Germyl ethers

Enol germyl ethers are known to equilibrate slowly with the C-isomers at room temperature. They can be prepared by the reaction of lithium enolates of ketones with chlorotrimethylgermane as a mixture of the O- and C-germyl isomers (e.g. 89). ... 

Enol germyl ethers are expected to be more stable than the corresponding enol stannyl ethers, but more reactive than the enol silyl ethers. A recent study shows that enol germyl ethers derived from a number of ketones e.g. 162) condense with benzaldehyde at -78 to -40 C without the need for a catalyst. However, the yield of the product (163) appears to be improved by the addition of BF.vOEt2. Interestingly, the presence of lithium halide also affects the reaction (Scheme 54). 

Lithiation of the germyl hydride S -3 with BuLi in ether and subsequent protonolysis led to recovered hydride of [a]o — 18.5 (86% retention)2. It is assumed that both steps proceed with predominant retention of configuration. Carboxylation of the lithio derivative afforded the carboxylic acid R-12, also with retention of configuration (Scheme 4). The corresponding methyl ester underwent decarbonylation upon heating to afford the methoxy derivative R-15, which was subsequently reduced with LiAlH4 to the (—)-hydride S-... 

Scheme 12 Perfluoroalkylation of ketones via germyl enol ethers...

Germyl enol ethers react with perfluoroalkyl iodides under Et3B initiation to give a-pcrfluoroalkyl ketones. The intermediate radical adduct decomposes readily via /1-elimination and provides the a-perfluoroalkyl ketone and a trialkylgermanyl radical as a chain carrier (Scheme 12) [32]. 

Using diazomethane as the limiting reagent, silyl- and germyl-substituted ketenes5-7 in certain cases gave cyclopropanones which were isolated as stable compounds.5,6 Transformations of trimethylsilylketene and triethylgermylkelene to the 2- and 3-substituted cyclobutanones was accomplished in 90 and 82% yield, respectively. Mild reaction conditions (— 78 °C) in diethyl ether solutions were employed. 

Germyl or silyl derivatives of pentafluoro-substituted benzenes react in the same manner with boron trifluoride-diethyl ether complex without cleavage of the C — Ge or C — Si bonds to yield the 1-substituted heptafluorocyclohexa-1,4-dienes l.43... 

The DFT study of the 3 + 2-cycloaddition between ketene and TV-silyl-, IV-germyl-, and TV-stannyl-imines shows that the TV-germylimine reaction is a two-step process the TV-stannylimine reaction is a competition between two- and three-step processes whereas the TV-silyl process follows a three-step process44 A new and convenient synthesis of functionalized furans and benzofurans based on 3 + 2-cycloaddition/oxidation has been reported. The cyclization of cyclic 1,3-bis-silyl enol ethers (48) with l-chloro-2,2-dimethoxyethane (49), via a dianion, produced 5,6-bicyclic 2-alkylidenetetrahydrofurans (50), which are readily oxidized with DDQ to 2,3-unsubstituted benzofurans (51) (Scheme 13)45 The Evans bis(oxazoline)-Cu(II) complex catalyses the asymmetric 1,3-dipolar cycloaddition of a -hydroxyenones with nitrones to produce isoxazolidines.46 The... 

The reaction of dimesitylgermyllithium etherate with diethylchloroaluminium gave an etherate of the corresponding germyl-aluminium compound in 66% yield (equation 120)151. 

Finally, the reaction of double germylation, such as formation of Cl3GeCH2CH2GeCl3 from ethylene and the etherate of trichlorogermane, is of great importance. 

An example of double germylation was first discovered in the reaction of tricloroger-mane etherate with allyl chloride, as shown in equation 3076. Product 29 with two GeCl3 groups was obtained together with the product of condensation. 

A surprising example of a double germylation reaction was first found in the aromatic series. Addition of two GeCl3 groups into 9,10-positions of anthracene and 9-methylantracene (MA) proceeds in the absence of ether, but require bubbling of air through the reaction mixture simultaneously with addition of trichlorogermane81. 

The reactions with germyl iodides were carried out at — 78° with dimethyl ether as solvent. To obtain good yields, the dilithium telluride must be free of ammonia and lithium amides2. 

Reaction of methanetellurol with lithium aluminum hydride in diethyl ether caused liberation of hydrogen and formation of lithium tetrakis[methyltelluro]aluminate. This compound was not isolated but reacted with silyl or germyl halides to give silyl or germyl methyl tellurium derivatives4. 

Freshly prepared lithium wire, and selenium and tellurium powders were used as supplied. Germyl fluoride may be prepared from germyl iodide11 and lead(II) fluoride.12 Chlorotrimethylsilane is distilled through traps at -45° (chlorobenzene-liquid N2 slush), -78° (methanol-dry ice slush), and -196° (liquid N2) the fraction retained in the trap at -78° is the desired purified chlorotrimethylsilane. Peroxide-free diethyl ether was distilled in a vacuum system from fresh Li[AlH4] and stored in vacuo. Caution. The use of Li[AlHA] for drying ethers can lead to explosions 3 Commercial dry NH3 (10-15 mL portion) was further dried by condensation onto Na pellets (about 1 g) in an ampul (about 50 mL) held at -78° on the vacuum line. After 30 minutes the dried NH3 was pumped from the ampul and degassed in a trap held at -196° before use. 

It should be noted that tribromogermane forms the product of double germylation Br3GeCH2CH2GeBr3 in its reaction with ethylene even in the absence of ether . 

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