Intramolecular cyclopropene-furan [2 + 4] cycloaddition followed by a cyclopropylcarbinyl rearrangement to synthesize the BCD rings of cortistatin A.

A concise bioinspired synthesis of Schisandra nortriterpenoid propindilactone G has been accomplished from a readily accessible steroidal lactone. Key transformations include a Breslow remote functionalization, a Suarez remote radical functionalization, a ring expansion enabled by a Wagner-Meerwein rearrangement, a stereoinversion of a tertiary alcohol, and a biomimetic transesterification/oxa-Michael addition cascade. This work also provides experimental evidence of the putative propindilactone G biosynthesis pathway.

Bioinspired Synthesis of Nortriterpenoid Propindilactone G.

Limonoid and limonoid-like natural products have demonstrated diverse bioactive properties and attracted considerable synthetic efforts. They provide a good platform to examine the viability of methodologies in the efficient construction of complex skeletons. In this review, we have discussed the recent progress in the syntheses of limonoids and limonoid-like natural products, covering from January 2011 to March 2020. The key transformations are highlighted. Finally, we summarize current “state-of-art” advance on novel synthetic strategy in syntheses of linonoids and limonoid-like molecules. Besides, future outlook are also presented.

Recent progress in the synthesis of limonoids and limonoid-like natural products

Cyclization of squalene-2,3-epoxide to 10α-cucurbita-5,24-dien-3β-ol by microsomes from Cucurbita maxima seedlings

A remarkable characteristic of naturally occurring terpenes is the bewildering array of carbocyclic structures. As of 1970 more than 200 different carbon skeletons had been identified (excluding nor metabolites), the structures varying from acyclic chains to hexacyclic ring systems and containing almost all ring sizes from three to fourteen members (1). Although a considerable number of the 200 are produced by oxidative transformations (e. g., ring cleavage) of pre-existing terpenes, a majority nevertheless represent primary structures formed in nature through multistep cyclization and rearrangement sequences originating from five basic acyclic precursors.

Biogenetic-type rearrangements of terpenes.

3β-Acetoxy- and 3β-benzoyloxy-lanost-24-en-11β-ol nitrites, readily available from lanosterol, on photolyis in the presence of iodine give 19-iodo-derivatives. By further transformations cycloartenol has been obtained. The formal total synthesis of this latter compound is, therefore, complete. Photolysis of the above mentioned nitrites in the absence of iodine gives the corresponding 19-oximino- and thence 19-cyano-derivatives. Such derivatives have not, so far, been converted into cycloartenol.

L. J. Danks

Papers

Photochemical transformations. Part XXV. The synthesis of cycloartenol

The synthesis of cycloartenol