Synthesis and Structure of 2,5-Bis[N-(2,6-mesityl)iminomethyl]pyrrolylcobalt(II): Evidence for One-Electron-Oxidized, Redox Noninnocent Ligand Behavior.

The title complex Co(Mespyr)Cl is prepared from CoCl and (Mespyr)H. Instead of the expected (Mespyr)CoCl complex, a complex with formula (Mespyr)CoCl is isolated wherein the angle strain of the Mespyr ligand results in metal ligation by only two of the three ligand donor atoms. Careful examination of structural, spectroscopic, and magnetic features indicates this compound is best described as a complex of high-spin Co(II) with a neutral radical ligand.

Asymmetric synthesis of seven-membered carbocyclic rings via a sequential oxyanionic 5-exo-dig cyclization/claisen rearrangement process. Total synthesis of (-)-frondosin B.

Appropriately substituted nonracemic allyl alcohols, readily prepared from the corresponding enones by application of the CBS methodology, were converted to optically active cycloheptenone derivatives with almost complete transfer of chirality via an efficient "one-pot", cycloisomerization/Claisen rearrangement process. This methodology was directly applied to the expedient total synthesis of (-)-frondosin B.