Alkenyl selenide

Generation of a selenoaldehyde, a selenoketone, and telluroaldehydes by [3,3] sig-matropic rearrangement of allyl alkenyl selenides and tellurides [139]... 

Selenals, selones, and tellurals generated in situ via [3,3] sigmatropic rearrangements of allyl alkenyl selenides and tellurides 167 can be trapped by 2,3-dimethyl-l,3-butadiene affording the expected cycloadducts (Equation 68) <1995CL135>. Higher yields were noted in less-hindered cases where the selenium and tellurium aldehyde... 

Related results have been described from pyridyl alkenyl selenides which, contrary to odier aryl alkenyl selenides (see below)," are easily metallated at the vinyl site with LDA (Scheme 48, compare i and j with f and h). The ready deprotonation and stereoselective methylation of these selertides have been ascribed to the presence of the nitrogen atom which can reduce the electron density of the double bond and also chelate with the lithium counterion." "... 

C—SeMe and the C—Cl bonds and often faster than that of the C— Br bond The reduction is highly chemoselective and leads to alcohols usually in almost quantitative yield (Scheme 161, a Scheme 164, a Scheme 168, a and b). In rare cases, however, such as when a ca n-carbon double or triple bond is present in a suitable position, the formation of a five- or six-membered ring takes place by trapping of the radical intermediate (Scheme 118). ° Tin hydride reduction has been advantageously extend (g P-hydroxy-y-alkenyl and -hydroxy-a-alkenyl selenides displayed in Scheme IM (a) and Scheme 168 (a and b) and derived from a-selenoalkyllithiums and enenones, and from 1-seleno-l-alkenyl metals and carbonyl compounds, respectively. 

The case of p-hydroxy-y-alkenyl selenides merits further comments. The rearrangement efficiently takes place using the thallium(I) ethoxide method and the presence of an additional double bond in the reactant does not introduce a serious problem associated with unwanted reaction with the dichlorocarbene intermediate. This is not the case when silver tetrafluoroborate is used. 

Coupling with alkenyl selenides. Stereoselective synthesis of aiylalkenes (6... 

When alkenyl selenides are available, they can be converted to the alkenylstannanes by reaction with BujSnH in the presence of AIBN. ... 

AUylsUanes. Alkenyl selenides are viCjSiCHjMgCl in DME in the presence of i 7HF as solvent gives lower yields. 

AUylsUanes. Alkenyl selenides are converted to allylsilanes on treatment with le,SiCH2MgCl in DME in the presence of (PhjPljNiClj [or (PhjPl PdCl ]. Using ether or 7HF as solvent gives lower yields. 

The a,P-unsaturated esters 12 and 14, spirobislactone 16, and vinylogous lactone 18 are smoothly methylenated by Petasis reagent. Silyl esters 22 and 24 are converted to silyl enol ethers 23 and 25. Carbonate 20 can be methylenated to give ketene acetal 21. Amide 26 and lactams can be methylenated, however the reaction is generally sluggish and the complete separation of Ti species is usually difficult. In a similar manner, thioester 28 and selenoester 30 are converted to alkenyl sulphide 29 and alkenyl selenide 31, respectively. Additionally it has been demonstrated that acyl silanes can be converted to the corresponding alkenyl silanes. 

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