Ring Expansion of Cyclobutanones to Cyclopentanones via α-Lithioalkyl Aryl Sulfoxides and Selenoxides

Article abstract of DOI:10.1021/jo00381a013

Reaction of α-lithioalkyl 2-chlorophenyl sulfoxides (prepared from the corresponding sulfoxides and LDA) with cyclobutanones affords adducts which undergo ring expansion to cyclopentanones upon treatment with potassium hydride.This reaction only works for cyclobutanones substituted at C2 with at least one phenyl or alkenyl group (type I and type II cyclobutanones).Cyclobutanones substituted at C2 with at least one alkyl group (type III and type IV cyclobutanones) undergo similar ring expansion upon treatment with α-lithioalkylphenyl selenoxides followed by direct thermolysis of the adducts.With both the sulfoxide and selenoxide reagents, the carbon atom inserted into the cyclobutanone can be unsubstituted, monosubstituted, or disubstituted.The ring expansions of 17 different cyclobutanones to 29 different cyclopentanones are presented.