One of My PhD Projects

Radical additions onto carbon-carbon double bonds are now well established, at least in cyclizations and polymerizations. Significant strides have been made to extend the versatility and reliability of these reactions to intermolecular systems. However, we have learned over the last few years, that more reactive radical acceptor systems are needed to make the bimolecular version truly practical.

The development of radical acceptor systems containing carbon-nitrogen double bonds has seen tremendous growth throughout the last eight years. Despite many advantages of these systems, generation of radical addition products retaining the acceptor double bond is not straightforward. We introduced triphenylgermanium hydrazones and oxime ethers as a potential solution.

Synthesis of Novel Acylgermanes

To test the radical chemistry of these novel compounds, we developed a convienient and efficient route to functionalized acylgermanes, and established chemistry to reach the desired target compounds. When we initiated this research program, existing routes involved addition of LiGePh3 to lactones or esters, giving the desired acylgermanes in 30-40% yield. The predominant side reaction was enolization of the product, thus destroying much of the lithiogermane.

Recognizing this limitation, I switched to less basic copper germanes, and added them to acid chlorides. The result: near quantitative yields of the acylgermanes. Downstream processing involved condensation with hydrazines and oxime ethers.

Publication

Full paper: U. Iserloh and D.P. Curran, Radical Cyclizations of Acylgermane Oxime Ethers and Hydrazones: Direct Routes to Cyclic Hydrazones and Oximes. J. Org. Chem. 1998, 63, 4711-16. Download PDF.