Allylic substitution rhodium catalysis

Evans and coworkers developed a rhodium-catalyzed allylic substitution of chiral acyclic tertiary allylic carbonates with acyl anion equivalents. This substitution pathway provides a route to undergo a stereo- and regioselective substitution to provide the quaternary carbon 73. The enantioenriched product is isolated in greater than 95 5 selectivity and 87% yield. This pathway provides a product that could be obtained through enolate chemistry, only lacking the same atom economy obtained with rhodium-catalysis. 

Allyl methyl ether (ethyl diazoacetate, rhodium catalysis) and allyl terf-butyl ether (dimethyl diazomalonate, copper catalysis) yield cyclopropanes exclusively. With y-substituted allyl methyl ethers, C-0 insertion is generally strongly favored over cyclopropanation, even with tetraacetatodirhodium as catalyst.In view of these findings, the cyclopropanation of ( )- ,4-dibenzyloxybut-2-ene in moderate yield, only, to give (la,2a,3j5)-31 is notable. 

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