Rapid synthesis of bicyclic lactones via palladium-catalyzed aminocarbonylative lactonizations

Convergent and Efficient Total Synthesis of (+)-Heilonine Enabled by C-H Functionalizations

We report a convergent and efficient total synthesis of the C-nor D-homo steroidal alkaloid (+)-heilonine with a hexacyclic ring system, nine stereocenters, and a trans-hydrindane moiety. Our synthesis features four selective C-H functionalizations to form key C-C bonds and stereocenters, a Stille carbonylative cross-coupling to connect the AB ring system with the DEF ring system, and a Nazarov cyclization to construct the five-membered C ring. These enabling transformations significantly reduced functional group manipulations and delivered (+)-heilonine in 11 or 13 longest linear sequence (LLS) steps.

Synthesis and medicinal chemistry of tetronamides: Promising agrochemicals and antitumoral compounds

Butenolides and tetronic acids occupy a prominent position in synthetic chemistry due to their ubiquitous distribution in nature. This has stimulated investigations firstly in the synthesis of such systems and, laterly, the interest has turned to the understanding of the quantum structure of such systems, allowing a deeper understanding of the mechanism and reactivity of this cyclic scaffold. In contrast, tetronamides, which consist of compounds bearing a 4-aminofuran-2(5H)-one backbone, are relatively rare in nature and synthetic routes to such compounds are poorly explored. This review highlights both the importance of the tetronamide scaffold in medicinal chemistry and the most relevant recondite synthetic strategies for obtaining compounds of this class.

Enantioselective Total Syntheses of the Proposed and Revised Structures of Methoxystemofoline: A Stereochemical Revision

This article describes the full details of our synthetic efforts toward the enantioselective total synthesis of the complex alkaloid methoxystemofoline. The enantioselective construction of the tetracyclic core features: (1) the Keck allylation at the N-α bridgehead carbon to forge the tetrasubstituted stereocenter; (2) an olefin cross-metathesis reaction for the side-chain elongation that is amenable for the synthesis of congeners and analogues; and (3) a regioselective aldol addition reaction with methyl pyruvate that ensured the subsequent regioselective cyclization reaction to construct the fourth ring. Overman's method was employed to install the 5-(alkoxyalky1idene)-3-methyl-tetronate moiety. In the last step, a nonstereoselective reaction resulted in the formation of both the proposed structure of methoxystemofoline and its E-stereoisomer, the natural product (revised structure), in a 1:1 ratio. We suggest to rename the natural product as isomethoxystemofoline, and report for the first time the complete ¹H NMR data for this natural product.

Synthesis of 1,6-Dihydropyridine-3-carbonitrile Derivatives via Lewis Acid-Catalyzed Annulation of Propargylic Alcohols with (E)-3-Amino-3-phenylacrylonitriles

A novel Lewis acid-catalyzed, highly efficient, practical, and atom-economical protocol for the synthesis of functionalized 1,2-dihydropyridine-3-carbonitrile derivatives in the presence of Bi(OTf)₃ (10 mol %) in tetrahydrofuran (2.0 mL) at 80 °C for 8 h in air is described, starting from readily accessed propargylic alcohols and (E)-3-amino-3-phenylacrylonitriles. This cycloaddition protocol, which is scalable and proceeds under mild conditions, is amenable to the gram-scale construction of valuable 1,2-dihydropyridine-3-carbonitriles. Furthermore, the good functional group compatibility and broad scope of this strategy were demonstrated by a broad range of propargylic alcohols and (E)-3-amino-3-phenylacrylonitriles, with yields ranging from 34 to 96%.

A transition metal-free approach towards the regioselective synthesis of β-carboline tethered pyrroles and 2,3-dihydro-1H-pyrroles

A transition metal-free one-pot sequential approach has been unfolded for the synthesis of β-carboline tethered pyrroles and 2,3-dihydro-1H-pyrroles by using highly diverse 1-formyl-9H-β-carbolines as a template.

Total Synthesis, Biological Evaluation, and Target Identification of Rare Abies Sesquiterpenoids

Abiespiroside A (1), beshanzuenone C (2), and beshanzuenone D (3) belong to the Abies sesquiterpenoid family. Beshanzuenones C (2) and D (3) are isolated from the critically endangered Chinese fir tree species Abies beshanzuensis and demonstrated weak inhibiting activity against protein tyrosine phosphatase 1B (PTP1B). We describe herein the first total syntheses of these Abies sesquiterpenoids relying on the sustainable and inexpensive chiral pool molecule (+)-carvone. The syntheses feature a palladium-catalyzed hydrocarbonylative lactonization to install the 6,6-fused bicyclic ring system and a Dreiding-Schmidt reaction to build the oxaspirolactone moiety of these target molecules. Our chemical total syntheses of these Abies sesquiterpenoids have enabled (i) the validation of beshanzuenone C's weak PTP1B inhibiting potency, (ii) identification of new synthetic analogs with promising and selective protein tyrosine phosphatase SHP2 inhibiting potency, and (iii) preparation of azide-tagged probe molecules for target identification via a chemoproteomic approach. The latter has resulted in the identification and evaluation of DNA polymerase epsilon subunit 3 (POLE3) as one of the novel cellular targets of these Abies sesquiterpenoids and their analogs. More importantly, via POLE3 inactivation by probe molecule 29 and knockdown experiment, we further demonstrated that targeting POLE3 with small molecules may be a novel strategy for chemosensitization to DNA damaging drugs such as etoposide in cancer.

Total Syntheses of Bisdehydroneostemoninine and Bisdehydrostemoninine by Catalytic Carbonylative Spirolactonization

The first total syntheses of the stemona alkaloids bisdehydroneostemoninine and bisdehydrostemoninine in racemic forms have been achieved. The synthetic strategy features a novel palladium-catalyzed carbonylative spirolactonization of a hydroxycyclopropanol to rapidly construct the oxaspirolactone moiety. It also features a Lewis acid promoted tandem Friedel-Crafts cyclization and lactonization to form the 5-7-5 tricyclic core of the target stemona alkaloids.

One-Pot Multicomponent Mechanosynthesis of Polysubstituted trans-2,3-Dihydropyrroles and Pyrroles from Amines, Alkyne Esters, and Chalcones

An efficient and practical one-pot multicomponent reaction of amines with alkyne esters and chalcones promoted by I₂/PhI(OAc)₂ has been developed under solvent-free ball-milling conditions to afford a variety of polysubstituted trans-2,3-dihydropyrroles in moderate to good yields. The present method features a short reaction time, mild reaction conditions, broad substrate scope, and feasibility of large-scale synthesis. Intriguingly, this protocol can also furnish the corresponding synthetically more attractive pyrroles with the addition of an oxidant in a one-pot way.

2,3-Allenoic acids via palladium-catalyzed carboxylation of propargylic alcohols

The first example of Pd-catalyzed carboxylation of propargylic alcohols in the presence of CO (1 atm) and water affording 2,3-allenoic acids has been developed.