Special Issue "Sulfur-Nitrogen Heterocycles"

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Abstract: The 3 2 cycloaddition reaction of 1-(4-phenylphenacyl)-1,10-phenanthrolinium ylide with activated alkynes gave pyrrolo[1,2- 4a][1,10]phenanthrolines 6a-d. The "one pot" synthesis of 6a,b,d from 4, activatedalkenes, Et₃N and tetrakis-pyridine cobalt (II) dichromate (TPCD) is described. Thehelical chirality of pyrrolophenanthrolines 6b-d was put in evidence by NMRspectroscopy.

Abstract: 3-Alkyl-thiazolo[3,2-a]benzimidazole derivatives are obtained in high yieldsvia the corresponding 4-alkyl-N-3-(2-aminophenyl)-thiazoline-2-thiones which are easilyprepared from 1,2-diaminobenzene, CS₂ and halogenoketones. This new route comparesadvantageously with the classical mercaptobenzimidazole routes in term of simplicity,isolated yields and availability of the starting materials.

Abstract: Valence topological charge-transfer (CT) indices are applied to the calculationof dipole moments μ. The μ calculated by algebraic and vector semisums of the CTindices are defined. The model is generalized for molecules with heteroatoms andcorrected for sp³-heteromolecules. The ability of the indices for the description of themolecular charge distribution is established by comparing them with μ of the valence-isoelectronic series of cyclopentadiene, benzene and styrene. Two CT indices, μ_vec(vector semisum of vertex-pair μ) and μ_vecV (valence μ_vec) are proposed. The μ_vecVbehaviour is intermediate between μ_vec and μ_experiment. The correction is produced in thecorrect direction. The best results are obtained for the greatest group. Inclusion of theheteroatom in the π-electron system is beneficial for the description of μ, owing to eitherthe role of additional p and/or d orbitals provided by the heteroatom or the role of stericfactors in the π-electron conjugation. The steric effect is almost constant along the seriesand the dominating effect is electronic. Inclusion of the heteroatom enhances μ, whichcan improve the solubility of the molecule. For heteroatoms in the same group, the ringsize and the degree of ring flattering are inversely proportional to their electronegativity.

Abstract: A series of monosubstituted acetonitriles were treated with disulfur dichloride atroom temperature in CH₂Cl₂ to afford 5-substituted-4-chloro-1,2,3-dithiazolium chlorides 1.Where the 5-substituent was not a good leaving group the chloride salts were converted intothe corresponding perchlorate salts 2 which were sufficiently stable and soluble to provideboth ¹H- and ¹³C-NMR and cyclic voltammetry data. Several of the dithiazolium chlorideswere converted into their corresponding 4-substituted-3-chloro-1,2,5-thiadiazoles 13 ontreatment with aqueous ammonia. Mechanisms for all reactions are proposed.

Abstract: The synthesis, characterization and X-ray crystal structure of 2-(4-chloro-phenyl)-7-methylpyrrolo[1,2-b]pyridazine are reported. The compound crystallizes in thespace group P2₁/c (No.14) with a =3.8568(1), b = 11.0690(3), c = 26.4243(7) å, β =92.777(1)° and Z = 4. Accurate molecular parameters for the novel heterocyclic systemwere obtained from intensity data collected at 113K. The molecule assumes a planarconformation in the crystal and the packing is based on π-π stacking with interplanarspacing 3.400 å, typical of aromatic molecules with potential for displaying usefuloptical properties.

Abstract: A route to methyl pyrrolo[2,3-d][1,2,3]thiadiazole-6-carboxylates as potential plant activators and inducers of systemic acquired resistance (SAR) is reported. A synthetic strategy based on cyclization of the thiadiazole ring system utilizing thionyl chloride via the Hurd-Mori protocol as key step was developed. Success of the ring closure reaction turned out to be highly dependent on the nature of the N-protecting group of the pyrrolidine precursor. While electron donors such as alkyl gave only poor conversion to the required 1,2,3-thiadiazoles, an electron withdrawing substituent such as methyl carbamate gave superior yields.