Non-Carbonyl-Stabilized Metallocarbenoids in Synthesis: The Development of a Tandem Rhodium-Catalyzed Bamford−Stevens/Thermal Aliphatic Claisen Rearrangement Sequence

摘要

A tandem rhodium-catalyzed Bamford−Stevens/Claisen rearrangement is presented. The tandem reaction uses Eschenmoser hydrazones for the in situ generation of non-carbonyl-stabilized diazo alkanes, which are presumably intercepted by Rh(II) catalysts to induce a 1,2-hydride migration. This sequence provides high levels of stereocontrol for the generation of simple acyclic (Z)-enol ethers. These enol ethers undergo either thermal or Lewis acid accelerated Claisen rearrangements to provide products of high diastereopurity. Also presented are cascade reactions, wherein a third chemical step occurs after the initial tandem sequence (i.e., Bamford−Stevens/Claisen/ene and Bamford−Stevens/Claisen/Cope).