Pinacol Coupling Strategy for the Construction of the Bicyclo[6.4.1]tridecane Framework of Schiglautone A

Stereoselective Synthesis of the Core Ring System of Lancifonins A-D

A 5/5/7 tricyclic intermediate bearing an oxa-bridged hemiketal ring was successfully synthesized from dihydrocarvone in 14 steps, which is a common intermediate of various Schisandra nortriterpenoids. Subsequently, the core structure of lancifonins A-D, characterized by a 5/5/7/8 fused ring system, was constructed in seven steps. The route employs key transformations, including the aldol reaction, Mukaiyama hydration, Mn(III)-mediated cyclization, the Suzuki reaction, and McMurry coupling.

Synthesis of the ABC ring system of kadlongilactones

A racemic approach towards the synthesis of the ABC (7/7/5) ring system of Schisandra triterpenoid kadlongilactones is described. The synthesis features two key transformations: (1) conjugate addition followed by iodolactonization to build the cis-fused 7/7 ring; and (2) conjugate addition-Rubottom oxidation cascade followed by ring-closing metathesis to construct the 7/7/5 tricyclic ring.

Electrochemical formal homocoupling of sec-alcohols

Electrochemical pinacol coupling of carbonyl compounds in an undivided cell with a sacrificial anode would be a promising approach toward synthetically valuable vic-1,2-diol scaffolds without using low-valent metal reductants. However, sacrificial anodes produce an equimolar amount of metal waste, which may be a major issue in terms of sustainable chemistry. Herein, we report a sacrificial anode-free electrochemical protocol for the synthesis of pinacol-type vic-1,2-diols from sec-alcohols, namely benzyl alcohol derivatives and ethyl lactate. The corresponding vic-1,2-diols are obtained in moderate to good yields, and good to high levels of stereoselectivity are observed for sec-benzyl alcohol derivatives. The present transformations smoothly proceed in a simple undivided cell under constant current conditions without the use of external chemical oxidants/reductants, and transition-metal catalysts.

Total Synthesis of Kadcoccinic Acid A Trimethyl Ester

The first total synthesis of the trimethyl ester of kadcoccinic acid A is described. The central structural element of our synthesis is a cyclopentenone motif that allows the assembly of the natural product skeleton. A gold(I)-catalyzed cyclization of an enynyl acetate led to efficient construction of the cyclopentenone scaffold. In this step, optimization studies revealed that the stereochemistry of the enynyl acetate dictates regioisomeric cyclopentenone formation. The synthesis further highlights an efficient copper-mediated conjugate addition, merged with a gold(I)-catalyzed Conia-ene reaction to connect the two fragments, thereby forging the D-ring of the natural product. The synthetic strategy reported herein can provide a general platform to access the skeleton of other members of this family of natural products.

Aspects in the Total Syntheses of Higher Terpenoids Starting From Wieland–Miescher Ketone and Its Derivative: A Review

Synthetic studies of higher terpenoids starting from Wieland–Miescher ketone since 2012 have been compiled.

Unexpected Racemization in the Course of the Acetalization of (+)-(S)-5-Methyl-Wieland–Miescher Ketone with 1,2-Ethanediol and TsOH under Classical Experimental Conditions

(+)-(S) and (−)-(R)-5-methyl-Wieland-Miescher ketone (+)-1 and (−)-1, are important synthons in the diastereo and enantioselective syntheses of biological and/or pharmacological interesting compounds. A key step in these syntheses is the chemoselective C(1)O acetalization to (+)-5 and (−)-5, respectively. Various procedures for this transformation have been described in the literature. Among them, the classical procedure based on the use of 1,2-ethanediol and TsOH in refluxing benzene in the presence of a Dean-Stark apparatus. Within our work on bioactive natural products, it occurred to us to observe the partial racemization of (+)-5 in the course of the acetalization of (+)-1 by means of the latter methodology. Aiming to investigate this drawback, which, to our best knowledge, has no precedents in the literature, we acetalized with 1,2-ethanediol and TsOH in refluxing benzene and in the presence of a Dean–Stark apparatus under various experimental conditions, enantiomerically pure (+)-1. It was found that the extent of racemization depends on the TsOH/(+)-1 and 1,2-ethanediol/(+)-1 ratios. Mechanism hypotheses for this partial and unexpected racemization are provided.

Strategy towards the enantioselective synthesis of schiglautone A

The enantioselective synthesis of a functionalized intermediate comprising 6 of the 7 stereocenters of schiglautone A is reported and features a lithiation–borylation enzymatic resolution sequence.