Germyl enolate

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]. 

In a series of papers, Itoh and Mikami have reported the high yield, radical a-trifluoro-methylation of ketones using titanium euolates and Mefl/BEts as free radical generator and trifluoromethylating agent . The use of excess Ida and Ti(OPr-/)4 in the preparation of the titanium euolate represeuts the key to the success of the reaction (equation 41). Interest in this reaction stems from the fact that in general, the radical a-trifluoromethylation of ketones via lithium enolates is complicated by the easy defluorination of the a-CFs ketone by the parent enolate . For this reason, less reactive enolates such as silyl or germyl enolates have been initially used instead of lithium enolates" . 

Et3B is an effective tool for halogen atom transfer radical reactions (see also Chap. 1.5). Perfluoroalkyl iodide [29], a-halo nitrile and a-halo ester [30] added to alkenes and alkynes at low temperature. Not only terminal alkenes but also internal alkenes can be employed to furnish iodine atom transfer adducts (Scheme 23). Furthermore, addition of perfluoroalkyl iodide to silyl and germyl enolate provided a-perfluoroalkyl ketones [31]. The reaction would involve the elimination of a tri-... 

O-germylated enolates can be obtained from (Et3M)2Hg (M = Si,Ge) and a-mercuriketones. ... 

Crotonic esters and certain homologues, when converted to their enolates with LDA and treated with stannyl and germyl chlorides, afford the y-metallo derivatives (Table 10)57. In contrast, silylation of these enolates leads to the 0-silyl derivatives. Interestingly, the halostannane derivatives show a strong preference for the (Z) geometry suggestive of a donor-acceptor interaction between the carbonyl oxygen and the electropositive tin atom,... 

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... 

Yamamoto reported that trapping of a hthium enolate, derived from 3-methyl-2-butenoate, wifh MesGeX selectively gave a-germylated derivative (2) (Scheme 11.5) [17]. Trapping with Mf. SifJ or BujSnGl afforded O-silylated product (3) or y-stan-nylated compound (4) respectively. 

This chapter is concerned with the reactions of enol ethers with carbonyl compounds as illustrated in Scheme 1. The enol ethers considered include alkyl, silyl, germyl and stannyl ethers, and to a small extent enol esters. The carbonyl compounds encompass aldehydes, ketones, esters and their functional equivalents. Overall, the reaction depicted in Scheme 1 is similar to the classical aldol and related condensations discussed in Part 1 of this volume. However, in contrast to the basic conditions inherent in... 

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). 

The a-germylated ester (164) reacts with a number of aldehydes and acetals in the presence of Lewis acid to give, regioselectively, the y-products (Scheme 55). In that sense the germanium-masked di-enolate behaves like the siloxy dienes in their regioselection. 

Poly(germaniiim enolate) (186) has been synthesized as shown in Scheme 46.2 0,261 jjj order to form a polymeric material, a,P-unsaturated carbonyl compound was required to react with a germylene in the presence of a lithium catalyst such as LiCl or LiR. It was believed that initial formation of a germyl anion species was achieved by coordination of the Li catalyst to the germylene compound. 

Nucleophilic attack of the germyl anion toward the P carbon of the cyclic ketone formed a Uthium enolate that coordinated to the germylene regenerating a germyl anion. The organogermanium polymer was stable in aqueous solution and had a > 10 T =40°C, and r =221°C. 

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