New Bis(lithiomethyl)silanes: Building Blocks for Organosilanes

Abstract

The first high yield preparation of non n-stabilized bis(lithiomethy1)silanes was performed by the reductive cleavage of C-S bonds with electron transfer reagents. Ris[(phenylthio)-methyllsilanes synthesized by the reaction of dichlorosilanes with [(phenylthio)methyl]lithium were transformed to the corresponding bis(lithiomethy1)silanes 7 by reaction with lithium naphthalenide (LiClJ18) or lithium p,p'-di-tert-butylbiphenylide (LiDBB) as an electron transfer reagent and were IntroductionDilithioalkanes can be classified as l,l-, 1,2-, 1,3-, 1,4-etc. dilithio compounds by the position of the lithio substituents in the alkyl chain. In contrast to the large number of dilithioalkane compounds, only a few examples of 1,3-dilithioalkane compounds have been described"]. The 1,3-dilithio compounds exhibit enormous synthetic potential as bifunctional building blocks, e.g., for the synthesis of cyclobutane derivatives. These important synthetic building blocks are not available mainly due to the lack of synthetic routes. Also the decomposition by p-elimination of LiH (e.g., 1,3-dilithiopropane decomposes at -60°C to allyllitihiurn[*]) prevented their preparation ['].As a part of our systematic studies['.3] on the structural unit "-CR2-El-CRZ-" (El = element of group 14-16, partly with substituents; R = H, alkyl, aryl) we have investigated the synthesis of bis(1ithiomethyl)silanes with the structural unit "LiCH2-SiR2-CH2Li" (SiR2 = El). The silicon atom stabilizes the lithio substituent in a-po~ition [~] and prevents a p-elimination reaction.Alkyllithium compounds can normally be prepared by[']: 1. hydrogen-lithium exchange with lithium or lithium bases; 2. halogen-lithium exchange with lithium or lithium bases; 3. metal-lithium exchange with lithium or lithium bases; 4. reductive addition of lithium or lithium bases; 5. reductive cleavage of C-S bonds with lithium. Potential synthetic routes for the synthesis of 1,3-dilithiated compounds are the metal-lithium exchange and the reductive cleavage of C-S bonds.For the synthesis of the two known bis(lithiomethy1)silanes. the halogen-lithium exchange (for S5]) and the reductive cleavage of C-S bonds with lithium {for 4r61) have been used (see Scheme lm). 2 was obtained only in 30% yield due to the elimination of LiCl after monometallation. The only high-yield preparation by Bickelhauptr61 is for the derivative LiCHPh-SiMez-CHPhLi (4), which is n-stabi-

Generation and Decomposition of a Pentacoordinate Spirobis[1,2-oxasiletanide]

“…Sequential treatment of diphenylbis((phenylthio)methyl)silane, 7 , with lithium naphthalenide (LiNaph), hexafluoroacetone (HFA), and then aqueous NH 4 Cl gave β-hydroxyalkyldiphenyl((phenylthio)methyl)silane 8 , the hydroxyl group of which was protected with methoxymethyl (MOM) or methyl groups to afford 9a or 9b , respectively. Similarly, the reaction of 9a and 9b with HFA yielded 10a and 10b , respectively, the former of which was deprotected to give diphenylbis(β-hydroxyalkyl)silane 11 .…”

Synthesis and Characterization of Lithiated Dendrimers

“…For the synthesis of known bis(lithiomethyl)silanes, a limited number of reports are available in the literature. Recently a report by Strohmann et al described the high-yield synthesis of a series of bis(lithiomethyl)silanes and tetrakis(lithiomethyl)silanes by reductive cleavage of C−S bonds with lithium naphthalenide. Our strategy was to apply the method of Strohmann et al .…”

Tris- and Tetrakis(lithiomethyl)silanes: An Easy Access to New Building Blocks for Organosilicon Compounds

“…Despite the large number of dilithioalkyl compounds, only a few examples of 1,3-dilithioalkyl compounds have been described. , These have great synthetic potential as bifunctional building blocks, e.g., for the synthesis of cyclobutane derivatives, , but were not available, mainly due to the lack of appropriate synthetic routes. Also, their decomposition by β-elimination of LiH (e.g., 1,3-dilithiopropane decomposes at −60 °C to allyllithium) prevented their preparation…”

“…As a part of our systematic studies ,, on the structural unit “ − CR 2 − M − CR 2 − ” [M = element of groups 14−16, partly with substituents (R = H, alkyl, aryl)], we have investigated the synthesis of bis(lithiomethyl)silanes with the structural unit “Li CH 2 − SiR 2 − CH 2 Li” (M = SiR 2 ). The silicon atom stabilizes the lithio substituent in the α-position and prevents the β-elimination reaction…”

“…We succeeded in preparing the first non π-stabilized bis(lithiomethyl)silanes by reductive cleavage of C−S bonds with electron transfer reagents. , Bis(phenylthiomethyl)silanes, synthesized by reaction of dichlorosilanes with (phenylthiomethyl)lithium, were converted to the corresponding bis(lithiomethyl)silanes by reaction with lithium naphthalenide (LiC 10 H 8 ) or lithium p , p ‘-di- tert -butylbiphenylide (LiDBB). These then were derivatized by reaction with chlorostannanes and chlorosilanes.…”