A HIGH YIELDING, REPRODUCIBLE SYNTHESIS OF TRIMETHYLSILYLKETENE
ABSTRACT A two-step sequence for the preparation of trimethylsilylketene, from chloroacetaldehyde diethyl acetal via ethoxyacetylene, has been modified and optimized.
Reversible insertion of carbenes into ruthenium-silicon bonds.
The five-coordinate carbene complexes [Ru{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}Cl(═CHR)] (2, R = Ph; 3, R = SiMe3), analogues of the Grubbs catalyst, were prepared from the dimer [Ru(μ-Cl){κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}]2 (1) and the corresponding diazoalkane N2CHR. The particular structural features that result from the presence of a strongly trans directing silyl group at the pincer ligand of these complexes are discussed on the basis of NMR information and the crystal structure of the vinylidene analogue [Ru{κP,P,Si-Si(Me)(C6H4-2-PiPr2)2}Cl(═C═CHPh)] (4), which was also obtained from 1 and phenylacetylene. The reactions of 3 with reagents such as P(OMe)3, CO, NCMe, and K(acac) illustrate that the first response of these carbene complexes to an increase of the coordination number around ruthenium is the insertion of the carbene ligand into the Ru-Si bond. These reactions also indicate that the insertion process is reversible and allows typical transformations of carbene ligands such as C-H functionalizations via carbene insertion (in the acac ligand) or the formation of ketene from CO. In addition, the reactions of 3 with terminal alkynes such as phenylacetylene or 3,3-dimethyl-1-butyne show that the inserted carbenes can also undergo reactions typical of metal-bound alkyls such as alkyne insertion and C-H reductive elimination.
Organoaluminum-promoted cycloaddition of trialkylsilylketene with aldehydes: A new, stereoselective approach to cis-2-oxetanones and 2(Z)-alkenoic acids
Abstract The exceptionally bulky methylaluminum bis(4-bromo-2,6-di-tert-butylphenoxide) (MABR) can be successfully utilized as a highly efficient Lewis acid for achieving high stereoselectivity in the cycloaddition of trialkylsilylketene with aldehydes. This method serves as a highly effective route to the synthesis of cis-2-oxetanones from saturated aldehydes, and the synthesis of 2(Z)-alkenoic acids from aromatic and α,β-unsaturated aldehydes.