Helmut Reinke

Generation and conversion of the transient 1,1-bis(trimethylsilyl)-2-( 2,4,6-triisopropylphenyl)-silene

Abstract Treatment of 2,4,6-triisopropylbenzaldehyde with tris(trimethylsilyl)silylmagnesium bromide (2) gives 2,4,6-triisopropylphenyl-tris(trimethylsilyl)silyl-methanol (3) in approximately 70% yield and E-3,4-bis(2,4,6-triisopropylphenyl)-1,1,2,2-tetrakis(trimethylsilyl)-1,2-disilacyclobutane (5) (15%). 5 is the [2 + 2] head-to-head cyclodimer of the transient 1,1-bis(trimethylsilyl)-2-(2,4,6-triisopropylphenyl)silene (4), formed by trimethylsilanolate elimination according to a Peterson mechanism from the magnesium alkoxide, derived from the alcohol 3. Deprotonation of 3 with McLi at low temperature in ether produces a complex mixture of products, the main constituents being the silene dimer 5 (10%) and bis(trimethylsilyl)-2,4,6-triisopropylbenzyl-trimethylsiloxysilane (10) (60%), which is formed by readdition of the eliminated lithiumtrimethylsilanolate at the SiC bond of 4. The deprotonation of 3 with McMgBr or PhMgBr (activated by LiBr) in THF at room temperature results in the formation of the polysilane (Me3Si)3SiSi(SiMe3)2CH2(2,4,6-C6H2iPr3) (13). Its generation indicates that there exists an equilibrium between the magnesium alkoxide derived from the alcohol 3 on one side, and the magnesium silanide 2 and 2,4,6-triisopropylbenzaldehyde on the other side. Possible pathways of the formation of the compounds mentioned, as well as of further by-products, are discussed. The 1,2-disilacyclobutane 5 is characterized by an X-ray crystal structure analysis.

Structure and UV spectroscopic properties of a novel dendritic oligosilane

The reaction of (R2MeSi)2MeSi/Li (2 )[ R/SiMe3] with [ClMe2Si]2 yields the double-cored dendritic oligosilane [(RMe2Si)2MeSi/SiMe2]2 (4). The structure of 4 was obtained from X-ray diffraction data, which verify a total of 16 silicon atoms in the molecule and a longest chain of 8 silicon atoms. 4 exhibits an absorption maximum in the near UV at 285 nm (o/5.6/ 10 4 ), a wavelength that is significantly longer than that of the linear octasilane Si8Me18 and is the longest observed for structurally well-defined oligosilane dendrimers so far. # 2003 Published by Elsevier B.V.

Synthesis of 6H-indolo[2,3-b]quinoxaline-N-glycosides and their cytotoxic activity against human ceratinocytes (HaCaT)

N-glycosides of 6H-indolo[2,3-b]quinoxalines were prepared and structurally characterized. The synthesis relies on the cyclocondensation of isatine-N-glycosides with 1,2-diaminobenzenes. Some products exhibit weak cytotoxic activity against human ceratinocytes (HaCaT).

Dihydroxyoligosilanes as novel ligands in coordination chemistry—first synthesis of 2,5-dioxa-3,4-disilatitanacyclopentanes

Abstract The reaction of two equivalents of (Me3Si)2RSiK×3THF (1 R=SiMe3, 2 R=Ph) with Cl2MeSiSiMeCl2, followed by hydrolysis in the presence of NH4(NH2COO) leads to the formation of the dihydroxyoligosilanes MeR(HO)SiSi(OH)RMe [4 R=Si(SiMe3)3, 6 R=Si(SiMe3)2Ph] as diastereomeric mixtures. Addition of two equivalents of n-BuLi to the diastereomerically pure ligands (meso)-4/6 and (rac)-4/6, respectively, and subsequent treatment with Cp2TiCl2 yields the (Z) and (E) arranged five-membered rings (MeRSiO)2TiCp2 [7 R=Si(SiMe3)3, 8 R=Si(SiMe3)2Ph], respectively. The crystal structures of the ligand (rac)-6 as well as of the titanacycles (E)-8 and (Z)-7 are reported.

