Synthesis, conformation and antiproliferative activity of isothiazoloisoxazole 1,1-dioxides.

Sixteen new isothiazoloisoxazole 1,1-dioxides, one new isothiazolotriazole and one new isothiazolopyrazole have been synthesised by using 1,3-dipolar cycloadditions to isothiazole 1,1-dioxides. One sub-set of these isothiazoloisoxazoles showed low µM activity against a human breast carcinoma cell line, whilst a second sub-set plus the isothiazolotriazole demonstrated an interesting restricted rotation of sterically hindered bridgehead substituents. A thiazete 1,1-dioxide produced from one of the isothiazole 1,1-dioxides underwent conversion into an unknown 1,2,3-oxathiazolin-2-oxide upon treatment with Lewis acids, but was inert towards 1,3-dipoles and cyclopropenones. Six supporting crystal structures are included.

Coordination chemistry of tetra- and tridentate ferrocenyl polyphosphines: an unprecedented [1,1'-heteroannular and 2,3-homoannular]-phosphorus-bonding framework in a metallocene dinuclear coordination complex.

PalladiumII and nickelII halide complexes of the ferrocenyl polyphosphines 1,1',2,3-tetrakis(diphenylphosphino)ferrocene (1), and 1,1',2-tris(diphenylphosphino)-4-tert-butylferrocene (5) were prepared and characterized by multinuclear NMR. The metallo-ligand 1, the palladium [Pd2Cl4(1)] (3b) and nickel [NiCl2(5)] (6) coordination complexes were additionally characterized by X-ray diffraction crystallography. The behavior of 1 toward coordination to nickel and palladium was surprisingly different because the coordination of a second metal center after the initial 1,2-phosphorus-bonding of nickel was markedly difficult. The preference of nickel for 1,2-P coordination on 1,1'-bonding was confirmed by the exclusive formation of 6 from 5. The changes noted between the solid state structure of the ligand 1 and the structure obtained for the dinuclear palladium complex 3b reveal the rotational flexibility of this tetraphosphine. This flexibility is at the origin of the unique framework for a metallocenic dinuclear metal complex in which both coexist a 1,1'-heteroannular chelating P-bonding and a 2,3-homoannular chelating P-bonding with two palladium centers. Some reported specimens of ferrocenyl polyphosphines of constrained geometry have previously revealed that phosphorus lone pair overlap can lead to very intense "through-space" 31P31P nuclear spin-spin coupling constants (JPP) ( J. Am. Chem. Soc. 2004, 126 (35), 11077-11087] in solution phase. In these cases, an internuclear distance between heteroannular phosphorus atoms below 4.9 A, with an adequate orientation of the lone-pairs in the solid state and in solution, was a necessary parameter. The flexibility of the new polyphosphines 1 and 5 does not allow that spatial proximity (internuclear distances between heteroannular phosphorus above 5.2 A in the solid state); accordingly the expected through-space nuclear spin-spin coupling constants were not detected in any of their coordination complexes nor in 1.