The ring closing olefine metathesis in protic solvents using a new ruthenium benzylidene complex is described.Ring closing metathesis (RCM) has been established as a powerful and efficient synthetic method for carbon-carbon bond formation leading to carbo-and heterocycles. 1 Many useful transformations have been reported for industrial applications as well as for the synthesis of complex molecules. Today, there are several examples of early transition metal complexes reported that are active catalysts for RCM, most of them tend to be very sensitive towards impurities, oxygen, water or functional groups, however. 2,3 It was also shown that not only were many functional groups tolerated but that RCM could be achieved in methanol and water using suitable substrates. 4,5 Moreover, ring closing metathesis has been succesfully carried out in ionic liquids or supercritical CO 2 . 6 Nevertheless, metathesis active ruthenium alkylidenes, at least those bearing phosphine ligands, require sterically bulky and electron rich phosphine ligands (such as PCy 3 ) to provide and maintain favorable catalytic activity. 7 To enhance the solubility of phosphine stabilized metal complexes in polar solvents in general, polarity is carried most likely by the phosphine backbone. 8 We report here the preparation of a modified ruthenium benzylidene complex 2 for ring closing metathesis by using a new class of neutral, electron-rich and polar phosphine represented by 1.Formally replacing one methylene group of the cyclohexyl rings of the PCy 3 ligand by a polar functionality, e.g. a sulfone moiety, will therefore generate a phosphine 1 with significant enhanced polarity when compared to PCy 3 (Scheme 1). Herein, the 4-position was selected for the isoelectronic replacement far apart from the metal ion because we expected the most dramatic influence on the solubilty while only minor changes in the coordination chemistry should take place, since the rather small change in the ligand backbone should not diminish the required electron donor capabilities of the phosphorous as it was observed in charged phosphines that were reported earlier. 4 With 1 having presumably similar electronic properties to PCy 3 , we attempted to generate a derived ruthenium benzylidene 2.For the latter purpose, alcohol 5 appeared to be an attractive precursor that might be functionalized by further reaction to yield the phosphine 1. The synthesis of 5 had been described earlier, although, in our hands following this synthetic pathway yields were found to be very low. 9 Instead, the easily prepared tetrahydrothiopyran 3 9a was first reduced with NaBH 4 to yield the alcohol 4 in 96% yield and subsequently oxidized using 2 equivalents of potassium periodate yielding the sulfone 5 in 98% (Scheme 2).In the following step, we attempted to activate 5 for a nucleophilic coupling with the deprotonated (dicyclohexylphosphino)borane. After treatment of alcohol 5 with 1.1 equivalents trifluoromethanesulfonic anhydride in the presence of pyridine in dichloromethane, 10 the tr...

Synthesis of Pederic Acid and Related Model Studies. -Different investigations and model studies lead to an optimized preparation of the protected pederic acid (I). -(BREITFELDER, S.; SCHUEMACHER, A. C.; ROELLE, T.; KIKUCHI, M.; HOFFMANN*, R. W.; Helv.

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