We describe three different series of experiments which were undertaken to test our hypothesis that during irradiation of phosphonium-iodonium ylides (1a, 1b) an electrophilic carbene is generated. By opposing the assumed intermediate to monosubstituted alkynes, we observed in the case of electron-rich substituents at the triple bond a domination of a 1,3-dipolar cycloaddition of the intermediate with the triple bond to yield furans. In the case of electron poorer substituents, the formation of phosphinolines prevails. A second series of experiments was carried out with mixed ylides in which one phenyl ring at the triarylphosphonium group was replaced by a thienyl group. In this case, we observe only an intramolecular reaction with the thienyl ring to yield the phosphinolines 21-23. In a third test, we replaced in the mixed ylides 1a, 1b the COR group by a CN substituent. This modification leads to phosphinolines only and avoids a 1,3-dipolar cycloaddition.

A photochemical reaction of mixed phosphonium-iodonium ylides with acetylenes yielding lambda(5)-phosphinolines, a rare class of phosphorus heterocycles hardly accessible by other methods, was found. The yields of lambda(5)-phosphinolines vary from 35% to 80%. The structures of two phosphinolines were established by single-crystal X-ray diffraction. The X-ray diffraction and NMR spectra data indicate the superposition of ylidic and aromatic structures for phosphinolines.

The Pd-catalyzed amination of 2,6-dibromopyridine with various linear polyamines and oxapolyamines was studied. In this way polyazamacrocycles 3 containing one pyridine and one polyamine moiety were synthesized using equimolar amounts of starting compounds. Two alternative approaches were elaborated and compared for synthesis of macrocycles 11 comprising two pyridine and two polyamine fragments: via intermediate formation of Nα,Nω-bis(6-halopyridin-2-yl)polyamines 7, 8 or via 2,6-bis(polyamino)-substituted pyridines 10. A series of N-(6-tert-butoxypyridin-2-yl)-substituted polyamines 12 and Nα,Nωbis(6-tert-butoxypyridin-2-yl)-substituted polyamines 13 were obtained by similar procedures, and the possibilities of N,N-dihetarylation of such compounds using 2-bromopyridine and 2-bromo-6-tert-butoxypyridine were studied. The yields of linear and cyclic products were shown to be strongly dependent on the nature of starting polyamines and of the halogen atom.

Polyazamacrocycles containing pyridine moieties have been synthesized through the Pd-catalyzed reaction of 2,6-dihalopyridines with various linear polyamines.The synthesis and the coordination properties of polyazamacrocycles containing an endo pyridine nitrogen atom in the macrocyclic ring have been studied by different groups. [1][2][3][4][5][6][7][8] The presence of the pyridine moiety strongly influences the thermodynamic properties and the complexation kinetics by changing the basicity of the ligand and increasing the conformational rigidity of the macrocycle. Indeed, it has been shown that the basicity of ligands containing pyridine is lower than that of corresponding tetraazacycloalkanes. It has also been observed that the metal complexes of such ligands are usually less stable than those of the corresponding tetraazacycloalkanes, while the latter show slower kinetics of formation. In these macrocycles incorporating pyridine, nitrogen atoms are linked to the aromatic ring via one methylene or methyne group. To our knowledge, there is only one report of a macrocycle containing amine-type N atoms directly linked to the pyridine moiety. 9 This compound has been obtained in 25% overall yield after reduction of the corresponding diamide resulting from the reaction of 2,6-diaminopyridine with the suitable diacyl dichloride under high dilution conditions. Devising a straightforward and general route towards such macrocycles is a great challenge.We have recently shown that Pd-catalyzed amination of various aryl dihalides by linear polyamines is a powerful tool for the synthesis of a wide range of nitrogen and oxygen containing macrocycles. 10 Such ligands containing nitrogen atoms directly bonded to an arene moiety may present original complexing properties and serve as new metal sensors. We wish to report herein the synthesis of a wide range of new polyazamacrocyclic compounds incorporating a pyridine ring by using the Pd-catalyzed reaction of 2,6-dihalopyridines with linear tri-, tetra-, pentaand hexaamines, as well as dioxa-and trioxadiamines. Some examples of catalytic amination of halopyridines involving either palladium 11-14 or nickel complexes have been reported previously. 15 First, we investigated the reaction of 2,6-dibromopyridine 1a with tetraamine 2a, which has been successfully used in previously studied amination reactions. The easily available and versatile catalytic system Pd(dba) 2 /BINAP has been chosen. 16 The reactions were carried in refluxing dioxane, in the presence of 4-8 mol% Pd(dba) 2 , 4.5-12 mol% BINAP and sodium tert-butylate, to yield the desired macrocycle 3a (Scheme 1). Scheme 1The progress of the reaction, monitored by 1 H NMR, showed that 2,6-dibromopyridine was entirely consumed after 4-5 hours (c = 0.02 M). Longer heating (up to 22 h) did not significantly change the reaction mixture composition ratio. 2-Amino-6-tert-butoxypyridine (4a) and 2,6-di-tert-butoxypyridine (6) were formed as side-products, through the compound 5. The formation of 2-bromo-6-tert-butoxypyridine (5)...

Dedicated to Professor Rolf Huisgen on the occasion of his 85th birthdayPd-Catalyzed amination of 3,5-dibromo-and 3,5-dichloropyridine (1a and 1b, resp.) with linear polyamines 2 leads to the formation of a new family of pyridine-containing macrocycles 3 with an −exo×-oriented pyridine Natom (Schemes 1 and 2). The dependence of the macrocycle yield on the nature of the halogen atom, the length of the polyamine chain and C/N atom ratio, and the composition of the catalytic system is studied. The synthesis of mono-and bis(5-halopyridin-3-yl)-substituted polyamines 4, 5, 8, 9, and of 3,5-bis(polyamino)-substituted pyridines 6 is described (Schemes 3 and 4), and the use of these compounds as intermediates on the way to the macrocycles 7, 16, and 18 with larger cavity (−cyclodimers× and −cyclotrimers×) is demonstrated (Schemes 5 ± 10).Introduction. ± In the last 15 years, substantial interest was evoked by the synthesis and coordination properties of different polyazamacrocycles which possess a pyridine moiety in the macrocyclic ring [1 ± 13]. This pyridine fragment strongly influences the thermodynamic properties and the complexation kinetics by increasing the conformational rigidity of the ligand and by changing its basicity. Thus, the basicity was shown to decrease in such macrocycles as compared to corresponding saturated molecules like tetraazacycloalkanes. The metal complexes of the pyridine-containing macrocycles are usually less stable than those of tetraazacycloalkanes while the first demonstrate higher formation rates. In all such macrocycles incorporating pyridine, N-atoms are linked to the aromatic ring via one CH 2 or CH group. To date, only one macrocycle containing Natoms directly linked to the pyridine ring has been reported [14]. This compound was obtained by the reduction of the corresponding diamide formed in the reaction of pyridine-2,6-diamine with diacyl dichloride under high-dilution conditions. Macrocycles of this type containing a 3,5-disubstituted pyridine moiety are yet unknown. In our recent work, we have proposed a simple one-pot approach to polyazamacrocycles with an −endo×-position 1 ) of the pyridine N-atom derived from 2,6-dibromopyridine by using Pd-mediated amination with linear polyamines [15]. Therefore, it is of importance to elaborate a simple way to their isomers with an −exo×-oriented