Palladium-catalyzed Suzuki-Miyaura coupling of pyridyl-2-boronic esters with aryl halides using highly active and air-stable phosphine chloride and oxide ligands.

The palladium-catalyzed Suzuki-Miyaura coupling of pyridyl-2-boronic esters provided an efficient approach to useful biaryl building blocks containing a 2-pyridyl moiety. The convenient reaction protocol demonstrates its potentially wide applications in medicinal chemistry.

A persistent P,N-heterocyclic carbene.

Conjugate acids of cyclic (amino)(phosphino)carbenes (P-NHCs) have been prepared, and several different processes have been observed during their deprotonation, which include the formation of a metastable P-NHC, an azomethine ylide, and a bicyclic phosphirane.

Synthesis of phosphaformamidines and phosphaformamidinates.

A large-scale synthetic route to a variety of phosphaformamidines and phosphaformamidinates, a type of derivative that was not accessible by the methods previously known for preparing phosphaamidines and phosphaamidinates, is reported. Thermally stable ethyl N-arylformimidates 1 (ArN=CH(OEt), Ar = 2,4,6-(Me)3Ph or 2,6-(iPr)2Ph) readily reacted with lithium dialkyl- and diarylphosphanides to afford the corresponding N-aryl phosphaformamidines in 80 and 60% yield, respectively, whereas with lithium (aryl)(silyl)phosphanide, the N-aryl-N-silylphosphaformamidine (60% yield) was obtained. Addition of primary lithium arylphosphanides to 1 followed by addition of a stoichiometric amount of nBuLi gave rise to the respective phosphaformamidinates (70-88% yield). Methanolysis of the products afforded the N-aryl-N-hydrogenophosphaformamidines (90-95% yield). The solid-state structure of one of the phosphaformamidinates is also presented.

New synthetic routes to C-amino phosphorus ylides and their subsequent fragmentation into carbenes and phosphines.

Phosphonio-substituted aldiminium, iminium, and imidazolidinium salts are readily prepared by the addition of phosphines to the Alder dimer or by treatment of the corresponding chloroiminium salt with the phosphine/trimethylsilyl triflate adduct generated in situ. Reduction with either potassium metal or tetrakis(dimethylamino)ethylene leads to the corresponding C-amino phosphorus ylides. When basic phosphine fragments are used, the ylides can be isolated; otherwise they fragment into the carbene and phosphine. This method is limited to the preparation of transient carbenes, owing to the unavailability of sterically hindered dications, and consequently of phosphorus ylides with bulky carbon substituents. This difficulty is overcome by the addition of 2,4-di-tert-butyl-ortho-quinone to readily available C-amino phosphaalkenes at low temperature. Provided the phosphorus atom bears either an amino or tert-butyl group, [4+1] cycloaddition occurs, and the resulting ylides fragment into a dioxaphospholane and a spectroscopically observed carbene.