Enantiomeric resolution and determination of the absolute configuration of dibenzophosphole 5-oxides

Recent studies of the synthesis, functionalization, optoelectronic properties and applications of dibenzophospholes

The dibenzophospholes, synthesized in the 1950s, have recently gained a greater importance, due to their use in organic electronics and the possibility of designing new π-conjugated, optoelectronic materials that incorporate these heterocycles.

Resolution of P-stereogenic P-heterocycles via the formation of diastereomeric molecular and coordination complexes (a review)

TADDOL derivatives and the Ca²⁺-salts of tartaric acid derivatives were found to be versatile and generally applicable resolving agents for the preparation of the enantiomers of P-stereogenic heterocyclic phosphine oxides and phosphinates.

Cyclopalladation of the Prochiral (Di-tert-butyl)(diphenylmethyl)phosphine: Kinetic Lability of the Corresponding (+)-Phosphapalladacyclic Pd−C Bond and the Reluctance of the Phosphine to Bind in a Monodentate Fashion

The ortho palladation of prochiral (di-tert-butyl)(diphenylmethyl)phosphine proceeded readily to give rise to the dimeric complex, di-mu-chlorobis{[(phenyl)(di-tert-butylphosphino)methyl]phenyl-C2, P}dipalladium(II). The (S,S)-(+)-dimer was subsequently obtained by optical resolution with sodium (S)-prolinate. The absolute configuration of the optically resolved (+)-dimer was concluded from the X-ray diffraction studies of the derivatized O,O-acetylacetonate complex. The availability of the (+)-dimer is crucial to the study of the properties of the Pd-C bond. The phosphapalladacycle Pd-C bond exhibited a remarkable thermodynamic stability. It could not be permanently ruptured to give rise to the eta1-P monodentate even in a refluxing acetone solution containing concentrated hydrochloric acid. Instead, the phosphine was noted to fluctuate between the ring closed and opened states via the reversible Pd-C bond cleavage/formation under this condition. Inevitably, this resulted in the racemization of the five-membered organopalladium ring structure. In contrast, such bond cleavage was not observed at room temperature in the absence of HCl. In fact, the phosphine was observed to readily ortho palladate even under conditions not favorable to cyclopalladation. Indeed, the difficulty of isolating the phosphine as a simple eta1-P monodentate coordination complex was further noted by its lack of reactivity toward the N,N-dimethyl-1-(1'naphthyl)ethylaminate palladacycle mu-chloro dimer. Only by enhancing the Lewis acidity of the palladacycle in the form of the positively charged bis(acetonitrile) complex could the phosphine be encouraged to participate in monodentate eta1-P bonding. Even then, this form of coordination was weak and was only observed by NMR spectroscopy.

Synthesis of multiply 13C-labeled furofuran lignans using 13C-labeled cinnamyl alcohols as building blocks

Plant lignans are currently being widely studied for their potential benefits for human health as their consumption has been correlated with lower risks for developing chronic diseases, such as breast cancer and coronary heart disease. However, studies of some classes of lignans, in particular the furofurans, are hampered by the lack of suitable standards to allow accurate analysis. Herein, we report the syntheses of two racemic (13)C-labeled furofuran lignans [7,8,9-(13)C(3)]medioresinol and [7,8,9-(13)C(3)]sesamin as internal standards for LC-MS analysis. The labeled furofuran lignans were constructed from triply labeled cinnamyl alcohols, using a radical cyclization method.

A General Strategy for the Facile Synthesis of 2,7-Dibromo-9-heterofluorenes

[reaction: see text] A facile, highly efficient, and economical procedure for the preparation of 6,6'-diiodo-4,4'-dibromo-3,3'-dimethoxylbiphenyl has been found. From this compound, a general synthetic strategy for the preparation of 2,7-dibromo-9-heterofluorenes has been developed. Five 2,7-dibromo-9-heterofluorenes have been easily synthesized for the first time according to the procedure presented, opening the door to new classes of inorganic and organometallic conjugated polymeric materials of polyheterofluorenes.

Chiral reagents for the determination of enantiomeric excess and absolute configuration using NMR spectroscopy

Recent advances in the development of chiral derivatizing and solvating agents that facilitate the determination of enantiomeric excess and absolute configuration are reviewed. These include metal-containing species, host-guest systems, donor-acceptor compounds, and liquid crystal discriminating agents. In the aggregate, these reagents can be used to analyze a wide range of compound classes.