New Trifluoromethyl Substituted 1,2,3-Triazoles Linked toD-Galactose andD-Gulose

The title compounds were synthesized by 1,3-dipolar cycloaddition of 3,3,3-trifluoropropinyl benzene (2) to the azido sugars 2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl azide (1), 6-O-acetyl-4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranosyl azide (6), 6-azido-6-deoxy-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (12), and methyl 6-azido-4-O-cyclohexylcarbamoyl-6-deoxy-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranoside (16), respectively. Because of the dissymmetry of the dipolarophile 2, always two regioisomeric products were obtained, the nucleoside-analogous compounds 3/4 (from 1) and 7/8 (from 6), respectively, and the reversed nucleosides 13/14 (from 12) and 17/18 (from 16), respectively. Protecting group chemistry like transesterification, deacetalation, hydrodechlorination is demonstrated in some cases. Thus, the trichloroethylidene derivatives 7, 8, 17, and 18 were converted into the corresponding ethylidene derivatives (9, 10, 19, 20) by treatment with tributylstannane/AIBN. An X-ray analysis is given for the 1-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-4-trifluoromethyl-5-phenyl-1,2,3-triazole (4) and for the 1-[6-O-acetyl-4-O-cyclohexylcarbamoyl-2,3-O-(2,2,2-trichloroethylidene)-β-D-gulopyranosyl]-4-trifluoromethyl-5-phenyl-1,2,3-triazole (7).

Synthesis of Push-Pull Derivatives of Levoglucosenone as Precursors of Annellated Pyranosides

ABSTRACT 1,6-Anhydro-3-deoxy-4-S-ethyl-4-thio-β-D-erythro-hexopyranos-2-ulose (2) reacted with carbon disulphide and iodomethane to furnish 1,6-anhydro-3-[bis(methylthio)methylene]-3-deoxy-4-S-ethyl-4-thio-β-D-erythro-hexopyranos-2-ulose (3). Treatment of 2 with dimethylformamide dimethyl acetal yielded 1,6-anhydro-3-deoxy-3-(dimethylaminomethylene)-4-S-ethyl-4-thio-β-D-erythro-hexopyranos-2-ulose (4). The reactions of 3 with malononitrile and hydrazine hydrate furnished 1,6-anhydro-3-[bis-(methylthio)methylene]-2-(dicyanomethylene)-2,3-dideoxy-4-S-ethyl-4-thio-β-D-erythro-hexopyranose (7) and (1R,7R,8R)-2,3,5,6(2,4,5,6)-tetradehydro-7-ethylthio-5-methylthio-3,4-diaza-10,11-dioxatricyclo[6.2.1.02,6]undecane (8a,b), respectively.

Reaction of the (Dichloromethyl)oligosilanes R(Me3Si)2Si−CHCl2 (R = Me, Ph, Me3Si) with Organolithium Reagents and the Synthesis of Novel Kinetically Stabilized Silenes

