The enantioselective allenoate Claisen rearrangement is a type of [3,3] sigmatropic rearrangement that converts the pi bonds of an allene to a favorable, carbonyl group. Previous researchers have demonstrated that this reaction likely proceeds via a Zimmerman-Traxler chair-like transition state, resulting in the highly diastereoselective formation of the reaction products. However, the development of an asymmetric variant of this reaction has proven elusive.<br/><br/>Recent work in our laboratory has shown that the allenoate Claisen reaction can be made asymmetric via the use of a chiral amine as an auxiliary, which can be removed via hydrolysis upon reaction completion using hydrochloric acid. After a series of solvent and catalyst screens, it was determined that the best results were achieved using 10 mol% of silicated-tosic acid as the reaction catalyst in a 1:1 mixture of nitromethane/dichloromethane as the reaction solvent, affording up to &gt;98% yield and 96% ee of the desired allenoate Claisen product after 24 hours.<br/><br/>This reaction methodology has several attractive features: the chiral amine can be recovered via a simple extraction, and the catalyst readily removed via filtration. This reaction represents the first example of an enantioselective and diastereoselective allenoate Claisen reaction. Results reported herein have focused on expanding the substrate scope of this reaction, particularly with substrates resulting in the diastereoselective preparation of chiral reaction products.

Development of an enantioselective allenoate Claisen rearrangement

2019 Spring National Meeting

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