Facile construction of the pentacyclic framework of subincanadine B. Synthesis of 20-deethylenylated subincanadine B and 19,20-dihydrosubincanadine B.

[reaction: see text] We describe a facile approach for effectively constructing the pentacyclic framework of subincanadine B. The seven-step assembly of tetracyclic ketone 14 featured Michael addition, Pictet-Spengler cyclization, and Dieckmann condensation. From this key ketone intermediate, two analogues of subincanadine B, i.e., 20-deethylenylated subincanadine B (27) and 19,20-dihydrosubincanadine B (31), were synthesized in four steps, respectively.

One-step assembly of functionalized gamma-butyrolactones from benzoins or benzaldehydes via an N-heterocyclic carbene-mediated tandem reaction.

We describe here a direct, efficient, one-step construction of gamma,gamma-difunctionalized gamma-butyrolactones from benzoins or benzaldehydes via a tandem reaction promoted by 1,3-dimethyl imidazolin-2-ylidene, an N-heterocyclic carbene (NHC). [reaction: see text]