The dichloromethyloligosilanes R1(Me3Si)2Si−CHCl2 (1a,b) (1a: R1 = Me; 1b: R1 = Ph), prepared by treatment of methylbis(trimethylsilyl)silane or phenylbis(trimethylsilyl)silane respectively, with chloroform and potassium tert-butoxide, treated with the organolithium reagents R2Li (R2 = Me, Ph) to produce the intermediate organolithium derivatives R1R22Si−CLi(SiMe3)2 (10). Hydrolysis of 10 during the aqueous workup afforded the [bis(trimethylsilyl)methyl]silanes R1R22Si−CH(SiMe3)2 (2); quenching of the reaction mixture with chlorotrimethylsilane gave the [tris(trimethylsilyl)methyl]silanes R1R22Si−C(SiMe3)3 (11). The formation of 10 is discussed as proceeding through a remarkable series of isomerization processes involving the transient silenes R1R2Si=C(SiMe3)2 (7), which in the presence of an effective excess of R2Li are immediately trapped to give 10. By the use of sterically congested organolithium derivatives, the nucleophilic addition of R2Li to the Si=C bond of 7 can be prevented and kinetically stabilized silenes obtained. Thus, Ph(2,4,6-iPr3C6H2)Si=C(SiMe3)2 (8b) was synthesized by the reaction of 1b with 2,4,6-triisopropylphenyllithium (molar ratio 1:2). Similarly, (Me3Si)(2,4,6-iPr3C6H2)Si=C(SiMe3)2 (8c) and (Me3Si)(2-tBu-4,5,6-Me3C6H)Si=C(SiMe3)2 (9c) were prepared from (dichloromethyl)tris(trimethylsilyl)silane (1c) and 2,4,6-triisopropylphenyllithium or 1c and 2-tert-butyl-4,5,6-trimethylphenyllithium (1:2), respectively, but due to difficulties in the separation of starting material and side products, 8b, 8c, and 9c were obtained in impure form only. Despite the steric congestion, the compounds are reactive and exhibit the usual behavior of silenes. Thus 8b, 8c, and 9c were chemically characterized by the reaction with water to give silanols, by the addition of methanol to give methoxysilanes and by formal [2+2] cycloadditions with benzaldehyde to afford stable 1,2-oxasiletanes. 1-Methyl-1-(2,4,6-triisopropylphenyl)-2,2-bis(trimethylsilyl)silene (8a), produced as intermediate from 1a and 2,4,6-triisopropylphenyllithium (1:2), proved to be unstable in the presence of excess aryllithium compound. Thus, only the addition product Me(2,4,6-iPr3C6H2)2SiCH(SiMe3)2 (14) was isolated (after hydrolysis).

SYNTHESIS OF ANELLATED PYRANOSE DERIVATIVES ON THE BASIS OF LEVOGLUCOSENONE

ABSTRACT 1,6-Anhydro-2-(dicyanomethylene)-2,3-dideoxy-4-S-ethyl-4-thio-β-D-erythro-hexopyranose (1) reacted with tosyl azide or sulfur and triethylamine to furnish the 5-aza-10, 11-dioxatricyclo[6.2.1.02,6]undeca-2(6),3-diene-3-carbonitrile 2 and the 10,11-dioxa-5-thiatricyclo[6.2.1.02,6]undeca-2(6),3-diene-3-carbonitrile 3, respectively. The reactions of 1 with arylisothiocyanates furnished the 11,12-dioxa-5-thiatricyclo[7.2.1.02,7]dodeca-2(7),3-diene-3-carbonitriles 4 and 5. 3 underwent cyclization with triethyl orthoformate and ammonia or hydrazine hydrate to afford the 5,7-diaza-14,15-dioxa-9-thiatetracyclo[10.2.1.02,10.03.8]pentadecatetra(tri)enes 7 and 8, respectively.

Reaktionen von Bis(trimethylsilyl)amino-substituierten Chlorsilanen [(Me3Si)2N]Me2−nPhnSiCl (n=0, 1, 2) mit Lithium—Darstellung von Bis(trimethylsilyl)amino-substituierten Silyllithiumverbindungen und Disilanen

