Issue Date: November 4, 2013
Complex Ring Systems Made Quick And Easy
Organic chemists are always on the lookout for more efficient ways to make useful amounts of bioactive natural products or to synthesize complex molecules that can serve as pharmaceutical agents. Making molecules containing structurally diverse six-membered rings is a common feat in these preparations, but constructing five-membered carbocycle systems has lagged behind. Two research groups now report methods to quickly assemble cyclopentyl structural motifs. A team led by Daniel Romo of Texas A&M University has developed unsaturated acylammonium intermediates from readily available acid chlorides and chiral amines and demonstrated coupling them with ketomalonates to assemble lactone-fused cyclopentanes (Nat. Chem. 2013, DOI: 10.1038/nchem.1788). The process forms two rings with up to three adjacent chiral carbons (shown, top). Romo’s group has also used this chemistry to make nitrogen heterocycles (Angew. Chem. Int. Ed. 2013, DOI:10.1002/anie.201306050). And a team led by Claude Spino of the University of Sherbrooke, in Quebec, has developed chromium aminocarbene complexes tethered to dienes (bottom) that upon heating undergo an intramolecular cycloaddition reaction to make N-heterocycle-fused cyclopentenes (Org. Lett. 2013, DOI: 10.1021/ol4025887). A useful feature of the reaction is that it proceeds whether electron-deficient, electron-rich, or unactivated dienes are involved.
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