Total synthesis

About: Total synthesis is a research topic. Over the lifetime, 25578 publications have been published within this topic receiving 489319 citations.

Zr-Catalyzed Kinetic Resolution of Allylic Ethers and Mo-Catalyzed Chromene Formation in Synthesis. Enantioselective Total Synthesis of the Antihypertensive Agent (S,R,R,R)-Nebivolol

Abstract: The first enantioselective total synthesis of the antihypertensive agent (S,R,R,R)-nebivolol (3) is described. The synthesis includes the efficient (EBTHI)Zr-catalyzed kinetic resolutions of cycloheptenyl styrenyl ethers 8 and 16, which are subsequently treated with 4 mol % Mo(CHCMe2Ph)(N(2,6-(i-Pr)2C6H3))(OCMe(CF3)2)2 to afford chiral nonracemic 2-substituted chromenes (R,R)-9 and (S,R)-17. Since the present retrosynthetic analysis dissects the molecule into two chromene fragments, both the (R) and (S) antipodes of (EBTHI)Zr catalyst are required. Accordingly, Buchwald's efficient resolution process is used to resolve rac-(EBTHI)ZrCl2 (from catalytic hydrogenation of commercially available rac-(EBI)ZrCl2), such that the two requisite transition metal chiral catalysts are obtained by a single process. Other noteworthy features of the synthesis include a highly efficient, regio- and stereoselective Pd-catalyzed opening of cyclic allylic epoxide 7 with diaryloxystannane 15 and a photochemical modification o...

Total Synthesis and Immunosuppressive Activity of (−)-Pateamine A and Related Compounds: Implementation of a β-Lactam-Based Macrocyclization

Abstract: The asymmetric synthesis of the potent immunosuppressive agent (−)-pateamine A isolated from the marine sponge Mycale sp. is described. A key strategy employed in the synthesis was a β-lactam-based macrocyclization to form the 19-membered dilactone macrolide. The synthesis confirms the relative and absolute stereochemistry as 3R,5S,10S,24S and sets the stage for studies into the mechanism of action of pateamine A. Other studies and findings made in the course of the synthesis and described herein include the following: (1) a Stille coupling can be competitive with π-allyl formation, (2) SmI2 effects a mild N−O cleavage of N-benzyloxy-β-lactams, (3) the synthesis of a pateamine A-dexamethasone hybrid molecule for use in a yeast three-hybrid assay was accomplished, and (4) IC50 values were determined for synthetic and natural pateamine A and related compounds in the interleukin 2 reporter gene assay.

Pd-catalyzed enantioselective allylic substitution: new strategic options for the total synthesis of natural products.

Abstract: The enantioselective version of palladium-catalyzed allylic substitution, sometimes referred to as AAA (asymmetric allylic alkylation), has emerged as a powerful synthetic tool.[1] Since the first report of a stoichiometric AAA reaction in the 1970s,[2] it took almost 20 years of research until effective catalytic systems based on chiral ligands were developed. The major challenge in conducting such reactions enantioselectively arises from the fact that both the departure of the allylic leaving group, resulting in the formation of a cationic p-allyl–Pd complex and, in most cases, the attack of the nucleophile occur on the p face of the substrate opposite to the metal. Asymmetric induction therefore proceeds remote to the employed chiral ligands. However, some particularly successful concepts to address this issue have been devised, and over 100 catalysts have been developed.[3] Besides high levels of asymmetric induction, advantages of the AAA methodology are a broad tolerance towards functional groups and, in contrast to many other catalytic asymmetric methods, a great flexibility in the bond type to be formed. For instance, H, O, N, S, P, and C nucleophiles can be employed. Among the many new opportunities thus arising for the synthetic chemist,[4] AAA reactions of cyclic substrates of type 1 and 2 have recently proven to be of particular value as they

Total syntheses of amphidinolide X and Y.

Abstract: Concise total syntheses of the cytotoxic marine natural products amphidinolide X (1) and amphidinolide Y (2) as well as of the nonnatural analogue 19-epi-amphidinolide X (47) are described. A pivotal step of the highly convergent routes to these structurally rather unusual secondary metabolites consists of a syn-selective formation of allenol 17 by an iron-catalyzed ring opening reaction of the enantioenriched propargyl epoxide 16 (derived from a Sharpless epoxidation) with a Grignard reagent. Allenol 17 was then cyclized with the aid of Ag(I) to give dihydrofuran 19 containing the (R)-configured tetrasubstituted sp3 chiral center at C.19, which was further elaborated into tetrahydrofuran 25 representing the common heterocyclic motif of 1 and 2. The aliphatic chain of amphidinolide X featuring an anti-configured stereodiad at C.10 and C.11 was generated by a palladium-catalyzed, Et2Zn-promoted addition of the enantiopure propargyl mesylate 29 to the functionalized aldehyde 28. The preparation of the corresponding C.1-C.12 segment of amphidinolide Y relies on asymmetric hydrogenation of an alpha-ketoester, a diastereoselective boron aldol reaction, and a chelate-controlled addition of MeMgBr in combination with suitable oxidation state management for the elaboration of the tertiary acyloin motif. Importantly, the end games of both total syntheses follow similar blueprints, involving key fragment coupling processes via the "9-MeO-9-BBN" variant of the alkyl-Suzuki reaction and final Yamaguchi esterifications to forge the 16-membered macrodiolide ring of amphidinolide X and the 17-membered macrolide frame of amphidinolide Y, respectively. This methodological convergence ensures high efficiency and an excellent overall economy of steps for the entire synthesis campaign.