The X-ray crystallographic structures of nine fluorinated N-(pyridin-4-yl)-N′-phenylureas have been determined in order to study the effect of the regiochemistry and degree of fluorination of the phenyl ring on their solid-state organization. The analysis of the data obtained suggests that, in addition to the traditional N-H‚‚‚N and N-H‚‚‚O strong interactions, the less common and weaker F-based intermolecular interactions also play an important role in the organization of the crystal structure of these ureas, which show specific models of crystal packing as a function of the pattern of fluorine substitution. Particularly relevant are the short distances and strongly directional C-H‚‚‚F-C interactions observed in most of these crystal structures.

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The palladium-catalyzed ureidation reaction of 2-chloropyridines can be regioselectively performed in good yield, with both aryl and aliphatic ureas, using xantphos as the ligand, Pd(OAc) 2 as the source of palladium, NaOt-Bu/H 2 O or NaOH/H 2 O as the base, and dioxane as the solvent The pyridinyl ureido moiety constitutes a structural motif common to several classes of ureas of great interest in the pharmacologic, agronomic and new material fields. 1 Much interest has been recently paid to pyridin-2-yl ureas, which due to the particular disposition of their ureido and pyridine groups are able to participate in specific hydrogen bonding patterns that control their physical and biological properties. Recent examples include pyridin-2-yl ureas with anticancer properties, a new class of potent Cdk4 inhibitors, 2 strong receptors for cytosine, with potential use as DNA binders, 3 a new type of low molecularweight gelators, with great potential for functional materials, 4 and pyridin-2-yl-based photodegradable polymers, potentially useful in the field of micro/nanolithography. 5In general, conventional procedures for the preparation of pyridinyl ureas involve the use of toxic and troublesome reagents such as isocyanates, phosgene or CO 2 . [2][3][4][5]6 In spite of the large amount of research work that has been done on the palladium-catalyzed C-N bond forming reactions of aryl/heteroaryl systems (e.g. amine, 7 amide, 8 imine, 9 carbamate, 10 lactam, 11 sulphonamide, 8 and sulfoximines 12 arylations have been described), only a few examples of palladium-catalyzed arylation of ureas have been reported recently. These include the cross-coupling of urea and phenylurea with activated 13 and unactivated 14 aryl bromides and iodides, the coupling of an aryl bromide with cyclic ureas, 8 and some intramolecular palladium-catalyzed arylation of ureas. 15 To the best of our knowledge, the analogous cross-coupling reaction of heteroaryl halides, and in particular of the generally less reactive chlorides, has not been explored. 16 In relation to our interest in the preparation of pyridinyl ureas, 17 we have investigated the viability of the palladium-catalyzed coupling of readily available chloropyridines with several types of ureas. We show that 2-chloropyridines can react efficiently with both aryl and alkyl ureas, allowing the preparation of both N-phenyland N-alkyl-N¢-pyridin-2-yl ureas in good to excellent yields. 18 Initially, we examined the cross-coupling of 2-chloropyridine (1a) with phenylurea (2) under the conditions previously described by Beletskaya 13,14 for the related coupling of aryl bromides with the same urea (Table 1, entry 1). Under these conditions the reaction took place smoothly, to give a 90% of conversion after 3 hours, affording the expected N-phenyl-N¢-(pyridin-2-yl)urea (3a) in relatively good isolated yield (78%). Trace amounts of aniline (4), N,N¢-diphenylurea (5), 1,5-diphenylbiuret (6) 19 and N-phenyl-N¢-(pyridin-2-yl)amine (7a) 20 were observed as side-products (Scheme 1), the amounts of which s...

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Seventeen phenyl-fluorinated analogues of thidiazuron [N-phenyl-N'-(1,2,3-thiadiazol-5-yl)urea, TDZ] have been prepared and characterized. The effects of each fluorinated urea on growth and quality of kiwifruits (Actinidia deliciosa) were evaluated by comparison with untreated (control) and TDZ-treated fruits. The results obtained showed a clear dependence of the growth-promoting activity of these fluorinated ureas on the pattern and degree of fluorine substitution in the phenyl ring. The most effective for promoting fruit growth was N-(2,3,5,6-tetrafluorophenyl)-N'-(1',2',3'-thiadiazol-5'-yl)urea at 25 ppm (at harvest, treated fruits were 58% heavier than untreated ones) followed by N-(3,5-difluorophenyl)-N'-(1',2',3'-thiadiazol-5'-yl)urea at 10 ppm (50%). Comparatively, TDZ-treated fruits were 31% (10 ppm) and 38% (25 ppm) heavier than untreated ones. The results also indicate that the effects of the more active phenyl-fluorinated ureas on some standard quality parameters of fruits, for example, percent of fruit dry matter content, soluble solids contents, total titratable acids, shape, and internal structure, are similar to those of TDZ. Quantitative structure-activity relationships have been derived for the fruit growth promoting activity of the phenyl-fluorinated analogues of TDZ.

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