o-Hydroxyarylphosphanes: Strategies for Syntheses of Configurationally Stable, Electronically and Sterically Tunable Ambiphiles with Multiple Applications

o-Hydroxyarylphosphanes are fascinating compounds by their multiple-reactivity features, attributed to the ambident hard and soft Lewis- and also Brønstedt acid-base properties, wide tuning opportunities via backbone substituents with ±mesomeric and inductive, at P and in o-position to P and O also steric effects, and in addition, the configurational stability at three-valent phosphorus. Air sensitivity may be overcome by reversible protection with BH3 , but the easy oxidation to P(V)-compounds may also be used. Since the first reports on the title compounds ca. 50 years ago the multiple reactivity has led to versatile applications. This includes various P-E-O and P=C-O heterocycles, a multitude of O-substituted derivatives including acyl derivatives for traceless Staudinger couplings of biomolecules with labels or functional substituents, phosphane-phosphite ligands, which like the o-phosphanylphenols itself form a range of transition metal complexes and catalysts. Also main group metal complexes and (bi)arylphosphonium-organocatalysts are derived. Within this review the various strategies for the access of the starting materials are illuminated, including few hints to selected applications.

Luminescent 1H-1,3-benzazaphospholes

2-R-1H-1,3-Benzazaphospholes (R-BAPs) are an interesting class of σ²P heterocycles containing P[double bond, length as m-dash]C bonds. While closely related 2-R-1,3-benzoxaphospholes (R-BOPs) have been shown to be highly photoluminescent materials depending on specific R substituents, photoluminescence of R-BAPs has been previously limited to an example having a fused carbazole ring system. Here we detail the synthesis and structural characterization of a new R-BAP (3c, R = 2,2'-dithiophene), and compare its photoluminescence against two previously reported R-BAPs (3a, R, R' = Me and 3b, R = 2-thiophene). The significant fluorescence displayed by the thiophene derivatives 3b (φ = 0.53) and 3c (φ = 0.12) stands in contrast to the weakly emissive methyl substituted analogue 3a (φ = 0.08). Comparative computational investigations of 3a-c offer insights into the interplay between structure-function relationships affecting excited state relaxation processes.

Crystal structures of three N-(pyridine-2-carbon-yl)pyridine-2-carboxamides as potential ligands for supra-molecular chemistry

The synthesis and single-crystal X-ray structures of three N-(pyridine-2-carbon-yl)pyridine-2-carboxamide imides, with or without F atoms on the 3-position of the pyridine rings are reported, namely, N-(pyridine-2-carbon-yl)pyridine-2-carboxamide, C12H9N3O2 (1), N-(3-fluoro-pyridine-2-carbon-yl)pyridine-2-carboxamide, C12H8FN3O2 (2), and 3-fluoro-N-(3-fluoro-pyridine-2-carbon-yl)pyridine-2-carboxamide, C12H7F2N3O2 (3). The above-mentioned compounds were synthesized by a mild, general procedure with an excellent yield, providing straightforward access to symmetrical and/or asymmetrical heterocyclic ureas. The crystal structures of 1 and 2 are isomorphous, showing similar packing arrangements, i.e. double layers of parallel (face-to-face) mol-ecules alternating with analogous, but perpendicularly oriented, double layers. In contrast, the crystal structure of 3, containing a fluoro- group at the 3-position of both pyridine rings, shows mol-ecular arrangements in a longitudinal, tubular manner along the c axis, with the aromatic pyridine and carbon-yl/fluorine moieties facing towards each other.

π-Excess-aromatic and non-aromatic 1,3-azaphospholes – impact of annulation and multiple reactivity

Syntheses, properties, structure aspects and reactivity of non- and aromatically carbo- and heterocyclic annulated1H- and3H-1,3-azaphospholes are compared to illuminate the impact of annulation, substituent effects, aromatic stabilization and π-excess at phosphorus of the1H-isomers, to demonstrate the current knowledge and open questions in this field of research.

Selective Synthesis of (Z)-Diazadiphosphafulvalene from 2,2'-bis-Azaphosphindole

The unprecedented 2,2'-bis(azaphosphindole) has been synthesized via a new route. Reaction with NaH afforded a dianion derivative 5, which is easily transformed to alkylated bis(azaphosphindole) or (Z)-P,P,N,N-cisoid diazadiphosphafulvalene. The reaction features good regioselectivity and high steroselectivity. Relatively strong fluorescence is observed with diazadiphosphafulvalenes. The X-ray crystal structure analysis showed that dianion ligand 5 is bonded to two Na atoms in a bridging cis-fashion, which allows the synthesis of diazadiphosphafulvalene in a highly stereoselective approach.

Preparation and biological properties of ring-substituted naphthalene-1-carboxanilides

In this study, a series of twenty-two ring-substituted naphthalene-1-carboxanilides were prepared and characterized. Primary in vitro screening of the synthesized carboxanilides was performed against Mycobacteriumavium subsp. paratuberculosis. N-(2-Methoxyphenyl)naphthalene-1-carboxamide, N-(3-methoxy-phenyl)naphthalene-1-carboxamide, N-(3-methylphenyl)naphthalene-1-carboxamide, N-(4-methylphenyl)naphthalene-1-carboxamide and N-(3-fluorophenyl)naphthalene-1-carboxamide showed against M.avium subsp. paratuberculosis two-fold higher activity than rifampicin and three-fold higher activity than ciprofloxacin. The most effective antimycobacterial compounds demonstrated insignificant toxicity against the human monocytic leukemia THP-1 cell line. The testing of biological activity of the compounds was completed with the study of photosynthetic electron transport (PET) inhibition in isolated spinach (Spinacia oleracea L.) chloroplasts. The PET-inhibiting activity expressed by IC₅₀ value of the most active compound N-[4-(trifluoromethyl)phenyl]naphthalene-1-carboxamide was 59 μmol/L. The structure-activity relationships are discussed.