Intramolecular ketyl-olefin reductive

In order to effect the overall ring contraction, two complete reaction sequences are necessary. These include a reductive dealkoxyhalogenation to give the ring-opened hex-5-enal followed by an intramolecular ketyl-olefin reductive coupling, to afford the ring contracted organosamarium intermediate. A complete mechanism for the two individual subsequent steps is depicted in Scheme 3.30. 

Molander et al. studied the intramolecular coupling of unactivated olefinic ketones by a reductive ketyl-olefin radical cyclization, mediated by Sml2 in the presence of HMPA [47] (Scheme 18). 

C-C bond formation in inter- or intramolecular additions starting with olefin [ 199, 200], ketyl [201] (generated by PET [202], chemical or cathodic [24, 203] reduction) [204, 205] or imine radical anions [206] has become a versatile method. In general, the intramolecular addition is highly suitable for the construction of five membered rings, less so for six-, and not effective for seven-membered ring formation. 

---