Enantioselective Robinson-type annulation reaction between β-ketoamide and α,β-unsaturated ketone was developed by utilizing the amino acid derived primary-secondary diamine catalysts. The less reactive acyclic β-ketoamides employed as both electrophile and nucleophile are reported in this asymmetric tandem reaction. A number of chiral cyclohexenone derivatives containing an amide group were obtained in high yields and good selectivities.
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Beilstein J Org Chem
December 2022
COBRA, Normandie University, 76000 Rouen, France.
A convergent approach to the skeleton of tridachiapyrone B is described taking advantage of the desymmetrization of α,α'-dimethoxy-γ-pyrone leading to α-crotyl-α'-methoxy-γ-pyrone in one step. To construct the quaternary carbon of the 2,5-cyclohexadienone of the target, a strategy based on the Robinson-type annulation of an aldehyde derived from α-crotyl-α'-methoxy-γ-pyrone was applied. The grafting of the simplified target's side chain was demonstrated through an oxidative anionic oxy-Cope rearrangement of the tertiary alcohol arising from the 1,2-addition of a 1,3-dimethylallyl reagent to 2,5-cyclohexadienone connected to the α'-methoxy-γ-pyrone motif.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
December 2020
Key Laboratory of Drug Targeting and Drug Delivery Systems of the Education Ministry and Sichuan Province, Sichuan Engineering Laboratory for Plant-Sourced Drugs and Sichuan Research Center for Drug Precision Industrial Technology, West China School of Pharmacy, Sichuan University, Chengdu, 610041, China.
The first total synthesis of liangshanone, a hexacyclic ent-kaurane diterpenoid alkaloid, has been completed. Its intricate cagelike framework was assembled through several key transformations, including an oxidative dearomatization/Diels-Alder (OD/DA) cycloaddition sequence, a tandem alkene cleavage/Mannich cyclization, a Robinson-type annulation, and an intramolecular aldol reaction. Notably, an organocatalytic enantioselective α-hydroxymethylation process allowed the preparation of an enantiomerically enriched tricyclic intermediate that should enable asymmetric access to the target natural product.
View Article and Find Full Text PDFOrg Lett
May 2019
Department of Chemistry , Indian Institute of Technology, Kanpur , Uttar Pradesh 208016 , India.
The first enantioselective total syntheses of highly complex hexacyclic meroterpenoids STR-2 and -9 (strongylophorine (STR)) are reported. Key elements of the synthetic route include the use of Robinson-type annulation reaction to construct the tricyclic terpenoid building block and a highly efficient PIDA-mediated 1,3-diaxial sp C-H activation to incorporate the requisite δ-lactone moiety. This route also enables the determination of absolute configuration of the synthesized natural products.
View Article and Find Full Text PDFChem Asian J
June 2019
Department of Synthetic Medicinal Chemistry, Faculty of Pharmaceutical Sciences, Hoshi University, 2-4-41 Ebara, Shinagawa-ku, Tokyo, 142-8501, Japan.
Highly diastereoselective total syntheses of (±)-caseabalansin A (1) and (±)-18-epicaseabalansin A (2) are described in this paper. We revealed that the intramolecular Robinson-type annulation of an alkynone was effective in the stereocontrolled construction of the bicyclic skeleton of 1 and 2. Further transformation of the resulting enone, including diastereoselective reduction by LiAlH(OtBu) , hydroxy-group-directed hydrogenation, cyclization to form the cyclic acetal moiety, and introduction of a side chain by a C(sp )-C(sp ) Stille coupling reaction, resulted in the total syntheses of (±)-1 and (±)-2.
View Article and Find Full Text PDFOrg Lett
May 2018
Department of Chemistry , Indian Institute of Technology Kanpur, Kanpur 208016 , India.
The first enantioselective total synthesis of (+)-taondiol, a pentacyclic marine meroterpenoid, has been achieved, which in addition to confirming the structure also established the absolute configuration of the natural product. The notable points in the synthetic route are synthesis of a highly functionalized tricyclic diterpenoid moiety starting from an enantiopure Wieland-Miescher ketone derivative in concise manner via Robinson-type annulation and an elegant hydrogen atom transfer olefin reduction followed by Lewis acid-catalyzed Friedel-Crafts reaction for one-pot C-C and C-O bond formations resulting in construction of the pentacyclic meroterpenoid skeleton.
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