Enantioselective tandem formation and [2,3]‐sigmatropic rearrangement of cyclic propargylic oxonium ylides catalyzed by dirhodium(II) tetrakis[N‐phthaloyl‐(S)‐tert‐leucinate]

This paper describes the first examples of catalyst‐dependent asymmetric induction in the periselective [2,3]‐sigmatropic rearrangement of propargylic oxonium ylides generated by catalytic diazo decomposition. Catalysis of α‐diazo‐ß‐keto esters 4a—g using dirhodium(II) tetrakis[N‐phthaloyl‐(S)‐tert‐leucinate] in toluene has led to the virtually exclusive formation of benzofuran‐3‐ones bearing an allenic group with up to 79% ee.