Stereochemical Control in the Ester Enolate Claisen Rearrangement. 2. Chairlike vs Boatlike Transition-State Selection

Article abstract of DOI:10.1021/jo00011a023

The preference for chair-and boatlike transition-state geometries in the ester enolate Claisen rearrangement of straight chain, carbocyclic, and heterocyclic propanoates was investigated.A novel stereoelectronic effect in pyranoid and furanoid glycal systems leads to a significant relative stabilisation of the boatlike vs the chairlike TS(excit.).The preferred transition state in six- and five-membered carbocyclic systems is highly dependent on steric factors, as the energy difference between chair-and boatlike TS(excit.) tends to be small.With straight-chain substrates, a significant contribution of the boatlike TS(excit.) to the rearrangement product mixture is only expected in bis-donor substituted allylic esters.