Although it was expected that this elimination should provide a single isomer from the pure diastereomer 12, a partial E, elimination through a benzyl anion intermediate resulted in the formation of the mixture of two dienes. The conformational analysis of 6A based on MM2* calculations (see Scheme 2) predicts that the dominant conformation (>95%) has a twisted diene moiety and an axial orienration of the alkyne side chain at C(2). Attack of the dienophile from the less hindered convex p-face of the diene can explain the slightly preferential formation of 5 . These calculations also suggest "remote control" of the Diels-Alder reaction of 6A, in which intermediate binding of the dienophile (acetylenedicarboxylate) to the alkynyl group attached to the diene moiety in 6a, would help produce compound 5 as the sole product. Crystal structure data of 14: monoclinic, space group P2,/a, N = 11.888(4), h = 27.454(8). r = 10.509(3) A, p =103.68(2)', V = 3333(2) A3. Z = 4: pca,cd = 1.16 gcm-3; 4705 measured reflections, 2525 classed as observed with I2 3.0u(!). Solution of structure by direct methods (Monte-Carlo MUL-TAN), R = 0.073. Further details of the crystal structure investigation may be

No abstract

[reaction: see text] New air-stable PdCl(2){P(t)Bu(2)(p-R-Ph)}(2) (R = H, NMe(2), CF(3),) complexes represent simple, general, and efficient catalysts for the Suzuki-Miyaura cross-coupling reactions of aryl halides including five-membered heteroaryl halides and heteroatom-substituted six-membered heteroaryl chlorides with a diverse range of arylboronic acids. High product yields (89-99% isolated yields) and turn-over-numbers (10,000 TON) are observed.

The phenyl backbone-derived P,O-ligands 1 and 2 were investigated for their utility as ligands in palladium/ligand-catalyzed Suzuki reactions. The 2-(2'-dicyclohexylphosphinophenyl)-2-methyl-1,3-dioxolane (ligand 1) in combination with Pd(dba)(2) affords an efficient catalyst for general Suzuki reactions of a wide variety of arylboronic acids and aryl chlorides, bromides, and iodides to afford the desired biaryl products in high isolated yields. Arylboronic acids and aryl chlorides containing electron-poor, electron-rich, and ortho substituents participate effectively. In contrast, the structurally related ligand 2-(2'-dicyclohexylphosphinophenyl)-1,3-dioxolane (ligand 2) was found to be less efficient under similar conditions. The reaction of ligand 1 with Pd(dba)(2) affords the complex LPd(dba) (14, L = 1). The NMR spectroscopic and X-ray crystallographic data of complex 14 establish that ligand 1 functions as a P,O-chelating ligand in complex 14. The reaction of ligand 2 (2 equiv) with Pd(dba)(2) and excess 4-(t)()Bu-C(6)H(4)Br or the ligand displacement reaction of {Pd[P(o-tolyl)(3)](4-(t)()Bu-C(6)H(4))(&mgr;-Br)}(2) with ligand 2 affords the bis-phosphine complex L(2)Pd(4-(t)()Bu-C(6)H(4))(Br) (13, L = 2). The NMR spectroscopic data of complex 13 establish that ligand 2 in complex 13 functions as a nonchelating ligand. Thus, the higher efficiency of ligand 1 over ligand 2 in Pd/L-catalyzed Suzuki arylation of aryl chlorides can be ascribed to the ability of ligand 1 to generate and stabilize mono-phosphine P,O-chelating Pd/L intermediates, which appear to be most suitable for Suzuki arylation reactions involving certain substrates and conditions.

The new air-stable PdCl2[PR2(Ph-R')]2 complexes, readily prepared from commercial reagents, exhibit unique efficiency as catalysts for the Suzuki-Miyaura coupling reactions of a variety of heteroatom-substituted heteroaryl chlorides with a diverse range of aryl/heteroaryl boronic acids. The coupling reactions catalyzed by the new complexes exhibit high product yields (88-99%) and high catalyst turnover numbers (up to 10,000 TON).