Investigation of Grignard Reagent as an Advanced Base for Aza-Claisen Rearrangement

Employing iPrMgCl as an advanced base instead of lithium hexamethyldisilazane (LHMDS) resulted in dramatic improvements in aza-Claisen rearrangement. This advance is considered responsible for the increased bulkiness of the alkoxide moiety (including magnesium cation and ligands), followed by a resultant conformational change of the transition state. To support this hypothesis, various substrates of aza-Claisen rearrangement were prepared and screened. In addition, a molecular dynamic simulation study was performed to investigate and compare the structural stability of reaction intermediates.

Asymmetric Synthesis of (-)-6-Desmethyl-Fluvirucinine A₁ via Conformationally-Controlled Diastereoselective Lactam-Ring Expansions

The versatile synthesis of (−)-6-desmethyl-fluvirucinine A₁ was accomplished at a 24% overall yield through a thirteen-step process from a known vinylpiperidine. The key part involved the elaboration of the distal stereocenters and a macrolactam skeleton via conformationally-induced diastereocontrol and the iterative aza-Claisen rearrangements of lactam precursors.