Yu-Rong Yang

Iridium-Catalyzed Enantioselective Indole Cyclization: Application to the Total Synthesis and Absolute Stereochemical Assignment of (−)-Aspidophylline A

The first enantioselective total synthesis of (-)-aspidophylline A, including assignment of its absolute configuration has been accomplished. A key element of the synthesis is a highly enantioselective indole allylic alkylation/iminium cyclization cascade which was developed by employing a combination of Lewis acid activation and an iridium/ligand catalyst. This strategy relies on the direct use of 2,3-disubstituted indoles with secondary allylic alcohols appended at C2 and heteronucleophiles appended at C3, indoles which are easily prepared from simple starting materials under C-H activation conditions.

Application of the Helquist Annulation in Lycopodium Alkaloid Synthesis: Unified Total Syntheses of (-)-8-Deoxyserratinine, (+)-Fawcettimine, and (+)-Lycoflexine

A unified strategy for total synthesis of the Lycopodium alkaloids (-)-8-deoxyserratinine (7), (+)-fawcettimine (1), and (+)-lycoflexine (4) is detailed. The key features include a highly efficient Helquist annulation to assemble the cis-fused 6/5 bicycle, facile construction of the aza nine-membered ring system employing double N-alkylation strategy, providing access to the common tricyclic skeleton, asymmetric Shi epoxidation, delivering the desired β-epoxide stereospecifically to furnish (-)-8-deoxyserratinine (7), SmI(2) reduction of dihydroxylation derivative 35 to enable formation of (+)-fawcettimine (1), and a rapid biomimetic transformation of (+)-fawcettimine (1) into (+)-lycoflexine (4) via an intramolecular Mannich cyclization.

Total Synthesis of (−)-8-Deoxyserratinine via an Efficient Helquist Annulation and Double N-Alkylation Reaction

The first enantioselective total synthesis of (-)-8-deoxyserratinine has been achieved in 15 steps from enone 4 with 7% overall yield. The key features include a highly efficient Helquist annulation to furnish the cis-fused 6/5 bicycle, facile construction of the aza nine-membered ring system employing double N-alkylation strategy, as well as asymmetric Shi epoxidation, delivering the desired beta-epoxide stereospecifically.

Second Generation Synthesis of C27−C35 Building Block of E7389, a Synthetic Halichondrin Analogue

A practical method is reported to synthesize E7389 C27-C35 building block 13 from 1,2-O-isopropylidene-alpha-D-5-deoxyglucurono-6,3-lactone (3). This synthesis relies on two key processes: (1) C34/C35-diol is introduced via asymmetric dihydroxylation with dr = 3:1, with the undesired C34-diastereomer effectively removed by crystallization of 11, and (2) the C30 PhSO2CH2 group is introduced stereoselectively (>100:1) via hydrogenation of 12 in the presence of the Crabtree catalyst. The reported synthesis is practically free from chromatographic separation.

Ir-Catalyzed Asymmetric Total Synthesis of (−)-Communesin F

The first catalytic asymmetric total synthesis of the heptacyclic alkaloid (-)-communesin F is described. A key step features an iridium-catalyzed asymmetric intermolecular cascade cyclization, constructing the lower N,N-aminal-containing CDEF tetracyclic core in one step. Another notable element is the closure of final ring system (A ring) via a facile reduction of a twisted amide and concomitant cyclization activated by mesylation of N,O-hemiaminal intermediate.

Enantioselective Total Synthesis of (-)-Alstoscholarisine A

We report a concise and highly enantioselective total synthesis of (-)-alstoscholarisine A (1), a recently isolated monoterpenoid indole alkaloid that has significant bioactivity in promoting adult neuronal stem cells proliferation. A highly enantioselective (99% ee), intramolecular Ir-catalyzed Friedel-Crafts alkylation of indole 9 with a secondary allylic alcohol was utilized to establish the first stereogenic center upon which the other three contiguous chiral centers were readily set by a highly stereoselective tandem 1,4-addition and aldol reaction. The key tetrahydropyran was constructed through a hemiacetal reduction, and the final aminal bridge was forged by a one-pot reductive amination/cyclization. The conciseness of this approach was highlighted by building core bonds in each step with a minimalist protecting group strategy.

Isolation and Complete Structural Assignment of Lycopodium Alkaloid Cernupalhine A: Theoretical Prediction and Total Synthesis Validation

Cernupalhine A (1) is a trace Lycopodium alkaloid (0.7 mg) possessing a new C17N skeleton with an unusual hydroxydihydrofuranone motif newly isolated from Palhinhaea cernua L. Its complete structural assignment, including absolute stereochemistry, was established through a combination of high-field NMR techniques and computational methods and further unequivocal confirmation by the first asymmetric total synthesis. Following the first total synthesis of lobscurinine (3), 1 was achieved via regio- and stereoselective cyanide ion addition and subsequent acid treatment.

Collective Total Synthesis of Tetracyclic Diquinane Lycopodium Alkaloids (+)-Paniculatine, (-)-Magellanine, (+)-Magellaninone and Analogues Thereof

The collective total synthesis of tetracyclic diquinane Lycopodium alkaloids, (+)-paniculatine, (-)-magellanine, (+)-magellaninone, and two analogues (-)-13-epi-paniculatine and (+)-3-hydroxyl-13-dehydro-paniculatine, has been accomplished. By logic-guided addition of a strategically useful hydroxyl group at C-3 of paniculatine, the formidable tetracyclic core was rapidly synthesized utilizing a site-specific and stereoselective aldol cyclization, thus making the ABD → ABCD tetracyclic approach to diquinane Lycopodium alkaloids attainable for the first time.

Cyclization Approaching to (-)-Lycojapodine A: Synthesis of Two Unnatural Alkaloids

Two unnatural alkaloids were observed for the first time while attempting to initiate a plausibly biomimetic cyclization approaching to (-)-lycojapodine A, one of the newest Lycopodium alkaloids.

Iridium-catalyzed enantioselective allylation of silyl enol ethers derived from ketones and α,β-unsaturated ketones

The unified Ir-catalyzed enantioselective allylic substitution reactions of silyl enol ethers derived from ketones and α,β-unsaturated ketones with branched, racemic allylic alcohols are described. This transformation is catalyzed by the Carreira system and proceeds without fluoride, and with high ee and b : l ratio. The synthetic utility of this method was illustrated by the concise enantioselective total synthesis of marine natural products calyxolane A, B and by the assignment of the absolute configuration of calyxolane A.