Selenoxides metallation

This strategy involving a Pummerer dehydration of sulfoxide and/or selenoxide is not applicable for preparation of tellurium analogs. The first diheteropentalene bearing the tellurolo[3,4-c]thiophene framework, e.g. 262, has been generated from 259 using tellurium metal in the presence of sodium iodide in DME. Compound 262 appears to be stable in dilute solution for no more than 1-2 h and adds to DMAD across the 4,6-positions in the tellurophene part. The intermediate 263 loses tellurium and collapses to a l,3,5,6-tetramethoxycarbonylbenzo[c]thiophene derivate 264 (Scheme 51) [81],... 

Synthesis of a-selenovinyl metals (1 -seleno-1-alkenyl metals) by metallation of vinyl selenides 2.6.2.23 Synthesis of a-metalloalkyl selenoxides, selenones and selenonium salts... 

Synthesis of a-Selenoalkyl Metals by Addition of Organometallics to Vinyl Selenides, Vinyl Selenoxides and Vinyl Selenones... 

Among these methods, the metallation reaction is the method of choice for selenides bearing electron-withdrawing groups able to stabilize the carbanionic center. This also applies to selenoxides, selenones and selenonium salts. 

In conclusion, a-selenoalkyllithiums and a-selenoxyalkyl metals are versatile building blocks, readily available, and particularly prone to produce 3-hydroxyalkyl selenides and -hydroxyalkyl selenoxides which, after proper activation, have allowed the selective synthesis of various selenium-free compounds. 

Although unable to metallate selenides, dialkyl amides are sufficiently strong to metallate phenylselenoacetals39,46 51) as well as methyl48,52) and phenyl 46,47,52) selenoorthoesters. They are also able to metallate selenoxides 4 9,11 53 55) and selenones 14). Finally selenoacetals are readily available 4,711,12 S6) from carbonyl compounds and selenols in the presence of a Lewis acid and selenoorthoesters have been prepared from orthoesters, selenols, and boron trifluoride etherate47,48,52). 

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