No abstract

Stereocontrolled palladium(II)-catalyzed intramolecular 1,4-oxidations of dienyl acids and alcohols proceed under mild conditions to give fused delta-lactones and pyrans, respectively, in good yields. The stereo- and regioselectivity was affected by the presence of LiCl and solvent composition (HOAc/acetone). The products obtained were used for further functionalizations using copper(I)-mediated reactions. Stoichiometric reactions of preformed dibutylcyanocuprates with pyrans containing an allylic acetate gave cis- and trans-fused ring systems with high gamma-selectivity and in high yields.

The acetate/acetate-d 3 exchange reaction of the ring-bonded acetate of bis(4-acetoxy-[η 3-(1,2,3)-cyclohexenyl])palladium acetate-d 3 complexes 1a−c was studied in acetic acid solutions using 1H NMR spectroscopy. The reactions followed first-order kinetics in palladium, and the rates were highly affected by the presence of methanesulfonic acid or lithium acetate. The nature of the substituent in the 2-position of the complex was found to have a large impact on the reaction rate. Complexes 1a−c are observed intermediates in the benzoquinone-assisted palladium(II)-catalyzed 1,4-diacetoxylation reaction of 1,3-dienes. Complex 1b was treated with stoichiometric amounts of the enantiomerically pure ligand (S)-(+)-2-(4‘-fluorophenylsulfinyl)-1,4-benzoquinone 4 under conditions where no exchange reaction occurs. Kinetic resolution was observed, implying that the two enantiomers of 1b reacted to trans-1,4-diacetoxy-2-phenyl-2-cyclohexene with different rates. Attempts to demonstrate dynamic kinetic resolution in stoichiometric reactions between 1b and 4 were unsuccessful. The major reason for this is presumably that with lithium acetate the equilibrium reaction between the two enantiomers of 1b is too slow compared to the chiral benzoquinone-induced attack of acetate to give the products. Under very acidic conditions the decomposition of the (π-allyl)palladium complex is faster than benzoquinone-induced product formation. This scenario is in full agreement with our observed rates.

The use of a Co(porphyrin)-amide ligand, , in the palladium(II)-catalyzed 1,4-diacetoxylation of conjugated dienes under O2 results in aerobic oxidation. The catalyst was highly active under O2, and the 1,4-diacetoxylation reaction could also be performed under air.

New Chiral Diamide Ligands Containing Redox-Active Hydroquinone Groups. Synthesis and Results in the Palladium(II)-Catalyzed 1,4-Diacetoxylation of 1,3-Dienes. -Some new chiral diamide ligands are prepared. Among them (IIIa) gives the best results. High regio-and diastereoselectivity is achieved, but the enantioselectivity is moderate. -(VERBOOM, R. C.; PLIETKER, B. J.; BAECKVALL*, J.-E.; J. Organomet. Chem. 687 (2003) 2, 508-517; Dep. Org. Chem., Arrhenius Lab., Univ. Stockholm, S-106 91 Stockholm, Swed.; Eng.) -Jannicke 16-097

Palladium(II)-Catalyzed Intramolecular 1,4-Oxyacyloxylation of Conjugated Dienes. A Stereocontrolled Route to Fused Six-Membered Lactones and Pyrans.-It is found that Pd-catalyzed intramolecular 1,4-oxyacyloxylation of conjugated dienes is a useful method to prepare fused 6-membered lactones and pyrans. The regio-and stereoselectivity can be controlled by the presence or absence of Li salts as well as solvent composition. The resulting products are important synthons which can be transformed into cis-or trans-fused 6-membered systems. In contrast, fused 7-membered lactones cannot be prepared under these conditions and 1,4-oxidative cyclization of dienyl amide analogues is unsuccessful. -(VERBOOM, R. C.; PERSSON, B. A.; BAECKVALL*, J.-E.; J. Org. Chem. 69 (2004) 9, 3102-3111; Dep. Org. Chem., Arrhenius Lab., Univ. Stockholm, S-106 91 Stockholm, Swed.; Eng.) -Jannicke 36-125

Cyclohexane derivatives Q 0040Fast and Mild Palladium(II)-Catalyzed 1,4-Oxidation of 1,3-Dienes via Activation of Molecular Oxygen with a Designed Cobalt(II) Porphyrin. -The chiral center in the ligand does not lead to asymmetric induction in the title reaction. -(VERBOOM, R. C.; SLAGT, V. F.; BAECKVALL*, J.-E.; Chem. Commun. (Cambridge) 2005, 10, 1282-1284; Dep. Org. Chem., Arrhenius Lab., Univ. Stockholm, S-106 91 Stockholm, Swed.; Eng.) -M. Paetzel 30-058