Pyridinium dicyanomethylide

The Hirshfeld functions give an excellent fit to the density, as illustrated for tetrafluoroterephthalonitrile in chapter 5 (see Fig. 5.12). But, because they are less localized than the spherical harmonic functions, net atomic charges are less well defined. A comparison of the two formalisms has been made in the refinement of pyridinium dicyanomethylide (Baert et al. 1982). While both models fit the data equally well, the Hirshfeld model leads to a much larger value of the molecular dipole moment obtained by summation over the atomic functions using the equations described in chapter 7. The multipole results appear in better agreement with other experimental and theoretical values, which suggests that the latter are preferable when electrostatic properties are to be evaluated directly from the least-squares results. When the evaluation is based on the density predicted by the model, both formalisms should perform well. 

On the other hand, dipole moments obtained with stockholder partitioning tend to be systematically low for pyridinium dicyanomethylide, the value is... 

Irradiation of the pyridinium dicyanomethylide (324) in benzene gives the substituted pyrrole (325), by the postulated route shown (Scheme 242) which originates from the singlet excited ylide. 7,7-Dicyanoazanorcaradiene presumably arises by N—C bond fission in the triplet which produces a dicyanocarbene (of dubious multiplicity) which is trapped by the solvent benzene (67CR(C)(264)1307). Photolysis of the imino-ylide (326) in benzene (equation 200) follows the same pathways initially but the two products result from ring expansions,... 

Cycloaddition reactions of 1,2,3-triphenylcyclopropene with various substituted pyridinium dicyanomethylides gave the corresponding 1,2,3-triphenylindolizines together with cyanotriphenyl-4//-quinolizines, as shown in Scheme 23. The scope of the reaction has been discussed (81JCS(P1)73>. 

Triphenylcyclopropene cycloadds to a variety of pyridinium dicyanomethylides (319) to produce indolizines and quinolizines, eg. ... 

Pyridinium dicyanomethylide reacts with diphenylcyclopropenone to give the 2-quinolizone 33 (Eq. 15).23 Other syntheses of 2-quinolizones start from 2-cyanomethyl- or 2-alkoxycarbonylmethylpyridines, which react with diketene (Eq. 16),24,25 or acetylene dicarboxylate (Eq. 17).17,26 The reaction... 

Perhaps the most stable ylids are pyridinium cyclopentadienylid 86> 121) and pyridinium dicyanomethylid 100>. 

T14687>. The 1,3-dipolar cycloaddition of pyridinium ylides with a,P-unsaturated aldehydes or ketones in the presence of tetrakis-pyridme cobalt dichromate gives 1-acylindolizidines <97SC1395>. Similarly, pyridinium dicyanomethylides react with cyclooctyne to produce indolizidines <97JHC203>. 

Indolizines have been made via carbene addition to 2-vinylpyridine or dipolar addition of pyridinium ylides. 3-substituted indolizines have been obtained in a one step procedure from reaction of chlorocarbenes with 2-vinylpyridine (94CC509). Microwave irradiation has been used in 1,3-dipolar cycloaddition of pyridinium dicyanomethylide with alkynes <94H(38)785>. 

C8D5N3, Pyridinium-1-dicyanomethylide, 46B, 223 C8H5N3, Pyridinium dicyanomethylide, 30B, 131... 

Pyridinium 1-dicyanomethylide neutron diffraction, 2, 116 (80AX(B)1807) Pyridinium hydrochloride X-ray, 2, 110 <62AX427>... 

Pyridinium chloride, N-(4-pyridyl)-hydrochloride quaternization, 2, 175 reactions with amines, 2, 241 Pyridinium chlorochromates as oxidizing agents, 2, 170 reactions, 2, 34 Pyridinium dichromate as oxidizing agent, 2, 170 Pyridinium l-dicyanomethylide... 

Acheson, R.M., and Ansell, P.J., The synthesis of diethyl (p-tolylsulfonyl)ethynylphosphonate and related acetylenes, and their reactions with nucleophiles. Pyridinium-l-dicyanomethylides, and dienes,... 

The reaction of pyridinium iV-dicyanomethylide 223 with ethyl phenylpropiolate 224 (R = C02Et), under solvent-free conditions using MWI afforded a mixture of the two possible regjoisomers 225 and 227. Reaction was performed in a monomode reactor in order to have an accurate control of temperature to prevent the decomposition of 223. The best results (84-87%) were obtained using a molar ratio of ylide dipolarophile 1 1.5 or 1.5 1 and irradiation at 120 W over 25 min at 150°C (Scheme 48). Yields were increased from 61% to 87% when compared with conventional heating. Reactions in the presence of different supports were performed under MWI the best selectivity was obtained using neutral bentonite or silica gel. 

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