An acyl radical cyclization to form the bicyclic core of (-)-kumausallene (1) was the key feature in the 14-step, enantioselective synthesis. This work demonstrates that the bromoallene unit is robust enough to withstand multiple synthetic operations and provides the unambiguous assignment of the absolute configuration of the bromoallene.

Cyclic ether containing natural products represent important synthetic targets owing to their unique structural and biological properties. 1 The development of new methodology for the synthesis of this ubiquitous class of compounds has been the focus of extensive investigation for the last 20 years. However, the development of new and general methods capable of accessing this class of compounds continues to dominate this area of investigation. 2 A number of radical methods 3-5 have recently been developed for the stereoselective synthesis of cyclic ethers. Methods that utilize acyl radicals 6 have, however, not been forthcoming. In this paper, we describe the first example of the intramolecular addition of an acyl radical to a vinylogous carbonate for the efficient and stereoselective construction of 5-, 6-, and 7-membered cyclic ethers (eq 1). 7

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An acyl radical cyclization to form the bicyclic core of (-)-kumausallene (1) was the key feature in the 14-step, enantioselective synthesis. This work demonstrates that the bromoallene unit is robust enough to withstand multiple synthetic operations and provides the unambiguous assignment of the absolute configuration of the bromoallene.