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 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.

Conjugate acids of cyclic (amino)(phosphino)carbenes (P-NHCs) have been prepared, and several di erent processes have been observed during their deprotonation, which include the formation of a metastable P-NHC, an azomethine ylide, and a bicyclic phosphirane.Following the discovery of a distillable (phosphino)(silyl)carbene in 1988, 1 a variety of stable acyclic and cyclic carbenes have been prepared. 2 With the exception of bis(amino) cyclopropenylidenes, 3 all these carbenes feature at least one amino or phosphino group directly bonded to the electron-deficient center. Surprisingly, although cyclic diaminocarbenes (NHCs) I, 4 cyclic diphosphinocarbenes (PHCs) II, 5 and acyclic (amino)(phosphino)carbenes III have been isolated, 6 cyclic carbenes of type IV have eluded the synthetic skills of investigators (Fig. 1). Cyclic carbenes have found numerous applications as ligands for transitionmetal based catalysts, 7,8 as catalysts on their own rights, 9 and as initiators for polymerization. 10 In contrast, most acyclic carbenes are poor ligands or give fragile complexes with transition metals, 11 probably because of large carbene bond angles (120-1531). 12,13 The only notable exceptions are the (amino)(phosphino)carbenes III, which allow for different coordination modes. 14 Here we report our efforts towards the synthesis of cyclic (amino)-(phosphino) carbenes (P-NHCs), which should feature the advantages of cyclic carbene systems, and the different coordination modes already described for their acyclic analogues.We have recently shown that conjugate acids of cyclic bis(amino)carbenes (NHC,H + s), (amino)(thio)carbenes and (alkyl)(amino)carbenes can be readily prepared by the addition of a compound featuring two leaving groups to 1,3-diaza-allyl-,1,3-azathio-allyl and 1-aza-allyl anions, respectively. 15 By analogy, phosphaformamidinates 1, 16 prepared by deprotonation of the corresponding phosphaformamidines with butyl-lithium in diethyl ether, appeared to be potential starting materials for the desired P-NHC precursors. Indeed, when the lithium phosphaformamidinate 1a was treated with an excess (4-6 eq.) of 1,3-dibromopropane in Et 2 O, the P-substituted phosphaformamidine 2a was obtained as a light yellow oil in 90% yield (Scheme 1). A THF solution of 2a was then heated at 40 1C for 18 h, and after workup, the cyclic salt 3a was isolated as a white powder in 85% yield. The down field 1 H (d, 8.3 ppm, J PH = 6.9 Hz) and 13 C NMR signals (d, 178.4 ppm, J PC = 2.9 Hz) confirmed the iminium structure of 3a. All attempts to deprotonate 3a with a variety of strong bases (LDA, LiTMP, etc.) led to the cyclic alkene 4a, which was isolated in 75% yield. Interestingly monitoring the deprotonation reaction in THF at 60 1C, by multinuclear NMR spectroscopy, showed the disappearance of the starting material 3a, and the clean formation of a new product, tentatively NIH Public Access Author ManuscriptChem Commun (Camb) identified as the cyclic azomethine ylide 5a, 17 instead of the desired P-NHC. Indeed, the 13 C NMR ...

Phosphonio-substituted aldiminium, iminium and imidazolidinium salts are readily prepared in excellent yields by addition of phosphines to Alder's dimer, or by treatment of the corresponding chloro iminium salt with the in situ generated phosphine/trimethylsilyl triflate adduct. A two-electron reduction, using 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 spontaneously undergo a fragmentation into carbene and phosphine. Although the reduction/fragmentation sequence occurs under mild conditions, this method is limited to the preparation of transient carbenes, due to the non-availability of sterically hindered dications, and consequently of phosphorus ylides bearing bulky carbon substituents. To overcome this difficulty, a second novel route to phosphorus ylides has been developed: The addition, at low temperature, of 2,4-di-tert-butyl-ortho-quinone to readily available C-amino phosphaalkenes. Provided the phosphorus atom bears either an amino or tert-butyl group, a [4+1]-cycloaddition occurs, and the resulting ylides spontaneously undergo a fragmentation into a dioxaphospholane and a spectroscopically observed carbene.

Active and Air-Stable Phosphine Chloride and Oxide Ligands. -The Suzuki-Miyaura cross coupling of pyridine-2-boronates (I) with a wide range of (het)aryl halides is efficiently catalyzed by air-and heat-stable Pd-di(tert-butyl)phosphine complexes. The catalytic activity can be fine-tuned by proper choice of base and solvent. -(YANG, D. X.; COLLETTI, S. L.; WU, K.; SONG, M.; LI*, G. Y.; SHEN, H. C.; Org. Lett. 11 (2009) 2, 381-384; CombiPhos Catalysts, Inc., Princeton, NJ 08542, USA; Eng.) -Mischke 24-140