Asymmetric Total Synthesis of Eupalinilide E, a Promoter of Human HSPC Expansion

Recent advances in the syntheses of guaianolides

Sesquiterpene lactones, especially guaianolides representing a bigger class of natural products, have served as appealing candidates for total synthesis due to their varied bio- and pharmaceutical activities. This tutorial review delineates the creative efforts of many researchers in the total syntheses of different complex guaianolides recently published in the literature. Many of the syntheses display meticulous interplay between new methods and the ingenuity of strategies achieved through well-planned routes. In some cases, the Chiron approach has come in quite handy, wherein the structural features and stereochemistry of select molecules could map well with naturally available starting materials. A few catalytic methods like diastereoselective aldol reaction, enediyne or dienyne metathesis, or photochemical methods have been efficiently used. This compilation also aims to enhance the diversity space based on these natural products and further interest in the sustainable total synthesis of this class of compounds and related molecules.

Asymmetric Synthesis of α-Methylene-γ-Butyrolactones via Tandem Allylboration/Lactonization: a Kinetic Resolution Process

The α-methylene-γ-butyrolactone motif is a widely encountered unit in many natural products and pharmaceutical compounds. Herein, a practical and efficient synthesis of α-methylene-γ-butyrolactones from readily available allylic boronates and benzaldehyde derivatives was developed with chiral N,N'-dioxide/AlIII complex as the catalyst. The key success of this transformation was the kinetic resolution of allylboration intermediate via asymmetric lactonization. This protocol enabled to assemble all of four stereoisomers from the same set of starting materials upon variable lactonization. Taking advantage of the current method as the key step, catalytic asymmetric total synthesis of eupomatilones 2, 5, and 6 was accomplished. Control experiments were carried out to probe into the tandem reaction as well as the origin of stereoselectivities.