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COMMUNICATIONSa single diastereorner by chromatography. The sense of asymmetric induction in this cycloaddition is consistent with a Lewis acid catalyzed Diels-Alder reaction on the s-cis ZnBr, complex 8a.In analogy to previous experiments, Diels-Alder adduct 9 was transformed to the corresponding P-ketothioester in 90% yield and smoothly decarboxylated (70 "C, 24 h) to afford ketone 10 in 86% yield without epimerization at the ring fusion. The synthesis was completed by treatment of 10 with Tebbe reagent"81 to afford synthetic a-himachalene (11) (92% yield), whose spectroscopic and analytical data are identical in all respects to literature values ('HNMR, IR, TLC, [a]D).[151The removable auxiliary X = COX, described here should prove useful in enantioselective ketone-based bond constructions. Although the methodology has been highlighted with al-do1 and Diels-Alder reactions, absolute stereochemical control of other transformations such as the Michael reaction should also be possible. Studies extending the scope of these concepts are currently underway. Experimental SectionGeneral one-flask procedure for the decarboxylation of b-ketoimides: A stirred suspension of KH (1.2 mmol) in THF (10 mL) under argon was charged with EtSH (1 3 mmol) and gas evolved. The white suspension was stirred for 1 h before a solution of /I-oxoimide (1 mmol) in THF (10 mL) was added by cannula. The reaction mixture was stirred until the starting material had been consumed. To the reaction mixture was added water (4 mL) and 2,6-lutidine (10 mmol), followed by AgNO, (2.5 mmol). The reaction mixture was protected from light and stirred for two days. The pale yellow suspension was filtered through Celite with ether, and the organic solution was extracted between ether (50 mL) and aqueous CuSO, solution (50 mL). The ether layer was separated, dried over MgSO,, and concentrated in vacuo. Chromatography on silica gel using an appropriate solvent mixture provided pure ketone.

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The lithium and sodium phenolates of 2-[ (dimethylamino)methyl]phenol, la and 2a, 2-[(dimethylamino)methyl]-4,6-dimethylphenol, l b and 2b, and 2,6-bis[(dimethylamino)methyl]-4-methylphenol, IC and 2c, respectively, have been synthesized. The structures of these complexes in solution were studied by variable-temperature lH and l3C NMR spectroscopy and cryoscopic molecular weight measurements. The solid-state structures of complexes IC and 2c derived from 2,6-bis[ (dimethylamino)methyl]-4-methylphenol, were determined by X-ray diffraction. The complexes containing only one ortho-chelating (dimethy1amino)methyl group, i.e. la,b and 2a,b, are soluble in weakly polar solvents, like tetrahydrofuran. Complexes la and l b are tetramers in benzene. These tetramers occur in solution in two isomeric forms, Le. as aggregates with 0 2 and S 4 symmetry. The lithium "pincer-phenolate" containing two ortho-chelating (dimethy1amino)methyl groups (IC) is a trimer in apolar solvents as well as in the solid-state. It is the first example of a phenolate complex with a stable, trinuclear structure. In contrast, the sodium analog (2c) is a dimer in solution and crystallizes as a tetramer with a cubic-likeNa404 core. Crystals of Li3C3&N603, lc,aremonoclinic,spacegroupP21/n,withunit celldimensionsa= 42.381(5)A,b=8.8417(11)&~= 11.1802(10) A, fi = 90.539( 8)", and Z = 4. The structure was refined to R = 0.068 for 4106 reflections and 610 parameters.The trimeric structure contains a Li303-ring which is almost perfectly planar (within 0.05 A), and very short Li-0 and C-0 bond lengths (averages of 1.865( 9) and 1.317(6) A, respectively). As a result of intramolecular amine coordination IC is a "propeller-like" molecule with screw-type chirality. Crystals of Na4C52Hg4N8O4.C6H6, 2c, are monoclinic, space group P2/c, with a = 16.021(2) A, b = 10.275(1) A, c = 24.190(2) A, B = 130.35(1)O, 2 = 2, and final R = 0.064 for 3476 reflections and 400 parameters. This tetramer consists of a double dimer in which the NMe2 groups of one dimer do exclusively coordinate to the sodium atoms of the same dimer.

A general method for the functionalization of Si−Cl terminated carbosilane dendritic molecules via organolithium or organomagnesium reagents is described. Quantitative exchange of the bromine atoms of 4-bromophenyl-functionalized dendrimers affords polylithiated species that are valuable starting materials for further functionalization, e.g., into pyridyl alcohols. The latter were successfully applied as catalyst precursors in a ruthenium-mediated ring-closure metathesis reaction.Among the many potential applications 1 of dendrimers, the immobilization of catalytically active sites at the periphery of these molecules is of current interest. The first example was the successful use of an arylnickel-functionalized carbosilane as a homogeneous catalyst in the Kharasch addition of polyhalogenoalkanes to CdC double bonds. 2 Today, a number of dendritic molecules are known that contain ligand systems at their periphery to which metal atoms may be bound covalently or via heteroatom donor bonds. This topic has been reviewed recently. 3,4 So far, only a few examples of such metallo-dendrimers have been applied as immobilized catalysts. A recent development is the use of metallo-dendrimers as low-conversion catalysts in continuous membrane-reactor processes. An example is the selective hydrovinylation of styrene with an in situ prepared palladium catalyst immobilized on a carbosilane (CS) dendrimer. 5 Similar examples are palladium-catalyzed C-C bond formation reactions using bisphosphine-containing CS-dendrimers 6 or diaminopropyl-type dendrimers. 7 Peripheral functional groups are often connected to the dendrimer core via heteroatom-containing linkers such as † Utrecht University. ‡ Ciba Specialty Chemicals. (1)