Synthesis of Lamellarin D Trimethyl Ether and Lamellarin H via 6π-Electrocyclization.
An electrocyclic ring closure of a 2-azapentadienyl anion generated in situ from a chalcone and glycine ester is the key step of an efficient synthesis of the pyrrole core of the lamellarin alkaloids. A recently developed scalable one-pot procedure provides multigram quantities of a 3,5-diaryl-4-iodopyrrole-2-carboxylate intermediate which is transformed in four further high-yielding operations including a one-pot Pomeranz–Fritsch alkylation/cyclization and an Ullmann-type lactone ring closure into the pentacyclic lamellarin skeleton.
Diastereodivergent Synthesis of Fluorinated Cyclic β(3)-Amino Acid Derivatives.
The ability of 2-p-tolylbenzyl carbanions to behave as a source of chiral benzylic nucleophiles has been shown in its reaction with fluorinated imines. The process takes place with high levels of stereocontrol, rendering the corresponding amines as single diastereoisomers. Subsequent cross-metathesis followed by intramolecular aza-Michael reaction makes the synthesis of fluorinated homoproline derivatives bearing three stereogenic centers possible. Furthermore, the selectivity of the cyclization process can easily be tuned up in a diastereodivergent manner simply by changing the reaction conditions.