Selenides reactions with alkyl metals

Reaction of alkyl metals with selenides and functionalized selenides 2.6.2.12 Stabilization of carbanionic centers by selenium-containing moieties... 

Reaction of alkyl metals with selenides and functionalized selenides... 

The presence of a group able to delocalize the charge from the caibanionic center favors the synthesis of the carbanion whatever the method used, whereas substitution of the carbanionic center by alkyl groups disfavors it. Thus, whereas methyl phenyl and dimethyl selenide cannot be metallated wiA LDA at -78 °C or 0 C, phenylseleno and methylseleno acetates and propionates lead, on reaction with the same base at -78 °C, to the corresponding organometallics (Scheme 10). - ... 

The whole process involving the reaction of an a-selenoalkyllithium with a carbonyl compound and further reduction of the C—Se bond in the resulting -hydroxyalkyl selenide leads to an alcohol which can be directly produced from an alkyl metal and the same carbonyl compound (Section 2.6.4.2). This two-step procedure offers, in some cases, interesting advantages due to the larger size of a-selenoalkyl-lithiums, which favors a better stereochemical control (see, for example. Scheme 167 for comparison between the two approaches). °... 

Vinyl sulfides and selenides can be alkylated efficiently at the a-position in a two step-one pot reaction which involves their a-metallation and further reaction of the resulting anion with alkyl halides. 

Furthermore, allenyl phenyl selenides have been prepared by alkylation of 1-lithioallenyl phenyl selenide, itself produc on metallation of phenyl 1-propynyl selenide or of allenyl phenyl selenide - (Scheme 42). 1-Lithioallenyl phenyl selenide has poorer nucleophilic properties than that of a-seleno-allyllithiums, since the reaction of the former with 2-phenyl-1-bromoethane gives predominantly styrene, whereas the latter leads to products of substitution in good yield. ... 

Alkynes can be transformed into alkenylstannanes by reaction with stannyl-cuprates. It is possible to trap the 1,2-dimetallic alkene species with various electrophiles. The analogous vicinal difunctionalization of alkynyl selenides " has also been reported. A route to trisubstituted alkenes from phenylthioacetylene"" starts with cuprate addition, but a 1,2-metal rearrangment is involved. Enamines are obtained from N-ethynyldiphenylamine. The alkenylcopper intermediate is also reactive toward many electrophiles. Silylcupration of functionalized alkynes may lead to cyclic products by virtue of intramolecular alkylation. ... 

In contrast, the analogous diethyl-diselenocarbamates (dsc) have been shown to be poor sources for the deposition of ZnSe or CdSe films. Under similar reaction conditions (10 -10 Torr, 370-420° C) the diethyl dsc precursors give films of the metal selenide heavily contaminated with selenium [108]. However the mixed alkyl dsc complex Eq. 4 have been used successfully to deposit thin films of CdSe or ZnSe [109,110]. 

The a-deprotonation of vinylic aryl selenides is strongly dependent on the substituents [4]. For phenyl vinyl selenide, the reaction was successfully carried out with LDA or KDA at -78°C in THF (Scheme 50, reaction 1). When a alkyl group is present, the use of LDA in THF leads to the abstraction of both vinyl and allyl protons. The a-deprotonation was improved using KDA in THF at -78°C (Scheme 50, reaction 2). With two )9,)9 -alkyl groups, the metalation occurred only at an allylic position (Scheme 50, reaction 3). 

Several B metals, the borderline metal Co, and all metalloid metals can form element-carbon bonds that are stable in water. Metallorganic compounds of A ions and of borderline ions (exception Co) hydrolyze in contact with water. Methylation and alkylation are common reactions in biological systems they may also proceed abiotically and generate methyl- or alkyl-element compounds. Examples include selenide, selenoamino acids, methylarsenic acid (MM A A), and dimethylarsenic acid (DM A A) ... 

---