Asymmetric Synthesis of Cyclopentene Compounds Containing All-Carbon Quaternary Stereocenters by (3 + 2) Cycloaddition and Its Application in the Formal Synthesis of (R)-(−)-Puraquinonic Acid

Abstract

A highly stereoselective (3 + 2) cycloaddition for the asymmetric synthesis of versatile cyclopentene compounds containing all-carbon quaternary stereocenters was developed. The phosphine-catalyzed reactions of alkynoates with α-alkylated electron-deficient alkenes bearing Oppolzer’s camphorsultam showed high to excellent diastereoselectivities and perfect regioselectivities. The usefulness of this reaction was demonstrated in the concise formal synthesis of (R)-(−)-puraquinonic acid.

Total Synthesis of the Diterpenes (+)-Randainin D and (+)-Barekoxide via Photoredox-Catalyzed Deoxygenative Allylation

“…Despite the significant development in the field of RCM, its application to the synthesis of tetrasubstituted olefins remains a significant challenge . In fact, to the best of our knowledge, RCM has never been employed in total synthesis to generate a tetrasubstituted cycloheptenone. , To our delight, when 7 was treated with 10 mol % of Hoveyda–Grubbs second-generation catalyst (HG-II) in toluene at 110 °C, the desired trans -hydroazulenone 6 was obtained in 36% yield, along with 48% of the recovered starting material. Several commercially available RCM catalysts, including the molybdenum-based Shrock catalyst, were evaluated, showing that the HG-II was the most efficient (see Supporting Information).…”

Sodiated Oppolzer enolates: solution structures, mechanism of alkylation, and origin of stereoselectivity

“…4 Curiously, several recent reactions that do not involve potentially chelate-forming at all can be explained by the same stereoelectronic control. 24 One might surmise that the only advantage of sodium over lithium is the much higher reactivity but that would be wrong. The lithium and sodium enolates studied show a threefold greater reactivity of the lithium enolate.…”

Recent Progress on the [3+2] Cycloaddition Route for the Synthesis of All-Carbon Quaternary Stereocentres

“…47 Very recently Takao and co-workers have also utilized this strategy for synthesis of cyclopentene molecules possessing all-carbon quaternary stereocentres using Oppolzer's camphor sultam 113 as one of the reaction partners. 48 The camphor sultam acts as a chiral auxiliary in this reaction which is subsequently removed by chemoselective hydrolysis using alkaline hydrogen peroxide to furnish carboxylic acid 115 in 94% yield (Scheme 27). The high regioselectivity is probably due to the bulkiness of the camphor sultam.…”