25361-60-8Relevant articles and documents
Dihydroselenapyrans by Cycloaddition of Diaryl Selenoketones
Hock, Regina,Hillenbrand, Stefanie,Erker, Gerhard,Krueger, Carl,Werner, Stefan
, p. 1895 - 1904 (2007/10/02)
The phosphorus ylides Ph3P=CAr1Ar2 5 1=Ph, Ar2=4-CH3C6H4 (c); Ar1=Ar2=Ph (d); 4-ClC6H4 (e); 4-FC6H4 (f); 3-CF3C6H4 (g); Ar1=Ph, Ar2=4-ClC4H4 (h)> were allowed to react with elemental selenium at ca. 75 deg C in toluene in the presence of an excess of 2,3-dimethylbutadiene.The diaryl selenoketones 1 thus generated in situ by means of the "Staudinger chalcogenation" reaction were trapped by the added conjugated diene to give the 2,2-diaryl-3,6-dihydro-4,5-dimethyl-2H-selenapyrans 7 in high yield.Similarly, the ylides 5c-f and 5h were treated with selenium, and the resulting diaryl selenoketones 1 added to 1,3-butadiene to give the corresponding 2,2-diaryl-3,6-dihydro-2H-selenapyrans 8.Selenobenzophenone, synthesized analogously, was employed in a cycloaddition reaction with 2,3-dimethoxybutadiene to yield 3,6-dihydro-4,5-dimethoxy-2,2-diphenyl-2H-selenapyran (9), which was characterized by an X-ray crystal structure analysis.Compound 9 crystallizes in the space group P21/n.In the crystal the dihydro-2H-selenapyran adopts a distorted half-chair conformation. - Key Words: Selenoketones / Selenapyrans, dihydro / Staudinger chalcogenation / Phosphorus ylides / Cycloadddition
