Asymmetric Synthesis of (−)-Brevipolide H through Cyclopropanation of the α,β-Unsaturated Ketone

Copper-Mediated Decarboxylative Coupling of 3-Indoleacetic Acids with Sulfoxonium Ylides for the Synthesis of α-Acetoxyl Ketones

The most convenient and direct method of synthesizing an α-acyloxy ketone is the reaction of a diazo compound with a carboxylic acid via O-H insertion. However, due to the limitations in preparing and storing diazo compounds, the application of this method is restricted. In this study, Cu(OAc)2-mediated (OAc = acetate) decarboxylative coupling reactions of 3-indoleacetic acids with sulfoxonium ylides were developed for use in rapidly synthesizing α-acetoxyl ketones. In this reaction, Cu(OAc)2 was not only used as an oxidant, but also as acetate ion source. Notably, when 5-methoxy-2-methyl-3-indoleacetic acid reacted with different sulfoxonium ylides, the corresponding products exhibited fluorescence, and furthermore, several products displayed antiproliferative activities against various human cancer cell lines.

Asymmetric transformations from sulfoxonium ylides

Sulfoxonium ylides are important surrogates for diazo compounds, and their use in industry as safer alternatives has been evaluated during recent years. Beyond the known classical transformations, these ylides have also been used in a surprising plethora of novel and intrinsic chemical reactions, especially in recent years. Bench stability and handling are also an advantage of this class of organosulfur molecules. Despite this, efficient asymmetric transformations, specifically catalytic enantioselective versions, have only recently been reported, and there are specific reasons for this. This perspective article covers this topic from the first studies up to the latest advances, giving personal perspectives and showing the main challenges in this area in the coming years.

Chiron approach for the total synthesis of brevipolide M

An efficient stereoselective synthesis of brevipolide M was established in 13 linear steps and 17.8% overall yields base on chiron approach. The key steps of our synthesis involved tandem homologation / tetrahydrofuran cyclization and sequential ring-closing metathesis (RCM) / double-bond migration in one-pot processes.

Stereoselective Total Synthesis of (+)-Brevipolide H from d-Galactal

An efficient and concise synthesis of cytotoxic 5,6-dihydro-α-pyrone (+)-brevipolide H has been accomplished in 12 long linear steps in 8.65% overall yield from readily available chiral synthons, d-galactal and ethyl l-lactate. The features of this synthesis are highly diastereoselective Simmons–Smith cyclopropanation and carbohydrate-based chiron approach to rapid access to key 5,6-dihydro-α-pyrone skeleton.

Strategies for the synthesis of brevipolides

In recent years fifteen 5,6-dihydro-α-pyrone derivatives, bearing either a distinctive cyclopropane or furan ring and named brevipolides A–O (1–15), have been isolated from the invasive plant Hyptis brevipes Poit. Their fascinating structural features, and the potent biological activities, including cytotoxicity against an array of human cancer cell lines and inhibition of the chemokine receptor CCR5, make them attractive synthetic targets. This review article highlights the recent synthetic methodologies and briefly summarizes their biological activities.

First stereoselective total synthesis of brevipolide M

The first stereoselective total synthesis of a cytotoxic brevipolide M, which shares a pyrone framework bearing a tetrahydrofuran moiety and a cinnamate group with the readily available (-)-DET, is described. The key steps involved in the synthesis are the epoxide-opening, Brown's allylation, and the RCM reaction to install an α,β-unsaturated lactone ring and the inversion of the C-6' stereogenic hydroxyl group using the Mitsunobu reaction.

Enantioselective synthesis of (+)-brevipolide H

The enantioselective synthesis of natural brevipolide H is reported for the first time. By way of Sharpless epoxidation of penta-1,4-dien-3-ol, both enantiomerically pure epoxides were converted to the corresponding olefins for cross metathesis. Subsequent transformations, including epoxide ring opening, esterifications, cyclopropanation, oxidation and ring-closing metathesis, provided the target molecule. This synthesis successfully addresses previous shortcomings in preparing brevipolides.

Anti-addition of Dimethylsulfoxonium Methylide to Acyclic α,β-Unsaturated Ketones and Its Application in Formal Synthesis of an Eicosanoid

Cyclopropanation using dimethylsulfoxonium methylide (Corey-Chaykovsky reaction) was examined with a series of linear α,β-unsaturated ketones, and the results showed that the major trajectory for the addition of the sulfur ylide to the enones is anti, related to the γ-substituent. The stereochemical assignment for the generated cyclopropanes was achieved by X-ray crystallography or comparing with the reported spectroscopic data. We found that the diastereoselectivity was influenced by several factors, including the protecting groups, solvents, and temperatures, and good anti/syn ratios (>10:1) were often obtained using the tert-butyldimethylsilyl and tert-butyldiphenylsilyl-protected substrates. The method was applied to a formal synthesis of a natural eicosanoid with good efficiency.