methods for synthesis of a,(3-unsaturated trifluoromethyl ketones and their use in the synthesis of trifluoromethyl-substituted heterocycles 99UK483. 

It has been shown that cross-coupling reactions constitute a very mild method to introduce different alkyl and aryl groups to the most active C-3 position of the pyrazinone ring [26]. The broadly functionahzed 2-azadiene system of the title compounds was studied in cycloaddition reactions with various electron-reach and electron-poor dienophiles to provide highly substituted heterocycles [24]. 

The reaction of tetraalkyldistibines with group 13-trialkyls now offers an alternative synthetic pathway for the synthesis of completely alkyl-substituted heterocycles. The first step of the reaction consists of a formation of a 1 1 or... 

Reactions of tetraalkyldistibines and -dibismuthines with trialkylalanes and -gallanes yield bisadducts of the type [R3M]2[E2R4]. These compounds are stable in the solid state, while they easily undergo consecutive reactions in solution. Completely alkyl-substituted heterocycles [R2MER x are formed under cleavage of the Sb—Sb bond, as was demonstrated for two Ga—Sb heterocycles. 

The cycloaddition between a nitrilimine 319 and an aroyl substituted heterocyclic ketene aminal 318 has been found to be stepwise, involving an initial nucleophilic addition of 318 to 319 followed by intramolecular cyclocondensation of the intermediate 320 providing fully substituted pyrazole 321 (Eq. 36) [92]. When Ar was the 2,4-dinitrophenyl group, the intermediate 320 was isolable and required forcing conditions (xylene, reflux, 10 h) to undergo cyclization ... 

The first examples of NHC-Pd complexes applied to the Sonogashira reaction were reported to show a limited scope in the coupling of aryl iodides and activated aryl bromides with acetylene [23,33,52]. However, the use of A-carbamoyl-substituted heterocyclic carbene Pd(ll) complexes expanded the use to alkyl-acetylenes and deactivated aryl iodides and bromides [124] (Scheme 6.40). 

Au( N) CI3 adducts are readily obtained by reaction of AU2CI6 or [ AuCU] with a variety of substituted heterocyclic ligands including 2-phenylpyridine [9], 2-benzylpyridines [10],... 

A variety of gold(III) complexes of carboxamido substituted heterocyclic ligands are obtained by reaction of [AuCh] with the appropriate ligands, these include [Au (N,N )Cl2j (HN,N =picolinamide) (IS) [70], [Au(N,N, N")Cl]Cl [N,N H,N" = N-(8-quinolyl)pyridine-2-carboxamide (16), N-(8-quinolyl)glycine-2-carboxamide (17) or N-(8-quinolyl)-L-alanine-2-carboxamide (18)] [71] (Figure 2.11). 

Figure 2.11 Complexes of carboxamido substituted heterocyclic ligands.

Many amino- and hydroxy-substituted heterocycles have reasonably low oxidation potentials and, as such, can act as lipid-peroxidation inhibitors. We have already discussed triaminopyrimidine examples (tirilazad and U78517) and several ascorbic-acid analogues. This section discusses a few more examples. 

For the purpose of polymer/additive analysis most applications refer to vulcanisate analysis. Weber [370] has determined various vulcanisation accelerators (Vulkazit Thiuram/Pextra N/Merkapto/AZ/DM) in rubbers using PC. Similarly, Zijp [371] has described application of PC for identification of various vulcanisation accelerator classes (guanidines, dithiocarbaminates, thiuramsulfides, mercapto-substituted heterocyclic compounds, thioureas, etc.). The same author has also... 

Benzannulated NHPs are straightforwardly accessible from AUV-disubsti luted o-phenylenediamines either via base-induced condensation with substituted dichlorophosphines [25] or PC13 [26], or via transamination with tris(dialkylamino) phosphines [13, 14, 27], respectively. An analogous NH-substituted derivative was obtained in low yield via transamination of o-phcnylcncdiaminc with ethoxy-bis(diethylamino)phosphine [28], and condensation of o-phenylenediamine with excess tris(diethylamino)phosphine furnished a l,3-bis(phosphino)-substituted heterocycle [29], Intermediates with one or two NH functions were detectable by spectroscopy but could not be isolated in pure form under these conditions. However, 2-chloro-benzo-l,3,2-diazaphospholene and the corresponding 1-phenyl derivative were prepared in acceptable yield via condensation of PC13 with o-phenylenediamine under microwave irradiation [30], or with A-phenyl-o-phenylenediamine under reflux [27], respectively, in the absence of additional base. The formation of tetrameric benzo-NHPs during transamination of A-alkyl-o-phenylenediamines with P(NMe2)3 has already been mentioned (cf. the section entitled 1,3,2-Diazaphospholes and 1,3,2-Diazaphospholides ). 

Substitution of P-substituents other than halogens has been reported for P-ethoxy-l,3,2-diazaphospholene and l,3,2-diazaphospholene-2-oxide which react with trichlorosilane to yield the corresponding P-chloro-substituted heterocycles [49,50]. This reaction reflects a typical behavior of phosphine derivatives undergoing halogen replacement similar to the previously discussed transformations. 

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