Enones Barbier reaction

Exceptionally clean cyclization can be accomplished by utilizing conjugated enones as precursors for the Barbier reaction (equation 43). High diastereoselectivity is achieved in these reactions, and under the mild conditions required for cyclization the TMS ether protecting group remains intact. It is also interesting that a neopentyl halide is effective in the cyclization. This result would appear to exclude an 5N2-type displacement of an organic halide by a samarium ketyl as a possible mechanism for the Smh-promoted intramolecular Barbier reaction. 

Barbier reactions. Allylation of aromatic aldehydes in 0.1 N ammonium chloride solution using a combination of Mg and an allyl bromide or iodide (but not ally chloride) has been demonstrated." Unfortunately, aliphatic aldehydes give complex mixtures. However, conjugate addition to enones can be achieved with mediation by Cul. 

Barbier/aldol reactions of enones. The iodo enone 1 on treatment with Sml2 (2 equiv.) in THF containing DMPU (10 cquiv.) undergoes reductive cyclization to the bicyclo[3.3.0]octane-3-one (2) in 70% yield. Such reductive cyclizations have been effected with a tin hydride. The advantage of the Sml2 reaction is that it proceeds... 

---