Selenenylation, methoxy

In another simple procedure, deprotonation of methoxy bis(trimethylsilyl)methane with butyl lithium and addition of the resulting anion to aldehydes induces Peterson elimination (Scheme 27). The product methyl enol ethers could be hydrolysed to the parent acyl silanes with hydrochloric acid-THF or could be treated with electrophiles such as M-halosuccinimides to give a-haloacyl silanes105. Alternatively, treatment with phenyl selenenyl chloride, oxidation at selenium and selenoxide elimination afforded a,/3-unsaturated acyl silanes. 

Methoxyselenenylation of alkenes.1 This reaction can be effected by reaction of 1 with Br, in CH2C12 to form a red solid that is considered to be a selenenyl bromide. This intermediate reacts with an alkene in CH,OH to give a methoxy- denenylated alkene. The reaction with styrene gives only the Markovnikov product in a yield of 49% and 49% de. 

The first example of the use of the catalytic one-pot procedure described above, in which the deselenenylation occurs with substitution, is represented by the conversion of vinyl halides into a-alkoxy acetals [116]. This is illustrated in Scheme 38 in the case of -bromostyrene 235. The regioselective methoxy-selenenylation affords the a-bromo selenide 236, which undergoes a rapid solvolysis, through a selenium-stabilized carbocation to produce the selenide 237. Oxidation of this alkyl phenyl selenide with ammonium persulfate produces an oxygen stabilized carbocation, which affords the final product 238, and, at the same time, regenerates the selenenylating agent. 

For research of synthetic opportunities of the developed approach, regio- and stereochemistry of cyclization as model substrates we used alkenes 2-7. It is necessary to note that recently in reaction of 2-pyridineselenenyl bromide analogous selenenyl chloride la with styrene 2 in methanol is received only solvoadduct - l-methoxy-l-phenyl-2-(2-pyridylselanyl)ethane - in quantitative yield [18]. 

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