PhSe-SePh

These reactions are compared with those of the equivalent 1-alkenyl HgCl compounds. Some differences are observed, notably that the mercury complexes will react with PhSe—SePh, while the tin complexes undergo no reaction at all. The reactions with ChHg, QHgCl and RHgCl, however, are broadly similar to that shown in reaction 26. 

The ingenious solution was to isomerise the alkene and cyclise it in a single operation using light to catalyse both reactions. Cyclisation of Z-18 should give trans-27 by a conrotatory electrocyclic reaction but the reaction was conducted with diphenyldiselenide PhSe-SePh which oxidised it to the benzene 28 in the reaction mixture. So three steps were combined in one. 

The crystal structures of naphtho[l,8-rz/ -l,2-diselenole 4 and naphtho[l,8-r l-l>2-ditellurole 5 were reported <2004HAC530>. The Se-Se and Te-Te bond lengths are 2.3639(5) and 2.727(3)-2.7348(3) A, respectively, while the same bonds in PhSe-SePh and PhTe-TePh are 2.29 <1952AX458> and 2.712(2) A <1972AXB2438>, respectively. The structure of the tetraselenoanthracene 6 has also been reported <2001HAC287>. 

No other derivatives of the tertiary cation, such as the aUylic alcohol in the last part, can r formed this way because the rearrangement is too fast. The reaction with PhSe-SePh and NaBH a trick to get this allylic alcohol. The true reagent is PhSe , formed by reduction of the Se-Se bcr. It is very nucleophilic and will attack even the tertiary epoxide to give a selenide. Oxidation to rh selenoxide leads to a fast concerted cis elimination. The intermediate selenide is unstable as wel m very smelly and must be oxidized immediately before it decomposes. 

From enolates via selenoxidesA Lithium enolates derived from ketones, lactones, and esters react with PhSe-SePh or with phenylselenyl bromide or chloride (PhSeX) to form a-(phenylseleno)carbonyl compounds. These can be oxidized to the corresponding selenoxides with subsequent 5yn-elimination of benzeneselenic acid to form enones. 

PhSe SePh PhSe SePh PhSe SePh... 

Brief irradiation with UV light through a pyrex filter (to remove short wavelength light) in the presence of diphenyldiselenide (PhSe - SePh) gave the trimethyl ester of 268 by isomerisation to Z-272 and oxidative cyclisation. 

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