Construction of alkyl-substituted 7-norbornenones through Diels-Alder cycloaddition of electron-deficient olefins and a cyclopentadienone derivative generated in situ

Dimeric sesquiterpenoids possessing densely substituted 7-norbornenone/7-norbornenol motifs pose a considerable challenge for chemical synthesis. From a strategic perspective, one could envision intermolecular Diels-Alder cycloaddition as a straightforward method for assembling alkyl-substituted 7-norbornenones. However, this approach is hindered by lability of the required dienes, namely alkylsubstituted cyclopentadienones. Here we report a one-pot protocol for construction of alkyl-substituted7-norbornenones from electron-deficient olefins and a cyclopentenone derivative. DDQ was found to be an effective oxidant for generating a cyclopentadienone intermediate in situ from the enone. A series of sterically congested 7-norbornenone-containing polycyclic compounds were prepared by using this protocol.

Expeditious and scalable preparation of a Li-Thiele reagent for amine-based bioconjugation

Chemoselective amine bioco njugation has long been a challenge for native protein modification.Inspired by Thiele’s seminal discovery,Li and co-workers recently developed an orto-phthalaldehyde(OPA)based reagent for labeling the amino group of a protein.Here we report an expeditious and scalable synthesis of a Li-Thiele reagent featuring an arene construction strategy.The reagent contains an alkyne side chain as a handle for secondary modification.