This contribution is dedicated to the memory of Michelle M. Millar, whose talent, generosity, and thoughtfulness touched so many. ABSTRACTThe synthesis of a tunneled hollandite-type manganese oxide with interstitial and framework Cr 3+ is described. This unique material is prepared from a layered buserite precursor under conditions previously believed to only yield todorokite-type manganese oxides with larger tunnels. The influence of Cr 3+ in promoting the hollandite structure has been investigated by selectively placing the cation either in interstitial or framework sites. The use of framework Cr 3+ in combination with other interstitial cations generates related hollandite and todorokite derivatives. Catalytic oxidation reactions with benzyl alcohol and carbon monoxide have also been examined.

The tandem chain extension-aldol (TCA) reaction of β-keto esters provides a α-substituted γ-keto ester with an average syn:anti selectivity of 10:1. It is proposed that the reaction proceeds via a carbon-zinc bound organometallic intermediate potentially bearing mechanistic similarity to the Reformatsky reaction. Evidence, derived from control Reformatsky reactions and a study of the structure of the TCA intermediate utilizing DFT methods and NMR-spectroscopy, suggests the γ-keto group of the TCA intermediate plays a significant role in diastereoselectivity observed in this reaction. Such coordination effects have design implications for future zinc mediated reactions.