Thallium dichlorocarbene

The conditions involving dichlorocarbene generated from chloroform and thallium ethoxide give the best chemoselectivity, yields and reproducibility (Scheme 162, e Scheme 16S, c Scheme 166, e Scheme 186, b Scheme 188, a Scheme 189, The reactions are usually carried out at... 

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. 

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