Reactions of Lithium Silenolates with Carbonyl Compounds

Abstract

The chemical behavior of lithium silenolates, (Me3Si)2SiC(OLi)R (1a, R = Mes; 1b, R = t-Bu), toward carbonyl compounds was studied. Treatment of lithium silenolates 1a and 1b with benzaldehyde and then with chlorotriethylsilane afforded products derived from the reactions of the lithium silenolates with 2 equiv of benzaldehyde, followed by coupling of the resulting anions with chlorotriethylsilane, in good yields. Treatment of 1a and 1b with mesityl aldehyde under the same conditions proceeded similarly to give the respective adducts in high yields, while the reaction of 1a with acetophenone gave the adduct only in low yield. Similar reactions of 1a and 1b with mesityl methyl ketone, however, afforded no adducts but produced lithium 1-mesitylethenolate and the respective acylbis(trimethylsilyl)silanes.

Synthesis of Stable Dianionic Cyclic Silenolates and Germenolates

“…Very similar 13 C chemical shifts were observed for the carbonyl C atom of the two compounds between δ 266.6 and 280.9 ppm in a typical range for carbonyl groups. Furthermore, 2a,b and 4a,b exhibit only two sharp SiMe 2 resonance lines in the 29 Si NMR, which clearly suggest free rotation around the Si (1) −C (1) bond (Table 3). It was not possible to use THF-d 8 for 2b and 4b because a detectable degradation was found within minutes at room temperature.…”

“…The same reactivity was found by Ohshita and Ishikawa, by Marschner et al, and by our group. 13 − 15 , 23 , 28 , 29 Thus, 2b with an alkyl group attached to the carbonyl moiety reacted with an equimolar amount of tetramethyldichlorodisilane (ClSiMe 2 SiMe 2 Cl) at 0 °C in THF with formation of the acyl bicyclo[2.2.2]octasilane 6 . 6 was obtained in nearly quantitative yield (95% yield).…”

“…Again, the same tendency was reported in the case of acyclic silenolates and silanides by Ohshita, Ottosson, and Marschner earlier. 14 , 15 , 28 , 29 , 32 The methylated silicon derivatives 9a , b and germanium derivatives 10a , b were obtained as cis / trans mixtures. The silicon atoms of 9a , b undergo a significant low-field shift from −70 to 45 ppm (in the case of the acyl-substituted silicon atom) and from −131 to −84 ppm (for the silyl-substituted silicon atom).…”

“…We selected MeI as a carbon-centered electrophile, because it represents a benchmark reagent with numerous examples found in the literature. ,, In the reaction of 2a , b and 4a , b with MeI, the same reactivities in terms of reaction sites were observed. In all cases, alkylation of the negatively charged silicon as well as germanium atoms were found in nearly quantitative yields (Scheme ).…”

“…6 was obtained in nearly quantitative yield (95% yield). The asymmetrically substituted acylsilane 6 exhibits two 29 Si resonance lines for the SiMe 2 The aryl-substituted compound 2a exclusively afforded the Osilylated silene 5 under the same conditions (compare Scheme 3). NMR spectral data of 5 (see the Experimental Section) are also typical for a Brook-type silene.…”