Abstract The bis(trimethylsilyl)amino-substituted chlorosilanes [(Me3Si)2N]Me2−nPhnSiCl (1: n=0, 2: n=1, 3: n=2) were allowed to react with lithium metal in tetrahydrofuran. 1 slowly reacts at room temperature to the homocoupling product {[(Me3Si)2N]Me2Si}2 (4). An equimolar mixture of 1 and Me3SiCl gives 4 and the cross-coupling product [(Me3Si)2N]Me2Si–SiMe3 (5). The reaction of 2 at −78°C leads to formation of bis(trimethylsilyl)aminosilyllithium [(Me3Si)2N]MePhSiLi (6), which reacts with Me3SiCl and 2 resp. to the corresponding disilanes [(Me3Si)2N]MePhSi–SiMe3 (7) and {[(Me3Si)2N]MePhSi}2 (8). 6 undergoes partially self-condensation at −40 and 0°C and the disilanyllithium [(Me3Si)2N]MePhSi–SiMePhLi (9) is formed. 3 reacts rapidly at 0 and −20°C to give the silyllithium [(Me3Si)2N]Ph2SiLi (12). Treatment of 12 with Me3SiCl and 3 resp. affords the disilanes [(Me3Si)2N]Ph2Si–SiMe3 (13) and {[(Me3Si)2N]Ph2Si}2 (14). The disilane R[(Me3Si)2NMeSi–SiMe3 (11) (R=3,4,5,6-tetrakis(trimethylsilyl)cyclohex-1-enyl) is obtained by reaction of a mixture of 2 and Me3SiCl in molar ratio 1:5 with 6 equivalents of lithium in THF. The crystal structure of 11 is reported. Zusammenfassung Die bis(trimethylsilyl)amino-substituierten Chlorsilane [(Me3Si)2N]Me2−nPhnSiCl (1: n=0, 2: n=1, 3: n=2) wurden mit Lithium in Tetrahydrofuran umgesetzt. 1 reagiert langsam bei Raumtemperatur zum Homokupplungsprodukt {[(Me3Si)2N]Me2Si}2 (4). Ein aquimolares Gemisch von 1 und Me3SiCl ergibt neben 4 auch das Kreuzkupplungs-produkt [(Me3Si)2N]Me2Si–SiMe3 (5). Die Reaktion von 2 bei −78°C fuhrt zum Bis(trimethylsilyl)aminosilyllithium [(Me3Si)2N]MePhSiLi (6), bei dessen Umsetzung mit Me3SiCl bzw. 2 die entsprechenden Disilane [(Me3Si)2N]MePhSi–SiMe3 (7) und {[(Me3Si)2N]MePhSi}2 (8) entstehen. Bei −40 und 0°C unterliegt 6 partiell einer Eigenkondensation, und das Disilanyllithium [(Me3Si)2N]MePhSi–SiMePhLi (9) wird gebildet. 3 reagiert bei 0 und −20°C schnell zum Silyllithium [(Me3Si)2N]Ph2SiLi (12). Die Reaktion von 12 mit Me3SiCl bzw. 3 ergibt die entsprechenden Disilane [(Me3Si)2N]Ph2Si–SiMe3 (13) und {[(Me3Si)2N]Ph2Si}2 (14). Bei der Reaktion eines Gemisches von 2 und Me3SiCl im Molverhaltnis 1:5 mit 6 Aquivalen-ten Lithium in THF entsteht das Disilan-R[(Me3Si)2NMeSi–SiMe3 (11) (R=3,4,5,6-Tetrakis(trimethylsilyl)cyclohex-1-enyl). Die Kristallstruktur von 11 ist beschrieben.

THE REACTION OF TRIS(TRIMETHYLSILYL)SILYLLITHIUM WITH DIBENZOSUBERENONE

Tris(trimethylsilyl)silyllithium ( 1 ) reacts with dibenzosuberenone in ether to give, after carbonyl addition of the lithium silanide and lithium trimethylsilanolate elimination according to a modified Peterson mechanism, the transient silene 5 which is trapped by addition of excess 1 at the SiC double bond to afford 2-[5H-dibenzo[a,d]cyclohepten-5-yl]-1,1,1,4,4,4-hexamethyl-2,3,3-tris(trimethylsilyl)-tetrasilan e ( 7 ). When the same reaction is carried out in dimethoxyethane, no silene is generated, but after carbonyl addition of 1 at dibenzosuberenone a 1,3-Si,O-trimethylsilyl migration occurs, producing the lithium silanide 8 which undergoes an intramolecular addition at the 10,11-CC double bond of the dibenzocycloheptatriene system under formation of a bicyclic organolithium derivative which reacts with excess dibenzosuberenone to afford the alcohol 10 . Compounds 7 and 10 were fully characterized by their IR, NMR and MS data, for 10 the results of an X-ray crystal structure analysis are also given.