Pyridinium counter-ions are an old class of compounds in which the N-protonated pyridine can form hydrogen bonds with different anions, such as tetrachloroferrate. In the past, they have been studied as potential single molecule magnets and normally exhibit antiferromagnetic coupling at very low temperatures (< 10 K). Inspired by the last ACA meeting (2016) where the Cahill group demonstrated that 4-bromo-pyridine could be used as linear linker in crystal engineering, we explored the use of pyridinium tetrachlorometalates to coordinate organic ligands such as N-2-pyridylimidoyl-2-pyridylamidine (1) and N-2-pyrimidylimidoyl-2-pyrimidylamidine (2). This resulted in four complexes of 1 and 2 with the metal in a different coordination site than previous reports. Subsequently, pyridinium tetrachloroferrate(III), pyridinium trichloromanganate(II) monohydrate, and dipyridinium tetrachlorocobaltate(II) were reproduced, along with the new compounds dipyridinium tetrachloroferrate(II) (3), 2,6-diaminopyridinium tetrachloromanganate(II) monohydrate (4) and 2,6-diaminopyridinium tetrachlorocobaltate(II) (5). The unit cell of 3 indicates that it is a polymorph of other similar dipyridinium tetrachlorometalates with the refcodes EWAXIJ, PYDMNC and WOHFII. The crystal structure of 5 exhibits strong intermolecular interactions between the cation and the tetrachlocobaltate(II) anions, in which each 2,6-diaminopyridinium cations are coordinating to the tetrachlorocobaltate in a pincer-like fashion consisting of three hydrogen bonds, two in the amino groups and one in the protonated pyridine. The results of these studies will be presented, as well as our efforts towards exploration of these pyridinium counterions in the synthesis of metallic complexes with various organic ligands in the pursuit of metallic clusters.

A variety of N-tert-butanesulfinyl imines were reduced with NaBH4 in THF containing 2% water to provide the corresponding secondary sulfinamides in high yield and diastereoselectivity. By using the same sulfinyl imine starting materials and changing the reductant to L-Selectride, the stereoselectivity could be efficiently reversed to afford the opposite product diastereomer in high yield and selectivity.

The first total asymmetric synthesis of (+)-xestoquinone (1) has been accomplished in 68% ee by a palladium(0)-catalyzed polyene cyclization of naphthyl triflate 44 using (S)-(+)-BINAP as the chiral ligand. Attempts at an asymmetric polyene cyclization using the corresponding naphthyl bromide 41 gave poor enantioselectivities even in the presence of silver salts, thus exemplifying the effect of the coordination state of palladium on the enantioselectivity. A new method for the preparation of 6,7-dihydroisobenzofurans is also described using a [1,2]-Wittig rearrangement on a seven-membered cyclic ether precursor.

[structure: see text] A short five-step synthesis of (+/-)-2,2'-bis(diphenylphosphino)-3, 3'-binaphtho[2,1-b]furan (BINAPFu, 1) starting from 2-naphthoxyacetic acid is reported. The resolution of BINAPFu 1 was possible using our newly developed resolution procedure for phosphines wherein (1S)-camphorsulfonyl azide was used to prepare the bisphosphinimine of BINAPFu via the Staundinger reaction. BINAPFu consistently outperformed BINAP in an asymmetric Heck reaction between 2,3-dihydrofuran and phenyl triflate.

The resolution of a variety of (+/-)-P-stereogenic phosphines is achieved by exploiting the Staudinger reaction of a (+/-)-phosphine with enantiopure (1S,2R)-O-(tert-butyldimethylsilyl)isobornyl-10-sulfonyl azide. The resulting mixtures of diastereomeric phosphinimines are generally separable by fractional crystallization or flash chromatography. Subsequent acid-catalyzed hydrolysis provides the corresponding optically pure phosphine oxides in high yields.

Tipranavir, an important antiviral agent in clinical development for the treatment of HIV, is synthesized in 15 linear steps from readily available starting materials in 25% overall yield by utilizing Pd- and Mo-catalyzed DYKAT reactions to control the quaternary and tertiary stereogenic centers, respectively.

No abstract

(±)-2,2′-Bis(diphenylphosphino)-3,3′-binaphtho[2,1-b]furan (BINAPFu) was synthesized from 2-naphthoxyacetic acid in a five-step sequence in 62% overall yield. A variety of reported resolution procedures for biaryl bisphosphines did not work with (±)-BINAPFu; thus, a new resolution method was developed, involving the Staudinger reaction of the aforementioned racemate of BINAPFu with an enantiopure camphor sulfonyl azide derivative. The resulting diastereomeric phosphinimines were separated by flash chromatography. Subsequent hydrolysis to the corresponding bis-phosphine oxide and trichlorosilane reduction provided enantiopure BINAPFu. The absolute stereochemical configuration of BINAPFu was established by X-ray crystallography. BINAPFu was compared with commercially available 2,2′-bis(diphenylphosphino)-1,1′-binaphthalene (BINAP) in Pd(0)-catalyzed intermolecular Heck reactions. Investigation of the Heck arylation of 2,3-dihydrofuran showed BINAPFu to be more efficacious than BINAP in dioxane at 30 °C. A variety of phosphorus selenides were prepared, and the 1JP-Se coupling constants measured, to obtain a comparative scale of parent phosphine basicity. The phosphorus atoms in BINAPFu were found to be electron deficient when compared with BINAP but slightly more electron rich than trifurylphosphine. Key words: naphthofurans, atropisomers, electron-deficient phosphines, asymmetric Heck reactions, Staudinger reaction.